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FNH 302 > Midterm Material > Flashcards

Midterm Material Flashcards

1
Q

Why analyse food? [4]

A
  1. Food safety
  2. Government regulations: [4]
    1. Nutrition labelling
    2. Standards - mandatory and voluntary
    3. Food inspection and grading
    4. Authenticity
  3. Quality control (QC, QA, QM)
  4. Research and development
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2
Q

Explain what an ‘Official Method of Analysis’ for a given analyte/food is, and where you could find one.

A

Official methods of analysis = carefully developed methods, standardized & tested by collaborative study by several labs

Official or approved methods published by various nonprofit scientific organizations, e.g.,:

  • AOAC International
  • AACC
  • AOCS
  • American Public Health Association
  • Codex Alimentarius Commission
  • US Pharmacopeia (Food Chemicals Codex)
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3
Q

Describe and contrast accuracy and precision.

A

Precision → measure of repeatability; how close are replicate measurements? → assess by standard deviation and coefficient of variation

Accuracy → how close a measurement is to the true value; comparison of mean to true value → assess by absolute error or relative error

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4
Q

Describe the three main types of error.

A

Systematic error → results consistently deviate from the true value

Random error → fluctuate around the true value and are unavoidable (but try to minimize!)

Blunders → human error (i.e., big ‘screwup’)

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5
Q

Define sensitivity.

A

Magnitude of change in measurement with change in concentration of compound

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6
Q

Define selectivity.

A

Measuring only what you’re interested in measuring

e.g., total sugar content

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7
Q

Define Limit of Detection (LOD) and Limit of Quantification (LOQ).

A

Lowest amount to detect or quantify with statistical significance

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8
Q

Evaluate the quality of linear regression of a standard curve.

A

R2 value

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9
Q

Explain the basic concept of a control chart (what it is and its use).

A

Control charts monitor specific methods/processes (e.g., moisture content data after drying process).

Create control charts by gathering and plotting data over time, and using SD to determine acceptable limits (e.g., upper & lower limits = mean +/- 3*SD)

Use control charts and limits to determine if there is variation outside normal range.

If there is variation, cause must be determined so corrective and preventive actions can be enacted.

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10
Q

Describe several ways to limit undesirable changes to samples. [8]

A
  • Cryogrinding
  • Enzyme inactivation
  • Low temperature
  • Add preservatives
  • Drying
  • Add antioxidants
  • Limit light
  • Limit oxygen exposure
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11
Q

Explain what ‘proximate analysis of food’ is.

A
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12
Q

Explain the difference between Direct and Indirect methods of moisture analysis.

A
  • Direct methods → based on removal of water
    • removal of moisture (drying, distillation, extraction)
    • measure water removed by mass, volume, titration
    • oven-drying, distillation, Karl Fischer titration
  • Indirect methods → based on measurement of physical properties related to water content
    • Capacitance, specific gravity, density, refractive index, freezing point, EM absorption
    • Hydrometer, pycnometer, refractometer, IR and MW absorbance
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13
Q

Describe oven drying methods of moisture analysis, mentioning (1) principle of method, (2) inherent assumptions made, (3) sources of error [8], (4) applicability to certain types of foods, and (5) use as a QC method &/or official method.

A
  • (1) Sample is heated to evaporate off water
  • (2) Mass loss equals moisture content and all water has been driven off during drying.
  • (3) Particle size, volatile compounds, lipid oxidation, hygroscopicity, carbohydrate alteration, surface crust, splattering, improper storage
  • (4) Forced draft ovens can run many samples at once, Vacuum ovens reduce issues with decomposition, Microwave, Infrared drying, and rapid moisture analyzers for QC methods.
  • (5) Both.
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14
Q

Calculate % moisture content and % total solids.

A

Via oven drying method

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15
Q

Explain why knowing the moisture content of food is important.

A

The analysis of moisture content is essential to the food industry to control for the quality of the food, as well as the shelf life, in addition to helping food manufacture companies adhere to legal and labeling requirements.

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16
Q

Define ash in proximate analysis of food and describe its importance.

A
  • inorganic residue remaining after either incineration or complete oxidation of organic matter in a foodstuff
    • Total ash
    • also, water-soluble/insoluble, acid-insoluble
  • IMPORTANCE
    • part of proximal analysis for nutritional evaluation
    • first step in preparing sample for analysis of specific elements
    • crude measure of extent of refinement
      • Flour, sugar, rice
    • quality factor for some foods/ingredients
      • specifications for flours, grains,
      • transition metals in lipid-rich foods can speed rancidity
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17
Q

Compare dry ashing versus wet ashing.

A
  • Dry ashing → primarily used to determine % ash
    • time consuming (overnight)
    • many samples at a time
    • very high temperatures
    • sensitive to sample composition
    • less supervision required
    • no/small reagent blank
    • muffle furnace
  • Wet ashing → primarily used as sample preparation for specific mineral analysis of individual minerals
    • faster (unless using a microwave to perform the dry ashing, then dry ashing can be faster)
    • fewer samples at a time
    • moderate temperatures
    • less sensitive to sample composition
    • more hazardous
    • reagent blank required
    • fume hood, hot plate
  • Microwave ashing → can be wet or dry
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18
Q

Describe several factors that influence the accuracy & precision of ash analysis.

A
  • Ash content is relatively low
    • Pay special attention to sample preparation
    • Crucial to avoid contamination by inorganics during handling and preparation e.g., grinders, crucibles, glassware
      • Run a blank sample; rinse with HCl
  • Temperature for (dry) ashing is very high
    • samples high in fat, sugar or moisture may need additional steps before ashing
    • minimization or avoidance of splattering e.g., pre-drying, fat extraction
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19
Q

Calculate % ash on both a dry basis and a wet basis.

A
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20
Q

What is analysed?

A

Food Analysis includes: [4]

  • Chemical analysis and characterization of food components
  • Physical analysis of food
  • Microbiological analysis
  • Sensory analysis
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21
Q

When do we sample and analyse?

A

Ingredients (raw materials): specifications; certificate of analysis

→

Processing: process control

→

Final Product: consistent quality; acceptable; nutrition labelling; legal requirement; nutrient content claim, health claim

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22
Q

Who does food analysis? [4]

A
  • Government labs
    • CFIA
    • Health Canada
    • BC Centre for Disease Control (BCCDC)
  • Commercial Analytical labs (e.g., in GV):
    • Bureau Veritas Canada (formerly Maxxam Analytics)
    • SGS Labs
    • Mériuex NutriSciences (formerly Silliker JK Labs)
  • Academic, non-profit
  • In-house company labs
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23
Q

Where does food analysis happen?

A
  • In laboratories (analysis that requires preparation)
  • In the field (hand-held/portable devices)
  • On-line (i.e., directly on the processing line, not on the internet)
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24
Q

Describe considerations about the nature of the product that may affect the choice of sampling plans.

A
  • Homogenous → uniform throughout and identical in all locations
  • Heterogenous → where a sample is taken will affect data
  • Discrete → compartmentalized
  • Continuous → different parts of the sample are not physically separated
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25
Q

Describe the purpose of grinding in sample preparation, and considerations regarding the sample characteristics and sources of error.

A
  • Results in size reduction & homogenization
  • Moist samples → bowl cutters, meat mincers, blenders
  • Dry samples → mortars and pestles, mills
  • Grinding can cause (1) moisture loss, (2) chemical changes, and (3) metal contamination.
  • Reduce undesirable changes by grinding frozen samples.
  • Determine and control particle size through sieving or dynamic light scattering for particles <50um
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26
Q

Describe enzyme inactivation in sample preparation.

A
  • Denature/unfold by:
    • Heating
    • Changing pH
    • (high pressure)
  • Inactivate by:
    • Changing pH
    • Adding salt
    • Adding reducing agents
    • Adding inhibitors
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27
Q

Describe how lipid oxidation may be prevented in sample preparation.

A
  • Remove reactants, slow the reaction
  • Limit oxygen exposure (store under nitrogen, or in a vacuum)
  • Lower temperature
  • Limit light
  • Add antioxidants
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28
Q

Describe prevention of microbial growth in sample preparation.

A
  • Low temperature
  • Drying
  • Freeze-drying
  • Add preservatives
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29
Q

List four major considerations when choosing a method of analysis.

A
  • Objective of the analysis → e.g., quality control/monitoring, nutritional labelling, health claim, detecting food fraud
  • Properties of the sample → consideration of food composition and characteristics → e.g., major chemical components, liquid or solid/dry powder, stable or reactive, amount available, preparation required
  • Characteristics of the method
    • Inherent properties → specificity; precision; accuracy; sensitivity
    • Applicability of method to laboratory → sample size, reagents, equipment, cost
    • Usefulness → time required, reliability, need
    • Personnel → safety, training, competent
  • Validity of the method → representative sample and number of samples; proper calibration; use of standard reference materials or check samples; adequate procedure; repeatable results
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30
Q

Determine the number of significant figures in a value.

A

To determine the number of significant figures in a number use the following 3 rules:

  1. Non-zero digits are always significant
  2. Any zeros between two significant digits are significant
  3. A final zero or trailing zeros in the decimal portion ONLY are significant

Example:

.500 or .632000 the zeros are significant

.006 or .000968 the zeros are NOT significant

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31
Q

What are the addition and subtraction rules for significant figures?

A

For addition and subtraction use the following rules:

  1. Count the number of significant figures in the decimal portion ONLY of each number in the problem
  2. Add or subtract in the normal fashion
  3. Your final answer may have no more significant figures to the right of the decimal than the LEAST number of significant figures in any number in the problem.
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32
Q

What are the multiplication and division significant figure rules?

A

For multiplication and division use the following rule:

  1. The LEAST number of significant figures in any number of the problem determines the number of significant figures in the answer. (You are now looking at the entire number, not just the decimal portion)

*This means you have to be able to recognize significant figures in order to use this rule*

Example: 5.26 has 3 significant figures

6.1 has 2 significant figures

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33
Q

Describe distillation methods of moisture analysis, mentioning (1) principle of method (2) inherent assumptions made (3) sources of error (4) applicability to certain types of foods (5) use as a QC method &/or official method.

A
  • (1) sample is heated in an immiscible liquid like toluene and co-distilled, distillate is collected and volume of water removed is measured.
  • (2)
  • (3) clinging water droplets; water-solvent emulsions
  • (4) spices, cheese, animal feed, nuts, oils; not amenable to routine testing of many samples; less thermal degradation than oven drying
  • (5) AOAC method for spices
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34
Q

Describe chemical titration methods of moisture analysis, mentioning (1) principle of method (2) inherent assumptions made (3) sources of error (4) applicability to certain types of foods (5) use as a QC method &/or official method.

A
  • (1) K-F titration is based on a stoichiometric reaction involving reduction of iodine by sulfur dioxide in the presence of water; titration of sample with K-F reagent (contains I2); reach endpoint of titration when excess I2 has no water to react with (visually = red/brown, or based on conductance); volume of titrant is used to determine % moisture.
  • (2)
  • (3) atmospheric moisture, moisture adhering to apparatus, interferences (e.g., ascorbic acid, carbonyl compounds, unsaturated fatty acids)
  • (4) low-moisture foods, especially those high in sugar, protein, or unstable to heat or vacuum e.g., dried fruits & veg, candy, chocolates, coffee, oils & fats; may need pre-extraction of water (e.g., boiling with methanol)
  • (5) Production, quality control, product development, basic research
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35
Q

Describe hydrometry methods of moisture analysis, mentioning (1) principle of method (2) inherent assumptions made (3) sources of error (4) applicability to certain types of foods (5) use as a QC method &/or official method.

A
  • (1) Compare relative density (specific gravity) of sample to than of water at same temperature; hydrometer → based on Archimedes’ principle that a solid suspended in a liquid will be buoyed by a force qual to the weight of the liquid displaced; pycnometer → standardized glassware used to compare weights of equal volumes of a liquid and water
  • (2)
  • (3)
  • (4) Total solute in concentration e.g., brine, sugar in juice, % alcohol, milk solids; limited applications but fast, simple and cheap
  • (5) Quality control
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36
Q

Describe refractive index method of moisture analysis, mentioning (1) principle of method (2) inherent assumptions made (3) sources of error (4) applicability to certain types of foods (5) use as a QC method &/or official method.

A
  • (1) Based on bending of light; the ratio of sines of angle of incidence and refraction; RI determines [compound of interest]
  • (2) temperature and wavelength of light is held constant
  • (3)
  • (4) % alcohol, milk solids, % sucrose in beverages, syrups; limited applications
  • (5) Quality control, product development, basic research
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37
Q

Describe the advantages and disadvantages of dry ashing.

A
  • ADVANTAGES
    • Relatively safe and inexpensive
    • Requires no acids, other reagents, or blanks
    • Can analyze many samples at one time
    • Requires little technician time or attention
    • Resultant ash can be used for some other analyses
  • DISADVANTAGES
    • Long time required to get results (12-18h)
    • Some minerals can be volatilized
    • Some minerals can be hard to resolubilize
    • More expensive than wet ashing
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38
Q

What is the principle of dry ashing?

A

When sample is heated to high temperatures, all organic matter is incinerated, leaving inorganic material to be quantified gravimetrically.

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39
Q

Describe threats to the accuracy and precision of dry ashing. [5]

A
  • Sample preparation & contamination → losses during pre-drying; inorganic contamination
  • Crucibles must be inert & resistant to high temperatures → no binding of minerals; heat-stable e.g., quartz fibre, porcelain, steel, quartz, platinum
  • The ash residue is fluffy and hygroscopic → easy to spill; picks up moisture
  • Volitalization of elements → Fe, Se, Pb, Hg, Cu, Zn, P
  • Incomplete combustion
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40
Q

Describe the principle of wet ashing and describe advantages and disadvantages.

A

Organic matter is oxidized using acids and oxidizing agents, leaving inorganic matter (solubilized)

  • Advantages
    • Minerals stay in solution
    • Less volitilization
    • Short time = few hours
    • Requires only hood, hot plate, long tongs, and safety equipment
  • Disadvantages
    • Requires constant operator attention
    • Can be dangerous (due to corrosive and/or explosive reagents)
    • Handles small numbers of samples
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41
Q

Describe microwave ashing and its advantages, disadvantages.

A
  • Advantages → more rapid than conventional wet or dry ashing; can process many samples at once (though, generally less than with conventional methods)
  • Disadvantages → requires specialized instrumentation = more expensive
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42
Q

Dry-weight basis is always going to be higher than wet-weight basis.

True or False?

A

True.

This is because we are reporting the amount of ash either in relation to the total sample amount including water, or to just the total solids part of the sample.

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43
Q

Wet-weight basis is always going to be higher than dry-weight basis.

True or False?

A

False.

This is because we are reporting the amount of ash either in relation to the total sample amount including water, or to just the total solids part of the sample.

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44
Q

Describe a normal distribution.

A
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45
Q

What is the principle of a forced draft oven as a moisture analysis method?

A

Sample is heated in oven to evaporate water.

Weight loss equals moisture content.

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46
Q

What is the principle of a vacuum oven in moisture analysis?

A

Sample is heated in oven under reduced pressure, so water evaporates at a lower temperature.

Weight loss equals moisture content.

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47
Q

What is the principle of a microwave drying oven for moisture analysis?

A

Sample is heated with microwave energy to evaporate water.

Weight loss equals moisture content.

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48
Q

What is the principle of infrared drying ovens in moisture analysis?

A

Infrared lamp supplies heat that penetrates sample to evaporate water.

Weight loss equals moisture content.

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49
Q

What is the principle of a rapid moisture analyzer?

A

Sample is heated with heating elements to evaporate water.

Weight loss equals moisture content.

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50
Q

What is the principle of reflux distillation (with toluene) in moisture analysis?

A

When sample is heated to toluene (an immiscible liquid), the toluene and water are co-distilled.

Collected moisture distills off, is condensed and collected, and volume of water is measured.

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51
Q

What is the principle of Karl Fischer titration?

A

In titration of sample with Karl Fischer reagent, water in sample reacts with sulfur dioxide to cause reduction of iodine.

Endpoint of titration is detected when excess iodine cannot react with water.

Volume of titrant (i.e., volume of Karl Fischer reagent titrated) is used to calculate % moisture.

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52
Q

What is the principle of a hydrometer?

A

Archimedes’ principle.

Compare relative density (specific gravity) of sample to that of water at same temperature.

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53
Q

How is water removed/reacted/identified & measured in a forced draft oven method?

A

Weight change is measured.

Heat evaporates water when it boils at 100 degrees Celsius.

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54
Q

How is water removed/reacted/identified & measured in a vacuum oven method?

A

Heat sample under reduced pressure to evaporate water at ~70 degrees Celsius.

Weight change is measured.

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55
Q

How is water removed/reacted/identified & measured in a microwave drying oven method?

A

Heat from microwave energy causes water evaporation.

Weight change is measured.

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56
Q

How is water removed/reacted/identified & measured in a infrared drying oven method?

A

Heat from infrared lamp evaporates water.

Weight change is measured.

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57
Q

How is water removed/reacted/identified & measured in a rapid moisture analyzer method?

A

Heat evaporates water when it boils at 100 degrees Celsius.

Weight change is measured.

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58
Q

How is water removed/reacted/identified & measured in a reflux distillation (with toluene) method?

A

Co-distill water from sample with toluene.

Measure the volume of water from sample collected after distillation and condensation.

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59
Q

How is water removed/reacted/identified & measured in a Karl Fischer titration method?

A

Water in sample reacts with iodine and sulfur dioxide to cause reduction of iodine.

Volume of Karl Fishcer Reagent titrated is measured.

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60
Q

How is water removed/reacted/identified & measured in a hydrometer method?

A

Based on solids content of the solution, to determine specific gravity compared to pure water.

Volume displaced by hydrometer is measured. Read specific gravity directly from hydrometer. Measuring solids content.

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61
Q

What cautions/things to control apply to the forced draft oven method of moisture analysis?

A

Control time, temperature; control sample particle size. Must pre-dry some samples to avoid splattering.

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62
Q

What cautions/things to control apply to the vacuum oven method of moisture analysis?

A

Control time and temperature.

Pull and release vacuum slowly.

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63
Q

What cautions/things to control apply to the microwave drying oven method of moisture analysis?

A

Control power and time to prevent sample decomposition. Spread sample evenly. Check calibration and analytical balance.

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64
Q

What cautions/things to control apply to the infrared drying oven method of moisture analysis?

A

Control time and temperature.

Spread sample evenly.

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65
Q

What cautions/things to control apply to the rapid moisture analyzer method of moisture analysis?

A

Control time and temperature.

Spread sample evenly.

Regular calibration of analytical balance.

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66
Q

What cautions/things to control apply to the reflux distillation (with toluene) method of moisture analysis?

A

Any emulsion formed must break to read volume of water.

Need very clean glassware with no water.

Use caution with solvents (fire hazards; toxic).

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67
Q

What cautions/things to control apply to the Karl Fischer titration method of moisture analysis?

A

Control particle size and humidity of room.

Prevent any water in glassware.

Must standardize KRF.

Choose another method if interferences from certain food constituents (e.g., ascorbic acid, carbonyl compounds, unsaturated fatty acids).

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68
Q

What cautions/things to control apply to the hydrometer method of moisture analysis?

A

Control temperature.

Need clean hydrometer.

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69
Q

List advantages and disadvantages of forced draft oven method of moisture analysis.

A

Advantages

  • Easy to handle many samples at one time.

Disadvantages

  • Takes long time to get results.
  • High temperature can cause loss of volatiles, lipid oxidation, Maillard browning, sucrose hydrolysis (not suitable for some foods).
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70
Q

List advantages and disadvantages of vacuum oven method of moisture analysis.

A

Advantages

  • Easy to handle many samples at one time.
  • Lower temperature for evaporating water reduces problems associated with high-sugar products.

Disadvantages

  • Takes long time to get results (though usually less time than with a forced draft oven).
  • More expensive than forced draft oven.
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71
Q

List advantages and disadvantages of microwave drying oven method of moisture analysis.

A

Advantages

  • Rapid.

Disadvantages

  • More expensive than other drying methods.
  • Can only run one sample at a time.
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72
Q

List advantages and disadvantages of infrared drying oven method of moisture analysis.

A

Advantages

  • Rapid.

Disadvantages

  • Expensive.
  • Can only run one sample at a time.
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73
Q

List advantages and disadvantages of rapid moisture analyzer method of moisture analysis.

A

Advantages

  • Rapid

Disadvantages

  • Expensive.
  • Can only run one sample at a time.
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74
Q

List advantages and disadvantages of reflux distillation (with toluene) method of moisture analysis.

A

Advantages

  • Causes less thermal decomposition in some foods than oven drying.
  • Solvent protects sample from losing volatiles and minimizes oxidation.
  • Water is measured directly.

Disadvantages

  • Can only run one sample at a time.
  • Solvent is likely flammable and toxic.
  • Reading volume of water in receiving tube may be less accurate than gravimetric methods.
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75
Q

List advantages and disadvantages of Karl Fischer titration method of moisture analysis.

A

Advantages

  • No heat, so no thermal decomposition.
  • Rapid.
  • Higher accuracy than many other methods for low-moisture foods.

Disadvantages

  • Can only run one sample at a time.
  • Expensive, if using automated unit.
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76
Q

List advantages and disadvantages of hydrometer method of moisture analysis.

A

Advantages

  • Rapid.
  • Easy.
  • Inexpensive.

Disadvantages

  • Limited applications.
  • Measures only solids content.
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77
Q

Forced draft oven drying for moisture analysis is the official method for many types of samples.

Describe when draft oven drying is not suitable.

A

Not suitable for rapid quality control results.

Not suitable for samples subject to loss of volatiles, lipid oxidation, Maillard browning, or sucrose hydrolysis.

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78
Q

Describe typical applications of the vacuum oven drying method.

A

An official method for many types of products.

Not suitable for rapid quality control.

Not suitable for powdered products, since they can blow around when vacuum is pulled and released.

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79
Q

Describe typical applications of the microwave drying oven drying method.

A

Suitable for rapid quality control, especially for liquid products, since use of pads avoids splattering.

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80
Q

Describe typical applications of the infrared drying oven drying method.

A

Suitable for rapid quality control, but not for high moisture products (would get splattering).

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81
Q

Describe typical applications of the rapid moisture analyzer method.

A

Suitable for rapid quality control, but not for high moisture products (would get splattering).

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82
Q

Describe typical applications of the reflux distillation (with toluene) method.

A

AOAC method for spices.

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83
Q

Describe typical applications of the Karl Fischer titration method.

A

Method of choice of many low-moisture foods (e.g., dried fruits and vegetables, candies, chocolate, roasted coffee, oils and fats, and many low-moisture foods that are high in sugar or protein).

Good method to try if method with heating and/or vacuum gives erratic results.

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84
Q

Describe typical applications of the hydrometer method.

A

Commonly used as rapid method to measure solids content of beverages, salt brines, and sugar solutions.

Best applied to solutions with only one solute in a medium of water.

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85
Q

Discuss the importance of fat in foods.

A
  • Nutrition
    • Major source of energy.
    • Carrier of vitamins (A, D, E, K)
    • Source of essential fatty acids.
  • Physical properties
    • Texture
    • Mouthfeel
    • Flavour
    • Heat transfer / cooking medium
  • Stability/shelf-life
    • Oxidation; rancidity
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86
Q

What do the terms ‘fat’ / ‘lipids’ / ‘oils’ include?

A
  • Simple lipids → fatty acid esters of alcohols (TAG, DAG, MAG, waxes)
  • Compound lipids → fatty acid esters of alcohols + other groups (e.g., phospholipids)
  • Derived lipids → fatty acids, long-chain alcohols, sterols, fat-soluble vitamins
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87
Q

What is the working definition of fats for proximate analysis?

A

Insoluble in water & soluble in organic solvents

Lipids = in general, are soluble in ether, chloroform, acetone, ethanol, benzene, hexane, etc., but are sparingly soluble in water.

FDA’s regulatory definition of ‘total fat’ for nutrition labelling purposes = sum of fatty acids from C4 to C24, calculated as triglycerides (e.g., include weight of glycerol per 3 FA)

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88
Q

Describe the principle of solvent fat extraction methods, and list 3 general considerations.

A
  • Principle → fat is extracted with solvent; fat content is measured by weight loss of sample or by weight of fat removed
  • Considerations
    • What type of solvent should be used?
    • Sample type (requires dry samples)
    • Bound fat (lipoproteins, liposaccharides)
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89
Q

Why does solvent fat extraction require dry samples? What other considerations are important for this method?

A

Nonpolar solvents cannot penetrate wet samples.

  • Require dry samples for solvent extraction
  • Drying conditions are important
  • Particle size reduction may also be required.
  • The polarity of the solvent used for extraction influences the type of fat extracted.
  • Alternatively, use non-solvent methods for wet samples.
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90
Q

Why are samples pre-dried in solvent fat extraction methods?

A
  • Pre-drying sample:
    • Makes sample easier to grind
    • Breaks fat-water emulsion to more easily dissolve fats in organic solvent
    • Helps release lipids from food tissue.
    • Solvent extraction requires dry samples because nonpolar solvents. cannot penetrate wet samples.
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91
Q

Describe ethyl ether.

A
  • Organic nonpolar solvent.
  • BP = 34.6 degrees Celsius
  • Generally a better solvent for fat
  • More expensive
  • Greater danger of explosion and fire hazard
  • Hygroscopic
  • Forms peroxides
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92
Q

Describe petroleum ‘ether’.

A
  • Not actually an ether!
  • BP ~30-80 degrees Celsius
  • Selective for more hydrophobic lipids
  • Cheaper
  • Less hydroscopic
  • Less flammable
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93
Q

How may bound fat be extracted?

A

Acid and/or alkaline hydrolysis to break interactions between proteins &/or carbohydrates

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94
Q

Why is it necessary to reduce particle size in fat solvent extraction?

A

Increases extraction efficiency

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95
Q

Describe the Goldfisch fat extraction method.

A

Continuous solvent extraction

  • Procedure
    • Dry sample in porous thimble; solvent in pyrex beaker
      • Extract with solvent
      • Mass loss = fat content &/or
      • Collect solvent
      • Evaporate solvent
      • Weigh the fat
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96
Q

What are advantages and issues with Goldfisch continuous solvent extraction?

A

Advantages

  • Efficient, fast (4 hours or so)
  • Multiple samples

Issues

  • Channeling
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97
Q

Describe the Soxhlet fat extraction method.

A

Semi-continous solvent extraction

  • Procedure
    • Extract with solvent
    • Mass loss = fat content &/or
    • Collect solvent
    • Evaporate solvent
    • Weigh the fat
  • Difference from Goldfisch → solvent pools around the sample, then siphons back to boiling flask
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98
Q

Describe advantages and disadvantages with Soxhlet solvent extraction.

A

Advantages

  • More complete extraction
  • Less chance of ‘channeling’ than continuous solvent extraction

Disadvantage

  • Slower (16 hours or so)
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99
Q

Describe alkaline hydrolysis (a.k.a. Mononnier fat) extraction method.

A

Discontinuous solvent extraction

  • Procedure
    • Treat sample, in series, with:
      • Ammonium hydroxide → precipitate proteins
      • 95% ethanol → prevents gelation
      • Ethyl ether, then petroleum ether
    • Decant ether layer → contains fat
    • Repeat extraction series
    • Evaporate solvent
    • Weigh fat
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100
Q

What are advantages of alkaline hydrolysis (a.k.a. Mojonnier fat) extraction? What is it mainly used for?

A
  • Simple/low cost
  • Moisture removal from sample is not necessary
  • Used mainly for dairy products (proteins surround milk globules → precipitate proteins = easier to extract fat)
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101
Q

Describe acid hydrolysis fat extraction method.

A

Discontinuous solvent extraction

  • Procedure
    • Treat sample with HCl → free lipids from protein or carbohydrate
    • Extract with ethyl ether then petroleum ether
    • Decant ether layer → contains fat
    • Repeat extraction series
    • Evaporate solvent
    • Weigh fat
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102
Q

What are advantages of acid hydrolysis for fat extraction?

A
  • Moisture removal from sample not necessary.
  • Simple/low cost
  • Used for many products.
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103
Q

What is done after alkaline or acid hydrolysis?

Describe its method & application.

A

GC analysis → solvent extraction + quantify lipids using gas chromatography = official method for nutrition labelling.

  • Procedure
    • Add internal standard (e.g., known amount of specific fatty acid)
    • Add antioxidant (to limit lipid oxidation)
    • Acid/alkaline hydrolysis procedure
    • Extract lipids with ethyl ether, petroleum ether
    • Derivatize fatty acids (add methyl group) = fatty acid methyl esters (FAMEs) → makes them volatile
    • Separate and quantify using gas chromatography (i.e, areas under peaks)
    • Total fat = sum of individual FAMEs
    • Area under the curve is proportional to the amount of fatty acid present in sample.
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104
Q

Why does vitamin C lead to an overestimation of moisture content in the Karl Fischer titration method of moisture analysis?

A

Ascorbic acid reduces the Karl Fischer reagent.

Ascorbic acid undergoes a redox reaction with the KFR. Ascorbic acid reduces I2 → 2I- (in turn, ascorbic acid is oxidized).

During a KF titration, ascorbic acid uses up I2, effectively prolonging the end point leading to the overestimation of the water content.

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105
Q

Describe the chloroform-methanol (‘Folch’ or ‘Bligh/Dyer’) fat extraction method.

A

Discontinuous solvent extraction

  • Procedure
    • Sample is mixed/homogenized in chloroform-methanol solution, then filtered.
    • Potassium chloride is added to break solution into two phases: aqueous and chloroform (contains fat)
    • Isolate chloroform layer (separatory funnel; centrifuge)
    • Evaporate chloroform
    • Weigh fat.
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106
Q

What are advantages of the chloroform-methanol (‘Folch’ or ‘Bligh/Dyer’) fat extraction method?

A
  • Moisture removal from sample not necessary
  • Well suited to samples of low fat content
  • Simple/low cost
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107
Q

Describe the Babcock method of fat extraction.

A

Non-solvent wet extraction

  • Procedure
    • Sulfuric acid digests protein, generates heat, and releases fat
    • Add water
    • Centrifugre samples → fat separates to top
    • Fat content is measured volumetrically
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108
Q

What are advantages of the Babcock method of fat extraction?

A
  • Moisture removal from sample not necessary
  • Mainly used for determining milk fat; also fat in seafood.
  • Simple method.
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109
Q

Describe the Gerber method of fat extraction.

A

Non-solvent wet extraction

  • Procedure
    • Sulfuric acid and amyl alcohol digests protein, generates heat, and releases fat.
    • Centrifuge samples
    • Fat content is measured volumetrically.
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110
Q

What are advantages of the Gerber method of fat extraction?

A
  • Moisture removal from sample not necessary
  • Mainly used for determining milk fat
  • Simple method
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111
Q

Which fat extraction method is often viewed as a standard method for ‘crude’ fat determination?

A

Soxhlet - but need to dry samples.

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112
Q

What is the official method of fat extraction for nutrition labelling?

A

Gas chromatography.

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113
Q

Discuss the importance of protein.

A
  • Nutrition labelling (total protein content)
  • Quality control & product development
  • Pricing (e.g., cereal grains, milk products) → fat & protein = high value commodities
  • Functional property investigation
  • Biological activity determination (e.g., enzymes, enzyme inhibitors, allergens → so can express as % of total protein)
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114
Q

Discuss the functionality of protein in food.

A
  • Physical, chemical properties
    • Provide structure (bulk, texture, viscosity)
    • Stabilize gels, foams, emulsions
    • Add flavour, aroma (amino acids)
  • Other important functions/features:
    • Nutrition
    • Bioactivity (hormones, allergens)
    • Enzyme activity (spoilage, processing, assays for safety/quality)
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115
Q

Discuss protein structure & properties

A
  • Primary, secondary, tertiary, quaternary structures
  • Polypeptide → linear change of L-amino acids connected via amide/peptide bonds
  • Peptide backbone = relatively hydrophilic
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116
Q

What are the protein features used in protein extraction? [4]

A
  • Nitrogen content = unique among major food components (water, CHO, fat, ash)
  • Dye binding capacity = charged groups, hydrophobic pockets, peptide backbone
  • Peptide bonds = amide groups = characteristic IR and UV absorption
  • Aromatic amino acids = characteristic UV absorption
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117
Q

What are the AOAC official methods for protein analysis? [3]

A
  1. Total nitrogen → Kjeldahl (acid digestion); Dumas (nitrogen combustion)
  2. Spectroscopic methods → Infrared spectroscopy (peptide bonds)
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118
Q

List the methods for protein analysis that are mostly used for research.

A
  1. Colorimetric methods → anionic dye binding (dye binding to basic a.a.); Bradford assay (dye-binding by amino acid side chains); Biuret, Lowry, & bicinchoninic acid (BCA) assays (based on reaction of peptide bonds with copper)
  2. Spectroscopic methods → UV absorbance (peptide bond, aromatic residues)
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119
Q

Describe the principle of the Kjeldahl method. [4]

A

Determine the amount of nitrogen in a sample by (1) acid digestion to release N as NH4+, (2) neutralization to convert NH4+ → NH3, simultaneous with distillation to isolate NH3, (3) titration to quantify the NH3, and (4) calculate the %N and relate to %protein using a conversion factor.

Catalyst = CuSO4, or others

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120
Q

Describe the Kjeldahl method procedure & assumptions.

A
  1. Digestion with acid → H2SO4, catalyst, heat (>370 degrees Celsius), releases N as NH4+
  2. Neutralization & distillation → base added = generates NH3, distill & collect in solution of boric acid
  3. Titration → NH3 + boric acid → borate ion (blue/red indicator); titrate borate ion + HCl → boric acid (pale grey)
  4. Calculation → moles HCl required to titrate borate ion = moles N

Assumptions → All N derived from protein (includes all organic N)

The amount of borate produced is equivalent to the amount of ammonia that is derived from the protein in the sample. Borate is titrated with HCl back to boric acid in order to quantify (blue-red → pale grey). Measurable is how much HCl is needed to titrate the borate.

The method consists essentially of transforming all nitrogen in a weighed sample into ammonium sulfate by digestion with sulfuric acid, alkalizing the solution, and determining the resulting ammonia by distilling it into a measured volume of standard acid, the excess of which is determined by titration.

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121
Q

What is the calculation for %N in the Kjeldahl method?

A

Conversion factors vary between different proteins, due to differences in amino acid composition.

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122
Q

Describe the principle of the Dumas method of protein analysis. What is the assumption of this method?

A

Convert sample N to N2 by combustion, then measure using gas chromatography.

Assumption = All N is derived from protein (includes organics & inorganics/nitrates)

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123
Q

Describe the Dumas method procedure.

A
  1. Convert protein nitrogen to N2 (&NOx) by flash combustion at 700-1000 degrees Celsius → NOx compounds are converted to N2 by combustion
  2. Determine N2 by gas chromatography & thermal conductivity detector → integrate area under the curve to tell you then amount of N
  3. Convert N content to protein content using a conversion factor.
  4. Results in only a few minutes.
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124
Q

Compare Kjeldahl & Dumas protein analysis methods.

A
  • Both:
    • Official methods for crude protein
    • Applicable to all types of food
    • Measure total nitrogen (not only protein N) = possible to spike foods with N-rich chemicals (e.g., Melamine adulturation)
    • Requires correct %N → %protein conversion factor
  • Differences
    • Kjeldahl = corrosive reagents, environmental concerns, time-consuming, technical expertise required
    • Dumas = fast, little attention required if using automated instrument, but expensive!
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125
Q

How can non-protein nitrogen be measured?

A

Isolate proteins by precipitation (e.g.,using TCA) & perform analysis on remaining non-protein nitrogen

  • Procedure
    • To sample, add TCA (trichloroacetic acid) to 10% m/v final concentration [or, dissolve dry sample into 10% TCA solution]
    • Proteins denature & precipitate
    • Filter or centrifuge sample to remove protein pellet
    • Proceed with analysis (Kjeldahl, Dumas) of supernatant
    • Any nitrogen = non-protein nitrogen
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126
Q

What is the principle of anionic dye binding for protein analysis?

A

Dye-binding induces protein precipitation; remove protein precipitate and measure [dye] in the supernatant. The [unbound dye] is inversely proportional to [protein]

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127
Q

Describe the procedure of anionic dye binding method of protein analysis.

A
  1. Dye binds protein basic amino acids (His, Arg, Lys) and free terminal amino group of protein = causes protein to precipitate
  2. Remove protein-dye precipitate (spin, or filter)
  3. Quantify the unbound [dye]
  4. Calculate [dye]-bound to protein
  5. Relate [dye]protein-bound to [protein] using a calibration curve → Kjeldahl or Dumas analysis
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128
Q

Describe the procedure of anionic dye binding method of protein analysis.

A
  1. Dye binds protein basic amino acids (His, Arg, Lys) and free terminal amino group of protein = causes protein to precipitate
  2. Remove protein-dye precipitate (spin, or filter)
  3. Quantify the unbound [dye]
  4. Calculate [dye]-bound to protein
  5. Relate [dye]protein-bound to [protein] using a calibration curve → Kjeldahl or Dumas analysis
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129
Q

Describe the principle of the Bradford assay.

A
  • Dye (Coomassie Brilliant Blue G-250) binds to proteins via basic and aromatic side chains, particularly Arginine (and Phe, Trp, Tyr)
  • Max wavelength shifts from 465nm to 595nm upon binding protein
  • Measure absorbance at 595nm and relate to [protein] using a calibration curve.
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130
Q

Describe the procedure for the Bradford assay.

A
  • Prepare a series of standards of increasing concentration e.g., BSA solutions from 0.1 → 1.0 mg/mL
  • Mix the standards with dye solution (acidic pH)
  • Mix the sample with dye solution (acidic pH)
  • Measure absorbance at 595nm
  • Calibration curve: plot A595nm vs [BSA]
  • Calculate [sample] using the calibration curve
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131
Q

What is the major issue with the Bradford assay?

A

Variability in how dye binds to different proteins.

BSA most often used as a standard.

Ideally = use purified form of protein of interest e.g., if we want to quantify [ovalbumin], use ovalbumin as standard.

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132
Q

What is the general principle of colorimetric methods involving reactions with copper?

A
  • Under alkaline conditions, Cu2+ binds to proteins giving rise to a colour change
  • Increase in VIS absorbance proportional to [protein]
  • Use calibration curve (e.g., BSA)
  • Absorbance measured at
    • Biuret - 540nm
    • Lowry - 650-750nm
    • BCA - 562nm
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133
Q

What does cuprous ion bind to give a purple colour?

A

BCA

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134
Q

What does IR measure?

A

Vibrational transitions

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135
Q

What are advantages and limitations of UV absorbance?

A

Advantages

  • Accurate if extinction coefficient is accurate (experimental, calculate)
  • Non-destructive
  • Rapid

Disadvantages

  • Requires pure and clear solution
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136
Q

What is the principle and procedure of UV absorbance method of protein analysis?

A
  • Principle
    • Trp and Tyr absorb UV light at ~280nm
    • [protein] proportional to absorbance at 280nm
  • Procedure
    • Measure A280 of blank (e.g., buffer)
    • Measure A280 of sample; subtract blank
    • Calculate [protein] using Beer-Lambart law
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137
Q

Describe the principle and application of IR spectroscopy for protein analysis.

A
  • Principle
    • Different functional groups give characteristic absorption of IR light
    • Peptide bond gives absorption bands in the mid (6500nm) and near-IR (3300, 2200, 1600nm) regions
    • Requires a calibration curve (i.e., relies on other methods)
  • Application:
    • Rapid, on-line analysis
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5
Perfectly
138
Q

Summarize the methods for protein analysis.

A
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139
Q

What is the chemical basis and principle of the Kjeldhal method?

A

Nitrogen (total organic)

Determine N by method that involves digestion, neutralization, distillation, and titration.

Use N content to calculate protein content.

140
Q

What is the chemical basis and principle of the Dumas method?

A

Nitrogen (total organic and inorganic)

N is released upon combustion of sample at very high temperature.

N gas is quantitated by gas chromatography using a thermal conductivity detector.

Use N content to calculate protein content.

141
Q

What is the chemical basis and principle of the Infrared Spectroscopy method?

A

Peptide bond

Presence of peptide bond in protein molecules causes absorption of radiation at specific wavelength in mid-or near-IR region

142
Q

What is the chemical basis and principle of the Anionic dye-binding method?

A

Basic amino acid residues (of histidine, arginine, and lysine), and N-terminus of protein molecule.

Residues identified react with anionic sulfonic acid dye to form an insoluble complex.

Unbound soluble dye is measured by absorbance and related to protein concentration.

143
Q

What is the chemical basis and principle of the bicinchoninic acid (BCA) method?

A

Peptide bond and specific amino acids (cystein, cystine, tryptophan, and tyrosine)

Peptide bond is complexed with cupric ions under alkaline conditions.

Cuprous ions are chelated by BCA reagent to give colour measured by spectroscopy.

144
Q

What is the chemical basis and principle of the Biuret method?

A

Peptide bond

Peptide bond is complexed with cupric ions under alkaline conditions to give colour that is quantitated by spectroscopy.

145
Q

What is the chemical basis and principle of the absorbance at 280nm method?

A

Tyrosine and tryptophan

Aromatic amino acids, tryptophan and tyrosine, cause proteins to absorb at 280nm.

Absorbance can be used to estimate protein content.

146
Q

What is the chemical basis of absorbance at 220nm method?

A

Peptide bond

Peptide bonds cause proteins to absorb at 220nm.

Absorbance can be used to estimate protein content.

147
Q

What are advantages and disadvantages of the Kjeldahl method?

A

Advantages

  • Inexpensive (if not automated system)
  • Widely used and accepted method for over a century.

Disadvantages

  • Measures total organic nitrogen and not just protein N.
  • Uses corrosive reagents.
  • Lower precision than some other methods.
148
Q

What are advantages and disadvantages of the Kjeldahl method?

A

Advantages

  • Inexpensive (if not automated system)
  • Widely used and accepted method for over a century.

Disadvantages

  • Measures total organic nitrogen and not just protein N.
  • Uses corrosive reagents.
  • Lower precision than some other methods.
149
Q

What are advantages and disadvantages of the Dumas method?

A

Advantages

  • Requires no hazardous chemicals.
  • Rapid (few minutes).
  • Automates instruments allow for analyzing many samples without attention.

Disadvantages

  • Expensive equipment.
  • Measures total organic and inorganic N, and not just protein N.
150
Q

What are advantages and disadvantages of the Infrared spectroscopy method of protein analysis?

A

Advantages

  • Rapid way to estimate protein content.
  • Requires minimal training.

Disadvantages

  • Expensive equipment.
  • Only provides an estimate of protein content.
  • Instrument must be calibrated against results of official methods.
151
Q

What are advantages and disadvantages of the anionic dye-binding method?

A

Advantages

  • Rapid (15 mins or less)
  • Relatively accurate.
  • No corrosive reagents.
  • Does not measure non-protein N.
  • More precise than Kjeldahl method.
  • Can be used to estimate changes in available lysine content, since the dye does not bind altered, unavailable lysine.

Disadvantages

  • Not as sensitive as some other colorimetric methods.
  • Requires a calibration curve for a given food commodity, since foods differ in basic amino acid content and so differ in dye-binding capacity.
  • Not suitable for hydrolyzed proteins due to dye binding to N-terminal amino acids.
  • Some non-protein components bind dye or protein, to cause error.
152
Q

What are advantages and disadvantages of the Bicinchoninic acid (BCA) method?

A

Advantages

  • Good sensitivity, and micro-BCA method is even better.
  • Nonionic detergents and buffer salts do not interfere with the reaction, nor do medium concentrations of denaturing reagents.

Disadvantages

  • Colour is not stable with time.
  • Any compound capable of reducing Cu2+ to Cu+ will lead to colour formation.
  • Reducing sugars and high concentrations of ammonium sulfate interfere.
  • Get colour variation among proteins.
153
Q

What are advantages and disadvantages of the absorbance at 280nm method?

A

Advantages

  • Rapid
  • Relatively sensitive.
  • No interference from ammonium sulfate and other buffer salts.
  • Nondestructive (So samples can be used after protein determination)

Disadvantages

  • Nucleic acids can absorb at 280nm.
  • Aromatic amino acid contents in proteins vary between food sources, so results are qualitative.
  • Requires relatively pure, clear, and colourless samples.
154
Q

What are advantages and disadvantages of the absorbance at 220nm method?

A

Advantages

  • Rapid
  • Nondestructive (so samples can be used after protein determination)

Disadvantages

  • Many things other than peptide bonds absorb at 220nm.
  • Requires relatively pure, clear, and colourless samples.
155
Q

What are advantages of the Biuret method?

A

Advantages

Less expensive, faster, and simpler than Kjeldahl method

Does not detect non-peptide sources

Few interferences.

156
Q

What are applications of the Kjeldahl method?

A

Applicable to all foods.

Little use now, due to availability of automated Dumas systems.

157
Q

What are applications of the Dumas method?

A

Applicable to all foods.
Widely used now, compared to Kjeldahl method, for both official and quality control purposes.

158
Q

What are applications of the IR spectroscopy method?

A

Applicable to wide range of food products (grains, cereal, meat, dairy).

Used as a rapid, quality control method.

159
Q

What are applications of the anionic dye-binding method?

A

Automated version used for quality-control purposes, especially as a method to compare results against a nitrogen-based method (to check for economic adulturation).

160
Q

What are applications of the Bicinchoninic acid (BCA) method?

A

Widely used method for protein isolation and purification.

Has largely replaced other quantitative research colorimetric methods.

161
Q

What are applications of the absorbance at 280nm method?

A

Best used in purified protein systems (e.g., postcolumn detection of intact proteins)

162
Q

What are applications of the absorbance at 220nm method?

A

Best used with purified hydrolyzed protein systems (e.g., postcolumn detection of hydrolyzed proteins)

163
Q

You are considering the use of a new method to measure compound X in your food product. List six factors you will consider before adopting this new method in your quality assurance laboratory.

A
  • Validity of the method e.g., representative sample? reproducible results?
  • Applicability to the lab e.g., cost of assay, equipment, reagents required
  • Inherent properties e.g., specificity, precision, accuracy, sensitivity, sample size required
  • Usefulness e.g., time required, speed, reliability, necessity
  • Personnel e.g., safety, training, competency, procedures
164
Q

Which method is more precise? Which is more accurate?

A

Method A is more precise because the data has a smaller standard deviation from the mean compared to Method B. This implies that method A has a greater replicability than method B. This is because the smaller the standard deviation, the more likely the result is to match the target value.

Method B is more accurate because its mean is closer to the true value than Method A’s mean.

165
Q

Is absolute error more useful than relative error?

A

Relative error is more useful → the absolute error relative to the true value

Absolute error → the difference between the experimental mean and the true value; typically, not as informative as relative error

166
Q

Classify the error and describe a way to fix it.

Automatic pipettor consistently delivered 0.96mL rather than 1.00mL

A

Systematic error

Account for the systematic error by calibrating the pipettor

167
Q

Classify the error and describe a way to fix it.

Substrate was not added to one tube in an enzyme assay.

A

Blunder

Redo assay, be more careful.

168
Q

Differentiate between sensitivity and limit of detection.

A

Sensitivity → magnitude of change in measurement with change in concentration of compound; a more sensitive instrument requires a smaller change in concentration of the compound to have a large response; a less sensitive instrument requires a larger change in concentration of the compound to have a small response. Lower sensitivity method may be preferred in certain scenarios, however.

Limit of detection → lowest amount to detect with statistical significance; the mean of the blank sample plus three times its standard deviation.

169
Q

Identify five factors that one would need to consider when choosing a moisture analysis method for a specific food product.

A
  • What is measured?
  • How is the water removed/reacted/identified?
  • Assumptions?
  • Sources of error?
  • Applications?
  • Expected moisture content
  • Nature of other food constituents
  • Equipment available
  • Speed necessary
  • Intended purpose
170
Q

What are the potential advantages of using a vacuum oven rather than a forced draft oven for moisture content determination?

A

Drying under lower pressure allows a lower temperature and a faster process. The lower temperature helps to mitigate issues associated with decomposition of the sample. By drying under reduced pressure, more complete removal of water and volatiles can be achieved at a lower temperature and without decomposition in a shorter period than with a forced draft oven.

171
Q

Is moisture content over or underestimated?

Forced draft oven - particle size too large

A

Underestimate; potentially water is entrapped within the food particle and the sample is not entirely dry; water in interior of particles will not be volatized

172
Q

Is moisture content over or underestimated?

Forced draft oven - high concentration of volatile flavour compounds present

A

Overestimate; some of the weigh difference between the wet and dry samples will be due to the loss of the volatile flavour compounds; weigh loss due to volatiles will be assumed as water

173
Q

Is moisture content over or underestimated?

Forced draft oven - lipid oxidation

A

Underestimate; sample has weight gain due to peroxide formation

174
Q

Is moisture content over or underestimated?

Forced draft oven - sample very hygroscopic

A

Overestimate; if the sample is retaining or acquiring water at any point during the measurements then error could be introduced; if moisture absorbed before initial weighing; measure water absorbed as moisture in product

Underestimate; if moisture absorbed after drying and before final weighing

175
Q

Is moisture content over or underestimated?

Forced draft oven - alteration of carbohydrates (e.g., Maillard browning)

A

Overestimate; a reducing sugar dehydrates an amino group (which usually comes from protein) and along the biochemical pathway water molecules are generated; the chemical generation of ‘new water’ means an overestimation

176
Q

Is moisture content over or underestimated?

Forced draft oven - sucrose hydrolysis

A

Underestimate; water is a reactant and is incorporated into the sucrose hydrolysis products, so for every molecule of sucrose hydrolyzed a molecule of water is lost that cannot be measured; this water will not be removed by drying as it has become incorporated into the monosaccharides; water is being used in the chemical reaction

177
Q

Is moisture content over or underestimated?

Forced draft oven - surface crust formation

A

Underestimate; water becomes trapped within interior of the sample because the crust prevents its evaporation; cannot remove residual water from under crust

178
Q

Is moisture content over or underestimated?

Forced draft oven - splattering

A

Overestimate; loss of sample due to splattering treated as water loss

179
Q

Is moisture content over or underestimated?

Forced draft oven - desiccator containing desiccant with dried sample not sealed properly

A

Underestimate; the desiccant is likely to exchange moisture with the environment towards equilibrium, meaning the desiccant will be affected by exposure to environmental humidity levels; increase weight of dried samples due to moisture absorption from environment

180
Q

Is moisture content over or underestimated?

Toluene distillation - emulsion between water in sample and solvent not broken

A

Underestimate; water trapped in the solvent layer will not be measured along with the rest of the water; water will not be released from emulsion and measured.

181
Q

Is moisture content over or underestimated?

Toluene distillation - water clinging to condenser

A

Underestimate; water trapped on the condenser cannot be measured

182
Q

Is moisture content over or underestimated?

Karl Fischer - Very humid day when weighing original samples

A

Overestimate; humidity from the environment may adhere to apparatus and facilitate the reduction of iodine by sulfur dioxide

183
Q

Is moisture content over or underestimated?

Karl Fischer - glassware not dry

A

Overestimate; water on glassware can extend the titration endpoint

184
Q

Is moisture content over or underestimated?

Karl Fischer - Sample ground coarsely

A

Underestimate; sample will be trapped in the large particles and be unavailable to react

185
Q

Is moisture content over or underestimated?

Karl Fischer - Food high in vitamin C

A

Overestimate; ascorbic acid reduces Karl-Fischer reagent and extends titration endpoint

186
Q

Is moisture content over or underestimated?

Karl Fischer - food high in unsaturated fatty acids

A

Overestimate; unsaturated fatty acids react with iodine

187
Q

Moisture analysis - liquid ice cream mix - quality control.

Method?

Principle?

Justification?

Cautions?

A
  • Method → Hydrometer
  • Principle → Archimedes’ principle; yields specific gravity
  • Justification → Simple, fast, and cheap form of quality control
  • Cautions → Construction of standard curve needs to be reliable and valid
188
Q

Moisture analysis - milk chocolate - official

Method?

Principle?

Justification?

Cautions?

A
  • Method → chemical titration
  • Principle → Sample with KFR reacts with sulfur dioxide to reduce iodine; endpoint of titration is detected when no water remains to react with excess iodine
  • Justification → good for low moisture foods
  • Cautions → control humidity of the environment; control particle size; prevent water in glassware
189
Q

Moisture analysis - spices - official

Method?

Principle?

Justification?

Cautions?

A
  • Method → distillation
  • Principle → water from sample and immiscible liquid are co-distilled.
  • Moisture distills off, is condensed, collected, and volume measured.
  • Justification → AOAC method for spices
  • Cautions → emulsions must break to read volume of water; need clean glassware with no water; use caution with solvents
190
Q

Moisture analysis - syrup for canned peaches - quality control

Method?

Principle?

Justification?

Cautions?

A
  • Method → refractive index method
  • Principle → based on the bending of light; the ratio of sines of the angle of incidence and refraction
  • Justification → good option to measure sugar content in syrup
  • Cautions → keep temperature and wavelength of light constant; ensure valid and reliable construction of the standard curve
191
Q

Moisture analysis - oat flour - quality control

A
  • Methods → NIR or rapid moisture analyzer
192
Q

You are a manufacturer of processed cheese. The maximum allowed moisture content for your product is 40%. Your current product has a mean moisture content of 38%, with a standard deviation of 0.7. It would be possible to increase your mean moisture content to 39.5% if you could reduce your standard deviation to 0.25. This would result in a saving of $3.4 million per year. You can accomplish this by rapidly analyzing the moisture content of the cheese blend prior to the cooking step of manufacture. The cheese blend is prepared in a batch process, and you have 10 min. to adjust the moisture content of each batch.

Describe the rapid moisture analysis method you would use and your rationale. How would you ensure accuracy and precision of this method?

A

Many methods would work (e.g., rapid moisture analyzer) but microwave oven is an example of a good choice here because it is simple, accurate, and can be performed in about 3 minutes (sufficient for given scenario).

Accuracy and precision could be ensured by comparing the results to a primary method and run known reference standards (daily). Additionally, the standard deviation and coefficient of variation of the method needs to be determined to ensure it falls within required ranges.

193
Q

Identify four potential sources of error in the preparation of samples for ash analysis, and ways to overcome each.

A
  • Sample not representative → develop a statistically valid sampling plan; homogenize sample
  • Microelement contamination → clean glassware and porcelain crucibles by soaking in acid; adjust grinder properly to prevent the appearance of metal shavings in samples; avoid exposing samples to metals in the lab; use deionized-distilled water
  • Sample residue carryover from previous samples → pre-ash crucibles to assure complete removal of organic material from previous samples
  • Sample loss during pre-ashing drying step → slowly ramp up the temperatures to prevent splattering of samples with high moisture content
194
Q

You are determining total ash content of a product using the conventional dry ashing method. Your boss asks you to switch to a conventional wet ashing method because it is faster. Do you agree?

A

Yes & No.

Dry ashing takes more total time to obtain results, but much less technician time and less constant attention than wet ashing.

Also, wet ashing is not used to determine %ash, so this is misleading. Tell the boss yes overall wet ashing is faster, but it is not useful for %ash. If speed is important, we need to buy a microwave instrument for dry ashing.

195
Q

What are advantages of dry ashing?

A

Relatively safe

Requires no acids/oxidizers (as wet ashing does)

Requires no blank subtraction

Requires little attention

Can handle large number of samples at once

Can use ashed sample for several other analyses

196
Q

What are advantages of wet ashing?

A

Minerals usually stay in solution

Little or no loss from sample volatization

Does not require a muffle furnace (which is expensive)

197
Q

Your lab technician was to determine the ash content of buttermilk by conventional dry ashing. The technician weighed 5 g of buttermilk into one weighed platinum crucible, immediately put the crucible into the muffle furnace using a pair of all stainless steel tongs, and ashed the sample for 48 h at 800°C. The crucible was removed from the muffle furnace and set on a rack in the open until it was cool enough to reweigh.

What errors were made in the preceding method (there were several)?

What were the likely results of the errors?

What instructions should you have given your technician before starting the procedure in order to avoid the errors you noted?

A
  • Testing just one sample → inaccurate result
  • No drying of sample before ashing → splattering of sample in oven
  • Not using platinum-tip tongs to handle crucible → iron/chromium contamination
  • Ashed for excessively long time and at too high a temperature → volatilization of some minerals
  • Didn’t place ashed samples in desiccator to cool before weighting → samples would absorb moisture

Instructions

  1. Number of replicates to analyze
  2. How to treat liquid samples before ashing
  3. How to handle crucibles before and after ashing (i.e., type of tongs)
  4. time and temperature for ashing (12-18 hours at 500-600 degrees Celsius)
  5. How to cool crucibles coming from muffle furnace prior to weighing
198
Q

How would you over come volatilization of phosphorus during dry ashing when you later want to determine phosphorus content?

A

Lower the temperature or use a wet-ashing procedure instead

199
Q

How would you overcome incomplete combustion of a product high in sugar after a typical dry ashing procedure?

A

After initial ashing, solubilize ash in water, then filter (with ash-less filter paper) to separate soluble ash from insoluble ash. Re-ash each portion separately (after drying soluble ash). Make sure to separately ash a piece of ash-less filter paper. This will serve as a blank for correction of insoluble ash sample. Combined the weight of soluble and insoluble to get final ash weight.

200
Q

If a typical dry ashing procedure takes too long for your purpose, but you do not want to use wet ashing, how can you fix this?

A

Use microwave dry-ashing

201
Q

If you have reason to believe the compound you want to measure after dry ashing may be reacting with porcelain crucibles being used, what can you do to fix this?

A

Use a different material for the crucible (e.g., platinum)

202
Q

What do you do if you want to determine the iron content of food but cannot seem to get the iron solubilized after dry ashing?

A

Use a wet-ashing procedure instead

203
Q

What are some important considerations when selecting solvents to be used in continuous and noncontinuous solvent extraction methods?

A
  • Ideal characteristics
    • High solvent power for lipids
    • Low solvent power for proteins, amino acids, and carbohydrates
    • Evaporate relatively easily and leave no residue
    • Have a relatively low boiling point
    • Be nonflammable and nontoxic in both liquid and vapour states
    • Penetrate sample particles readily
    • Be in single component form to avoid fractionation
    • Be inexpensive
    • Be nonhygroscopic
204
Q

Itemize the procedures that may be required to prepare a food sample for accurate fat determination by a solvent extraction process. Explain why each procedure is necessary. [3]

A

Pre-drying sample → fats cannot be efficiently extracted from moist foods with ethyl ether; ether saturated with water is inefficient for fat extraction; dried samples are easier to grind; breaks fat-water emulsions to make fat easier to extract

Particle size reduction → increases the efficiency of extraction

Acid hydrolysis (or alkaline hydrolysis) → breaks covalently and ionically bound lipids (i.e., bound to proteins and carbs) so lipid is extractable

205
Q

You performed fat analysis on a new superenergy shake (high carbohydrate and protein) using standard Soxhlet extraction. The value obtained for fat content was much lower than that expected.

What could have caused the measured fat content to be low, and how would you modify the standard procedure to correct the problem?

A

The proteins and carbohydrates in the shake interact with the fat (causing it to be bound tightly), which makes it difficult to extract. Results may be lower. Modify the procedure by alkaline or acid hydrolysis prior to fat extraction.

206
Q

Describe the purpose of the chemicals used in the Mojonnier method:

Ammonium hydroxide

Ethanol

Ethyl ether

Petroleum ether

A

Ammonium hydroxide → neutralizes the acidic sample and causes proteins to precipitate

Ethanol → prevents possible gel formation

Ethyl ether → dissolves lipid

Petroleum ether → removes moisture from the ethyl extract and dissolves more nonpolar lipids

207
Q

What is the key application of the gas chromatography fat extraction method and what does it specifically quantify?

A

Nutrition labelling

Quantifies each individual fatty acid (sum is total fat content)

208
Q

What is the purpose of sulfuric acid addition in the Babcock method?

A

Digest protein, generate heat (heat helps maintain fat in a liquid state to help with fat release and extraction), release the fat

209
Q

What is the purpose of centrifugation and addition of hot water in the Babcock method?

A

Separate fat from the rest of the sample and brings it to the graduated portion of the test bottle so it can be quantified volumetrically

210
Q

Babcock uses gravimetric determination of lipid content.

True or False?

A

False.

Babcock uses volumetric determination of lipid content.

211
Q

Gerber uses volumetric determination of lipid content.

True or False?

A

True.

212
Q

Gerber uses gravimetric determination of lipid content.

True or False?

A

False.
Gerber uses volumetric determination of lipid content.

213
Q

Babcock uses volumetric determination of lipid content.

True or false?

A

True.

214
Q

Soxhlet uses gravimetric determination of lipid content.

True or False?

A

True.

215
Q

Soxhlet uses volumetric determination of lipid content.

True or False?

A

False.

Soxhlet uses gravimetric determination of lipid content.

216
Q

Mojonnier uses gravimetric determination of lipid content.

True or False?

A

True

217
Q

Mojonnier uses volumetric determination of lipid content.

True or False?

A

False.

Mojonnier uses gravimetric determination of lipid content.

218
Q

Describe an ideal solvent for fat extraction. [8]

A

Ideal solvents for fat extraction have:

  • A high solvent power for lipids
  • Low or no solvent power for proteins, amino acids, and carbohydrates.
  • Ability to evaporate readily and leave no residue.
  • A relatively low boiling point
  • Nonflammable in both liquid and vapour states.
  • Nontoxic in both liquid and vapour states.
  • Single component form to avoid fractionation
  • Inexpensive.
  • Nonhygroscopic
219
Q

What are some important considerations when selecting solvents to be used in continuous and noncontinuous solvent extraction methods?

A
  • Continuous methods
    • Fire risk
    • Channeling
    • Too dangerous to use ethyl ether → petroleum ether.
  • Semicontinuous
    • Soaking effect → no channeling
    • Too dangerous to use ethyl ether → petroleum ether.

Ideal solvents for fat extraction have: (hard to find solvents to meet all of these characteristics)

  • A high solvent power for lipids
  • Low or no solvent power for proteins, amino acids, and carbohydrates.
  • Ability to evaporate readily and leave no residue.
  • A relatively low boiling point
  • Nonflammable in both liquid and vapour states.
  • Nontoxic in both liquid and vapour states.
  • Single component form to avoid fractionation
  • Inexpensive.
  • Nonhygroscopic
220
Q

Compare ethyl ether [6] and petroleum ether. [8]

A
  • Ethyl ether
    • BP 34.6 degrees Celsius
    • Better solvent for fat than petroleum ether.
    • Expensive
    • Danger of explosion and fire hazards.
    • Hygroscopic
    • Forms peroxides
  • Petroleum ether
    • Low boiling point fraction of petroleum
    • Composed mainly of pentane and hexane
    • BP 35-38 degrees Celsius
    • More hydrophobic than ethyl ether
    • Selective for more hydrophobic lipids
    • Cheaper
    • Less hygroscopic than ethyl ether
    • Less flammable than ethyl ether
221
Q

To extract the fat from a food sample, you have the choice of using ethyl ether or petroleum ether as the solvent, and you can use either a Soxhlet or a Goldfish apparatus. What combination of solvent and extraction would you choose? Give all the reasons for your choice.

A

I would use petroleum ether as it is less flammable and less toxic than ethyl ether, and I would use Soxhlet because it is the official method, and there is no channeling issues. Further, Goldfish has a significant fire hazard risk associated with its procedure.

222
Q

You performed fat analysis on a new super energy shake (high carbohydrate and protein) using standard Soxhlet extraction. The value obtained for fat content was much lower than that expected. What could have caused the measured fat content to be low, and how would you modify the standard procedure to correct the problem?

A

The proteins and carbs in the shake interact with the fat (causing it to be bound tightly), which makes it difficult to extract. Results may be lower than expected. Modify the procedure by adding an acid digestion prior to standard fat extraction.

223
Q

What is the purpose of the following chemicals used in the Mojonnier method?

(a) Ammonium hydroxide
(b) Ethanol
(c) Ethyl ether
(d) Petroleum ether

A

(a) Ammonium hydroxide → Neutralizes the acidic sample and dissolves protein

(b) Ethanol → Prevents possible gel formation

(c) Ethyl ether → Dissolves the lipid

(d) Petroleum ether → Removes moisture from the ethyl ether extract and dissolves more nonpolar lipids

224
Q

What is a key application of the GC method and what does it specifically quantify?

A
  • The key application of the GC method is that it is the most common method used for nutrition labeling.
  • Quantifies each individual fatty acid which gives the total fat
    • Total fat = sum of fatty acids from C4 to C24 calculated as triglycerides, is “total fat” (including weight of glycerol per 3 FA)
225
Q

What is the purpose of the following procedures used in Babcock method?

(a) Sulfuric acid addition
(b) Centrifugation and addition of hot water

A

(a) Digest protein, generate heat, and release the fat.
(b) Separates fat from the rest of the sample and brings it to the graduated portion of the test tube so it can be quantified.

226
Q

What factors should one consider when choosing a method for protein determination?

A
  1. principle/basis of the method
  2. purpose of analysis
  3. sensitivity; detection limit
  4. speed, equipment, and technical expertise
227
Q

The Kjeldahl method of protein analysis consists of three major steps. List these steps in the order they are done and describe in words what occurs in each step. Make it clear why milliliters of HCl can be used as an indirect measure of the protein content of a sample.

A

1) DIGESTION → Digest protein with H2SO4 in presence of catalyst → Food + Sulfuric Acid → gives Nitrogen in the form of Ammonium sulfate (NH4)2SO4
2) NEUTRALIZATION/DISTILLATION → Neutralize Ammonium sulfate with Sodium Hydroxide (NaOH) → produce ammonia (NH3), distill the NH3 into Boric acid to produce NH4 and Borate ions
3) TITRATION → Titrate Borate ion with dilute HCl to colorimetric endpoint. Volume of HCl needed is indicative of protein content.

HCl can be used as indirect measure because that’s the titrant used to titrate the borate ion. The quantity of borate ion (generated over the procedure) is indicative of the amount of nitrogen (and thus protein) present.

Volume of HCl → moles of borate anions → moles NH3 → moles (NH4)2SO4 → moles N → protein content

228
Q

Why is the conversion factor from Kjeldahl nitrogen to protein different for various foods, and how is the factor of 6.25 obtained?

A

Average MW of N relative to MW of an amino acid is 16%. 100/16 = 6.25

Not all amino acids have the same N content, so foods of different amino acid composition will have different conversion factors. Different conversion factors are needed because the protein composition/amino acid composition differs (some a.a. have more N than others) and thus some proteins have more/less N.

229
Q

Differentiate the principles of protein determination by dye binding with an anionic dye such as Amido Black vs. the Bradford method, which uses the dye Coomassie Blue G-250.

A

Bradford → uses binding of Blue G-250 dye to proteins which results in a dye protein complex (driven by electrostatic & non-polar interactions, particularly to Arginine + aromatic residues); read absorbance at 595nm; relies on amphoteric nature of proteins; the change in the absorbance at 595nm is proportional to the protein concentration of the sample; the dye changes colour from reddish to bluish; measure A595, calculate [protein] using a standard curve.

Anionic dye binding → basic amino acid residues (like His, Arg, Lys) in protein (and the free amino terminal group) react with the anionic sulfonic acid dye and form an insoluble complex (= precipitate out of solution); the unbound soluble dye is measured by absorbance → amount is inversely related to the protein content of the sample → [dye]total = [dye]super + [dye]protein-bound

230
Q

With the anionic dye-binding method, would a sample with a higher protein content have a higher or a lower absorbance reading than a sample with a low protein content? Explain your answer.

A

In the anionic dye-binding method, the amount of unbound dye is inversely related to the protein content of the sample. Therefore, a lower absorbance would be associated with a higher protein content, since protein is available to bind the dye. A lower protein content would have a higher absorbance, which is why there is so much unbound dye remaining.

In other words, higher protein content sample has lower absorbance reading because more of the excess dye has reacted with the protein, leaving less dye left in solution.

231
Q

For each of the situations described below, identify a protein assay method most appropriate for use and indicate the chemical basis of the method (i.e., what does it really measure?)

(b) Intact protein eluting from a chromatography column; qualitative or semiquantitative method

A

Method: Absorbance at 280nm

Chemical basis: Presence of tyrosine and tryptophan; absorbance is related to concentration by Beer’s Law.

232
Q

The FDA found melamine (see structure below) in pet food linked to deaths of pets in the United States. The FDA also found evidence of melamine in wheat gluten imported from China used as one of the ingredients in the production of the pet food. Melamine is a nitrogen-rich chemical used to make plastic and sometimes used as a fertilizer.

(a) Knowing that each ingredient is tested and analyzed when imported, explain how melamine in wheat gluten could have escaped detection.

(b) How can the adulteration of wheat gluten be detected (not necessarily detecting melamine specifically) using a combination of protein analysis methods. Explain your answer.

A

(a) Dumas method detects nitrogen. Since melamine contains nitrogen Dumas would detect the nitrogen from melamine and protein without differentiating. They weren’t measuring melamine, they were measuring nitrogen. Melamine has many nitrogen molecules, which are measured in the Kjeldahl or Dumas methods, and are calculated as protein. These methods cannot distinguish between protein N and non-protein N.
(b) Using a combination of methods based on different principles would give different answers if melamine was present, e.g., Dumas method based on nitrogen content, and infrared based on peptide bonds. Or use TCA to precipitate out the proteins (i.e., remove by filtering, centrifuging) then determine non-protein nitrogen using Kjeldahl or Dumas. There should not typically be substantial amounts of non-protein nitrogen in a food sample.

233
Q

For each of the situations described below, identify a protein assay method most appropriate for use and indicate the chemical basis of the method (i.e., what does it really measure?)

(a) Nutrition labeling

A

Method: Dumas or Kjeldahl

Chemical basis Dumas: Total N, converted to % protein; N is released upon combustion, and measured by gas chromatography using thermal conductivity detector

Chemical basis Kjeldahl: Total N, converted to % protein; determine N by method involving digestion, neutralization, distillation, and titration

234
Q

For each of the situations described below, identify a protein assay method most appropriate for use and indicate the chemical basis of the method (i.e., what does it really measure?)

(c) Intact protein eluting from a chromatography column; colorimetric, quantitative method

A

Method: BCA method (or Lowry or dye binding)

Chemical basis BCA: proteins reduce cupric ions to cuprous ions under alkaline conditions; cuprous ions react with BCA reagent to give purple colour

235
Q

For each of the situations described below, identify a protein assay method most appropriate for use and indicate the chemical basis of the method (i.e., what does it really measure?)

(d) Rapid, quality control method for protein content of cereal grains

A

Method: NIR

Chemical basis: Presence of peptide bond in protein molecule causes absorption of radiation at specific wavelengths in mid- or near-infrared region

236
Q

Describe the importance of carbohydrates in nutrition labelling [3] and functional properties [7].

A
  • Nutrition labelling → source of energy, sugars & fibre
  • Functional properties → sweetness, texture, viscosity, water-binding capacity, lowering aw , freezing point suppression, chemical reactivity (colour, flavour, aroma, reducing sugars)
237
Q

What are digestible CHO?

A
  • simple sugars
    • monosaccharides e.g., D-glucose, D-fructose
    • disaccharides e.g., sucrose, lactose, maltose
  • Maltodextrins (oligosaccharides)
  • Starch (polysaccharides)
238
Q

What are indigestible CHO?

A
  • Dietary fiber (indigestible CHO + lignin)
    • Soluble (pectin, gums, hydrocolloids)
    • Insoluble (cellulose, hemicellulose, resistant starch, & lignin)
239
Q

What are sugar alcohols?

A

Sorbitol

Xylitol

Maltitol

Sugar alcohols are organic compounds, typically derived from sugars, containing one hydroxyl group attached to each carbon atom. They are white, water-soluble solids that can occur naturally or be produced industrially by hydrogenation of sugars. Since they contain multiple –OH groups, they are classified as polyols. Wikipedia

240
Q

Monosaccharides are the building blocks of CHO.

How are they classified?

A

Degree of Polymerization (DP)

Sugars, DP = 1-2

Oligosaccharides, DP = 3-9

Polysaccharides, DP > 9

241
Q

Give examples of food with CHO content that is mostly starch.

A

Cereals, bread, pasta

242
Q

Give examples of food with CHO content that is mostly sugars.

A

Dairy products

243
Q

Give examples of food with starch, sugars and fibre CHO content.

A

Fruits and veg

244
Q

Give examples of food where the CHO content is added.

A

Meat, poultry, fish, beer.

245
Q

Summarize the methods of CHO analysis. [4]

A
  • Total CHO
    • Calculated by difference
    • Phenol sulfuric acid method
  • Mono & oligosaccharides
    • Total reducing sugar analysis e.g., Somogyi-Nelson & Lane-Eynon methods
    • Analysis of specific mono-, di-, and oligosaccharides by HPLC, GC, or enzymatic methods
  • Polysaccharides
    • Starch
    • Fibre (total, insoluble & soluble)
  • Physical methods
    • Specific gravity
    • Refractive index
246
Q

Describe CHO sample preparation. [5]

A
  • Dry the sample
  • Grind to fine powder → increases surface area
  • Extract lipids (e.g., with chloroform-methanol or hexane etc…, in Soxhlet extractor) → makes carbohydrate extraction easier and more complete
  • Extract with hot 80% ethanol
    • monosaccharides and oligosaccharides are soluble
    • polysaccharides and proteins are insoluble
    • if acidic, include calcium carbonate to neutralize acidity → to prevent sucrose hydrolysis
  • 80% ethanol extract obtained
    • Remove charged contaminants with ion-exchange technique
    • Use rotary evaporator to remove aqueous alcohol
247
Q

What is the definition given by FDA for nutrition labelling for %CHOtotal?

A

%CHOTOTAL = 100 - %(moisture + ash + fat + protein)

  • Calculated by difference from proximate analysis
  • Always calculated (i.e., not actually measured)
  • Measure contents of moisture, ash, lipid, and protein, then calculate ‘total carbohydrate’.
248
Q

Describe the principle of the phenol-sulfuric acid method.

A
  • Digest (acid hydrolysis) CHO → monosaccharides
  • Heating + H2SO4 converts monosaccharides into various degradation products (furans) that react with phenol → coloured reaction products (orange, yellow)
  • Measure absorbance at 490nm
  • Relate increase in A490nm with [CHO]total using a standard curve
249
Q

Describe the limitations of the phenol-sulfuric acid method. [3]

A
  • Virtually all CHO react, but to different extents
  • Accuracy depends on use of appropriate standard (i.e., as similar to sample as possible)
    • If CHO composition is unknown = use D-glucose
  • Dose not detect sugar alcohols (e.g., sorbitol, maltitol)
250
Q

Describe the principle of using reducing sugars [1] to determine CHO content. [3]

A
  • Reducing sugar → any CHO with the hemiacetal group; the free aldehyde (non-cyclic form) of aldoses is available for redox reactions
  • Reduction of Cu (II) → Cu (I) by reducing sugars under alkaline conditions
  • Determination of Cu (I) by VIS absorption or titration
  • Relate absorbance or volume titrant to [reducing sugar] using a standard curve
251
Q

How do Somogyi-Nelson and Lane-Eynon methods differ in how Cu (I) is determined?

A
  • Somogyi-Nelson method (measure absorbance at 520 nm)
    • Reaction of Cu (I) with arsenomolybdate → blue pigment
  • Lane-Eynon method
    • Titration of Cu (II) solution (of known concentration) with sample
    • Measure volume of sample required to titrate all Cu (II) → Cu (I)
      • Solution turns from blue to clear
252
Q

Describe limitations of reducing sugars in CHO analysis. [2]

A
  • Each reducing sugar reacts slightly differently
  • Accuracy depends on use of appropriate standard (e.g., D-glucose or mixture)
253
Q

Briefly list how mono- & oligosaccharides can be analysed. [2]

A
  • Analysis of specific mono-, di-, and oligosaccharides by HPLC, GC, or enzyme methods
  • Analysis of total reducing sugars
    • Reduction of Cu2+ → Cu+
    • Somogyi-Nelson & Lane-Eynon methods
254
Q

What is the principle of chromatography methods in CHO analysis?

A

Separate and quantify compounds based on area under the peak.

255
Q

Describe HPLC in CHO analysis.

A

High Performance Liquid Chromatography

  • Extract samples & filter
  • Separate mono- & oligos- based on
    • Charge (anion exchange) → at high pH (pKa ~12-14)
    • Polarity (normal phase HPLC)
256
Q

Describe GC in CHO analysis. [2]

A

Samples must be (1) converted to sugar alcohols and (2) esterified to make them volatile = extensive sample prep!

Note on esterification: Fermentable. Hydrophilic, may cause osmotic stress in the GI tract. There is evidence xylitol can be digested. Reduce sugars like D-Galactose to form the sugar alcohol, then esterify / acetylate to make it more volatile. Note the planar ketone of D-fructose gives rise to a mixture of two alditols depending on which way the attack happens.

257
Q

Describe the principle of enzymatic methods in CHO analysis.

A

Enzyme uses sample as substrate → measure change in Absorbance or change in conductivity

258
Q

Describe the isolation and analysis of polysaccharides.

A
  • Insoluble residue (proteins, polysaccharides) → from alcohol extraction of fat-free sample
    • Resuspended in protease buffer
    • Proteins digested with protease
    • Add 80% ethanol
  • Polysaccharide precipitate
    • Suspend in amylase buffer
    • Remove (or analyse) starch by digestion
    • Centrifuge
  • Residue = insoluble fiber
  • Soluble = soluble fibre, starch hydrolysis products
    • Further separation, acid hydrolysis and analysis by HPLC, GC e.g., hydrocolloids, gums
259
Q

Describe the principle of starch analysis. Describe the method.

A
  • Principle:
    • Digest (enzymes) starch into D-glucose
    • Measure [D-glucose]
  • Starch
    • Gelatinize in hot DMSO → hot DMSO minimizes formation of resistant starch
  • Starch solution
    • Digest with alpha-amylase
  • Linear and branched fragments of amylose and amylopectin
    • Digest with glucoamylase
  • D-glucose
    • GOPOD reagent
  • Colour
    • Proportional to amount of D-glucose released
260
Q

What is dietary fibre?

A
  • Dietary fibre ~ sum of the nondigestible components
  • Plant-derived or not (e.g., synthetic, microbial, algal)
  • Includes: polysacchardies (all but starch), and oligosaccharides (all but sucrose, lactose & maltose)
261
Q

Give examples of insoluble dietary fibre and soluble dietary fibre.

A
  • Insoluble
    • Cellulose
    • Lignin
    • Insoluble hemicelluloses (and soluble hemicelluloses entrapped in the lignocellulosic matrix)
    • Resistant starch
  • Soluble
    • Soluble hemicelluloses (not entrapped)
    • Pectin (most)
    • Hydrocolloids (most)
    • Non-digestible oligosaccharides
262
Q

Describe TDF gravimetric analysis.

A
  • Defat sample if >10% lipid
    • (a) Treat mixture with an alkaline protease → digest protein
    • (b) Treat hot mixture with a thermostable alpha-amylase → digest starch
    • ( c) Treat mixture with glucoamylase → digest starch
    • (d) Add 4 volumes 95% ethanol
      • Collect residue & precipitate by filtration. Wash with 78% ethanol, 95% ethanol, and acetone. Air dry; then oven dry. Weigh. (residue = total dietary fibre)
      • Subtract weights of protein and ash determined on duplicate samples → perform Kjeldahl & muffle furnace methods on identical/separate samples = correct for trapped protein & ash
263
Q

Describe IDF gravimetric analysis.

A
  • Defat sample if >10% lipid
    • (a) treat mixture with an alkaline protease → digest protein
    • (b) treat hot mixture with a thermostable alpha-amylase → digest starch
    • ( c) treat mixture with glucoamylase
      • Filter (obtain residue)
      • Wash with water to remove anything soluble
      • Wash with 78% EtOH, 95% EtOH, and acetone.
      • Dry and weigh = insoluble fibre
      • Soluble fibre = in the filtrate.
264
Q

Describe SDF gravimetric analysis.

A
  • After digesting protein & starch from defatted sample
    • Filter (obtain residue) & wash with water (obtain filtrate)
    • Precipitate soluble fibre with 78% EtOH
    • Filter (obtain residue) & wash with 78% EtOH, 95% EtOH, acetone.
    • Dry and weigh = soluble fibre
265
Q

Describe CHO analysis by specific gravity.

A
  • From Archimedes’ principle → to float, the standard mass must be displaced by an equal mass of liquid
  • Standard mass = mass of liquid displaced
  • Volume displaced = read from scale on hydrometer
  • Insert into sample of interest, read depth off of scale (e.g., calibrated to specific gravity OR calibrated in Brix (1 Brix = 1 g sucrose/100g sample))
266
Q

Describe CHO analysis by refraction.

A
  • Based on bending of light (i.e., refraction) as it hits surface of product
  • By holding temperature and wavelength of light constant, use RI to determine [compound of interest]
267
Q

Describe the importance of minerals in food. [6]

A
  • Nutrition labelling → Na, Ca, Fe, K
  • Food Fortification → Ca, Fe, Zn, I
  • Food Processing → Na, P, Ca
  • Water hardness → Ca, Mg
  • Water Quality → Pb
  • Toxicity → F, Se, heavy metals
268
Q

Summarize the methods for mineral analysis and when to use them.

A

AAS = atomic absorption spectroscopy

ICP-OES = inductively coupled plasma-optical emission spectroscopy

269
Q

Describe how contamination is avoided in mineral analysis.

A
  • From cutting, grinding (e.g., use aluminum blades)
  • Use clean glassware (clean with acid rinse)
  • Use pure water (e.g., distilled, deionized, filtered) and reagents
  • Run a reagent blank - use to subtract out contaminants
270
Q

Describe background interferences/matrix effects in mineral analysis.

A

Matching → prepare standards in solution with other key components known to be in the sample

*

270
Q

Describe how background interferences/matrix effects in mineral analysis are mitigated.

A

Matching → prepare standards in solution with other key components known to be in the sample

  • Match the background matrix solutions
  • Contains elements known to exist in the sample at the same level they exist in the sample
  • Matched solution used to make standard curve for element of interest
  • Purpose is to overcome problems related to interferences

Spiking → ‘spike’ the sample with a standard (small volume, concentrated)

  • Add spikes to the sample at the start of the procedure to account for incomplete extraction and mineral degradation.
  • Compare the spiked and non-spiked samples (difference should = amount of spike added)
  • Purpose is to test for matrix effects (i.e., if get less analyte out than put in)
271
Q

What is matching in mineral analysis used for?

A

Matching → prepare standards in solution with other key components known to be in the sample

  • Match the background matrix solutions
  • Contains elements known to exist in the sample at the same level they exist in the sample
  • Matched solution used to make standard curve for element of interest
  • Purpose is to overcome problems related to interferences
272
Q

What is spiking in mineral analysis used for?

A

Spiking → ‘spike’ the sample with a standard (small volume, concentrated)

  • Add spikes to the sample at the start of the procedure to account for incomplete extraction and mineral degradation.
  • Compare the spiked and non-spiked samples (difference should = amount of spike added)
  • Purpose is to test for matrix effects (i.e., if get less analyte out than put in)
273
Q

Mineral analysis may require pre-ashing.

True or False?

A

True. Often wet-ashing.

Especially colorimetric methods, instrumental methods.

Separation of minerals from food components.

274
Q

Briefly summarize methods for mineral analysis.

A
  • Titration
    • EDTA complexation e.g., measure Calcium, Magnesium
    • Precipitation titration e.g., measure Chloride
      • Forward titration (Mohr)
      • Backward titration (Volhard)
  • Colorimetric
    • Measure many different minerals
  • Ion selective electrodes
    • Measure Na+, Ca2+, H+
275
Q

What is the principle of EDTA complexation titration?

A
  • Ions initially bound to metal ion indicator
  • EDTA has greater affinity for the ions
  • Titrate with EDTA until all ions are freed from indicator
  • Indicator turns blue = end point
  • Moles EDTA = moles analyte (Ca2+, Mg2+)
276
Q

What are limitations of the EDTA complexation titration method of mineral analysis?

A
  • Titration must occur at pH ~10-11
    • EDTA affinity for ions reduces at pH < 10
    • Mg and Ca precipitate near pH 12
277
Q

What are applications of the EDTA complexation titration method of mineral analysis?

A
  • Water hardness (Ca2+, Mg2+)
  • Ca2+ in fruits and vegetables
278
Q

Describe the principle of forward/direct (Mohr) precipitation titration.

A
  • Cl- is titrated with Ag+ (f. silver nitrate, AgNO3)
  • Excess Ag+ reacts with chromate indicator to form orange precipitate = endpoint
  • Amount of silver nitrate used relates to amount of NaCl present in sample
279
Q

What is a limitation of the forward/direct (Mohr) precipitation titration method of mineral analysis?

A

Over-titration (→) results in over-estimation of NaCl content

280
Q

What is an application of the forward/direct (Mohr) precipitation titration method of mineral analysis?

A

NaCl content in food

(Assumes all Cl- from NaCl)

281
Q

What is the principle of backward/indirect (Volhard) precipitation titration method of mineral analysis?

A
  • Excess silver nitrate is added to react with all Cl-
  • Back titrate excess Ag+ with potassium thiocyanate
  • Ferric ion indicator + excess SCN → red = endpoint
  • Relate amount of thiocyanate to excess Ag, to calculate amount of Ag+ that reacted with Cl-
282
Q

What is a limitation of backward/indirect (Volhard) precipitation titration method of mineral analysis?

A

Over-titration (→) results in under-estimation of NaCl content

283
Q

What is an application of backward/indirect (Volhard) precipitation titration method of mineral analysis?

A

NaCl content of food

284
Q

Over-titration using the Volhard method of mineral analysis results in over-estimation of NaCl content.

True or False?

A

False.

Over-titration using the Volhard method of mineral analysis results in under-estimation of NaCl content.

285
Q

Over-titration using the Volhard method of mineral analysis results in under-estimation of NaCl content.

True or False?

A

True.

286
Q

Over-titration using the Mohr method of mineral analysis results in over-estimation of NaCl content.

True or False?

A

True.

287
Q

Over-titration using the Mohr method of mineral analysis results in under-estimation of NaCl content.

True or False?

A

False.

Over-titration using the Mohr method of mineral analysis results in over-estimation of NaCl content.

288
Q

What is the principle of the EDTA titration method of mineral analysis?

A

Description for sample containing just calcium:

EDTA of titrant solution complexes with calcium 1:1; EDTA binds to calcium ions stronger than the indicator binds to calcium. When all the calcium present in the sample has reacted the EDTA titrant, and no calcium is bound to the indicator, the indicator changes from pink to blue.

Moles of calcium in the sample are equivalent to moles of EDTA used in titration.

289
Q

What are applications of the EDTA titration method of mineral analysis?

A

Testing water hardness.

Calcium in ash of fruits and vegetables.

290
Q

What are advantages and disadvantages of the EDTA titration method of mineral analysis?

A
  • Advantages → rapid, especially when done with test strip; inexpensive
  • Disadvantages → Can be interfering compounds. endpoint is subjectively determined.
291
Q

What is the principle of Mohr titration?

A

A forward titration.

Chloride (in NaCl) is titrated with silver nitrate in the presence of potassium chromate. Silver reacts with the chloride; when all chloride is reacted, the excess silver reacts with chromate to form an orange-coloured solid, silver chromate.

Volume and molarity of silver nitrate are used to calculate amount of chloride, which relates to amount of NaCl.

292
Q

What is the principle of Volhard titration?

A

A backward titration.

An excess of a standard solution of silver nitrate is added to a chloride-containing solution. Excess silver nitrates is back-titrated with a standardized solution of potassium or ammonium thiocyanate, with ferric ion as an indicator.

Volume of thiocyanate solution used is proportional to the excess silver. Moles of total silver is equal to the sum of the moles of chloride in the sample and moles of thiocyanate in the titrant.

293
Q

Describe the principle of colorimetric methods of mineral analysis.

A

Description for just mineral analysis: Chromogen in reagent reacts with mineral of interest to form a soluble coloured compound that can be quantitated by absorption of light at a specific wavelength.

Concentration of mineral of interest is determined from standard curve of absorbance vs. concentration, based on Beer’s Law.

294
Q

What are advantages and disadvantages of Mohr titration?

A
  • Advantages → does not require expensive equipment, highly trained personnel, or ashing of sample; fewer reagents and less time-consuming than Volhard titration; inexpensive (unless automated equipment)
  • Disadvantages → Subjectivity of determining endpoint of titration (if manual titration)
295
Q

What are advantages and disadvantages of Volhard titration?

A
  • Advantages → Does not require expensive equipment, highly trained personnel, or ashing of sample; rapid; inexpensive
  • Disadvantages → Subjectivity of determining endpoint of titration. Requires more reagents and time than Mohr titration.
296
Q

What are advantages and disadvantages of colorimetric methods of mineral analysis?

A
  • Advantages → applicable to wide variety of minerals; very specific; other minerals usually don’t interfere; less expensive than AAS or ICP-OES, but similar accuracy and precision
  • Disadvantage → requires significant technician time.
297
Q

What is the principle of ion-selective electrodes?

A

Principle is the same as for measuring pH (i.e., uses Nernst equation), but by varying the composition of the glass in the sensing electrode, the electrode can be sensitive to a specific mineral.

Sensing and reference electrodes (often as combination electrode) are immersed in solution with element of interest; electrical potential that develops at surface of sensing electrode is measured by comparing to reference electrode with fixed potential.

Voltage between sensing and reference electrode is related to ion activity, measured in mV. Ion activity is related to ion concentration via the activity coefficient, which is controlled by ionic strength.

Concentration of element is determined using standard curve of mV vs. log concentration

298
Q

What is an application of Mohr titration?

A

Salt content of a variety of foods.

Test strip version and automated instruments available.

299
Q

What is an application of Mohr titration?

A

Salt content of a variety of foods.

Test strip version and automated instruments available.

300
Q

What is an application of Volhard titration?

A

Salt content of a variety of foods.

301
Q

What is an application of colorimetric methods of mineral analysis?

A

Low-cost method for analyzing single element.

302
Q

What are advantages and disadvantages of ion-selective electrodes in mineral analysis?

A
  • Advantages → can measure anions and cations directly; does not require expensive equipment (only pH meter), highly trained personnel, or ashing of sample; analysis is independent of turbidity, colour, or viscosity.
  • Disadvantages → cannot measure at low concentration; electrode response can be slow; sensing and reference electrode must be specific to element being measured; high rate of premature failure for some electrodes.
303
Q

What is the principle of colorimetric mineral analysis?

A
  • A chromogen reacts with a mineral to form a coloured compound
  • Measure VIS absorbance
  • Relate absorbance to [analyte] via:
    • Molar extinction + Beer-Lambart law (A = elc)
    • OR, use a standard curve (Abs. vs. Conc.)
304
Q

What is a limitation and application of the colorimetric mineral analysis method?

A
  • Limitation → generally, sample must be pre-ashed to obtain solubilized analyte
  • Application → phosphorus, + a variety of minerals in food
305
Q

What is the principle of ion-selective electrodes (ISE)?

A
  • Electrode selective for a specific ion (e.g., Ca2+, Na+, Cl-, K+, etc…)
  • Measure voltage between sensing and reference electrode
  • Electrical potential (voltage) developed is related to concentration of the ion
  • Use standard curve to relate potential to [ion]
306
Q

What are applications of ISE? [5]

A
  • Na, Cl (salt content)
  • Ca in milk
  • Na, K in wine
  • CO2 in sodas
  • Nitrate in meat and vegetables
307
Q

Discuss using ISE at low concentrations.

A
  • Plot electrode potential (mV) vs. log[ion]
  • Has positive or negative slope depending on element
  • At low concentrations → standard curve is not linear; takes longer to give a stable and reliable reading
308
Q

Discuss the importance of ionic strength and temperature in ISE mineral analysis.

A
  • ISE is responsive to ionic activity
  • Ionic strength should be the same in samples and standards
  • Add ionic strength adjustment (ISA) buffer to all samples and standards.
  • All measurements should be done at the same temperature → 25 degrees C is often the standard
309
Q

Name 5 factors that may interfere with mineral analysis.

A

pH

Sample matrix

Temperature

Analytical conditions

Reagents

310
Q

What is a T-type titration?

A

ISE may be used to detect titration end point (potentiometric titrations)

311
Q

Describe types of ISE.

A
  • Glass membrane → H+, Na+, Ca2+, NO3-
  • Solid state → Cl-, I-, Ag+, Pb2+
  • Gas-sensing → NH3, CO2, O2
  • Immobilized biosensors → glucose oxidase, urease

Note: electrodes are selective, not specific, for the designated ion → possible interferences for each electrode (see examples, ORION ISE specifications)

312
Q

Describe QC methods of mineral analysis.

A

Colorimetric assays implemented for application to test strips

Detect end-point by visual observation of colour

Fast, easy, cheap: QC, field analysis

313
Q

“Proximate composition” refers to analysis for moisture, ash, fat, protein, and carbohydrate.

Identify which of these components of “proximate composition” are actually required on a nutrition label.

Also, explain why it is important to measure the non-required components quantitatively if one is developing a nutrition label.

A
  • Components of ‘proximate composition’ on nutrition label - protein, fat, carbohydrate
  • Quantitate also moisture and ash so total carbohydrate can be calculated as follows:
    • % Total CHO = 100% - (% protein + % ash + % moisture)
314
Q

Distinguish chemically between monosaccharides, oligosaccharides, and polysaccharides, and explain how solubility characteristics can be used in an extraction procedure to separate monosaccharides and oligosaccharides from polysaccharides.

A
  • Monosaccharides, sometimes called ‘simple sugars’, are carbohydrates that cannot be broken down into smaller units by hydrolysis. They are soluble in both water and 80% alcohol.
  • Oligosaccharides are also low MW compounds. They are oligomers of 2-10 monosaccharide units, most often 2-4 units, and yield monosaccharides upon hydrolysis. The monosaccharide units are joined via glycosidic linkages. Most oligosaccharides, like monosaccharides, are soluble in hot 80% ethanol.
  • Polysaccharides are high MW polymers of monosaccharides. Polysaccharides are insoluble in hot 80% ethanol.
    • Both oligo- and poly-saccharides yield monosaccharides upon hydrolysis by hot acid or specific enzymes.
315
Q

Define “reducing sugar”.

Classify each of the following as a reducing or non-reducing carbohydrate: D-glucose, D-fructose, sorbitol, sucrose, lactose, amylose, and cellulose.

A

Reducing sugar → a sugar with a free aldehyde group (non-cyclic) or a hemiacetal group

  • D-glucose → reducing
  • D-fructose → reducing under alkaline conditions (nonreducing under neutral or acidic conditions)
  • Sorbitol → non reducing
  • Sucrose → non reducing
  • Lactose → reducing
  • Amylose → non reducing
  • Cellulose → non reducing

Note: the polysaccharides have a reducing end unit but are nonreducing because of their high MW.

316
Q

Describe the principle behind each step in figure 19.9.

What is the reason for each step?

A

(a) Freeze dry sample and extract fat. Dry sample, without heating, to allow for easy grinding and extracting the fat-soluble substances. The removal of fat-soluble substances with organic solvents (e.g., chloroform-methanol) makes the extraction of polysaccharides more quantitative.
(b) Aqueous ethanol extract. Sugars, other low MW compounds, and ash, can be removed by dissolving them in hot 80% ethanol, so these compounds don’t interfere with the final analysis.

(c ) Protein digestion. Proteins are solubilized in a buffer, heated to denature them, then hydrolyzed with enzymes (papain or bacterial alkaline proteases) to amino acids and small peptides that are not precipitated with ethanol.

(d) Ethanol precipitation. Soluble polysaccharides are recovered by precipitation with ethanol.
(e) Starch digestion, then centrifugation. To remove starch, a polysaccharide that is precipitated with ethanol, it is hydrolyzed with specific enzymes to D-glucose, which will be soluble in 80% ethanol. Centrifugation is used to isolate insoluble polysaccharides.
(f) Precipitation. Polysaccharides that are soluble are precipitated by adding sodium chloride then 4 volumes of ethanol.
(g) Dialysis. The precipitated polysaccharides are dissolved in water. The solution is dialyzed first against water that contains the sodium aside (to prevent microbial growth), then against water alone to remove the sodium azide. The solution is then freeze dried for further analysis.
(h) Hydrolysis. The polysaccharides are hydrolyzed with acid to constituent monosaccharides, so individual sugars present can be determined by HPLC or GC. This is a useful tool for indicating what polysaccharides are present.

317
Q

What is the major concern in sample preparation for specific mineral analysis?

How can this concern be addressed?

A

Contamination → use the purest water and reagents possible → also use a reagent blank

318
Q

If the ammonia buffer is pH 11.5 rather than pH 10 in the EDTA complexometric titration to determine the hardness of water, would you expect to overestimate or underestimate the hardness?

Explain your answer.

A

Hardness of water would be underestimated at pH 11.5 because magnesium and calcium in the water could be precipitated as their hydroxides, so they would not be available to react with the EDTA.

319
Q

In a back-titration procedure, would overshooting the endpoint in the titration cause an over- or underestimation of the compound being quantitated (e.g., Cl-)?

Explain your answer.

A

Overshooting the endpoint in a back titration would cause an underestimation of the compound being quantitated. The excess titrate would indicate there was more free Ag+, which would indicate that less Ag+ was reacted with Cl- and therefore, that there was less Cl- (NaCl) present.

320
Q

Explain the theory of potentiometry and the Nernst equation as they relate to being able to use a pH meter to measure H+ concentration.

A
  1. Potentiometry involves the use of an electrolytic cell composed of two electrodes dipped into a test solution.
  2. A voltage develops, which is related to the ionic concentration of the solution.
  3. Hydrogen ion concentration (activity) is determined by the voltage that develops between the two electrodes.
  4. The Nernst equation relates the electrode response to the activity.
  5. Voltage produced by the electrode system is a linear function of the pH. The electrode potential is +59mV for each change of one pH unit.
321
Q

You return from a 2-week vacation and ask your lab technician about the pH of the apple juice sample you gave him or her before you left. Having forgotten to do it before, the technician calibrates a pH meter with one standard buffer stored next to the meter and then reads the pH of the sample of unpasteurized apple juice immediately after removing it from the refrigerator (40°F), where it has been stored for 2 weeks.

Explain the reasons why this stated procedure could lead to inaccurate or misleading pH values.

A
  • Sample stored for 2 weeks → fermentation would occur, so reduced pH (microbes produce acid)
  • Should have used 2 or 3 standard buffers; using only 1 buffer assumes temperature is related to slope
  • Should do standards at the same temperature as the sample.
322
Q

For each of the food products listed below, what acid should be used to express the titratable acidity?

(a) Orange juice -
(b) Yogurt -
(c) Apple juice -
(d) Grape juice -

A

(a) Orange juice - citric
(b) Yogurt - lactic
(c) Apple juice - malic
(d) Grape juice - tartaric

323
Q

How would you recommend determining the endpoint in the titration of tomato juice to determine the titratable acidity? Why?

A

Colourimetric methods not appropriate due to the dark colour of tomato juice.

  • Use potentiometric method & titrate to certain pH → use the mid-point of the abrupt change in pH as the equivalence point
324
Q

The titratable acidity was determined by titration to a phenolphthalein endpoint for a boiled and unboiled clear carbonated beverage.

Which sample would you expect to have a higher calculated titratable acidity? Why?

Would you expect one of the samples to have a fading endpoint? Why?

A

Unboiled carbonated beverage (which would contain carbon dioxide) would have a higher calculated titratable acidity. The NaOH used for titration reacts with carbon dioxide to produce sodium carbonate and sodium bicarbonate, which reduces alkalinity and sets up a buffer system. Also, the bicarbonate breaks down to generate hydrogen ions that will reduce the pH.

Unboiled carbonated beverage would have a fading endpoint, because carbon dioxide would continue to react with the NaOH and create more buffer, and hydrogen ion generation continues.

325
Q

Describe the importance of pH, acids, and buffers in food.

A
  • pH has a strong effect on:
    • Flavour
    • Colour
    • Texture
    • Stability
    • Nutritional quality
    • Food quality
    • Food safety
326
Q

When is a solution neutral, acidic, or basic?

A
327
Q

What is the ionization constant for water?

A

10-14

328
Q

What is the equation to calculate pH?

A

pH = -log[H+]

or

pH = -log[H3O+]

329
Q

The further the equilibrium lies to the right, the larger the dissociation constant and the smaller the pKa.

True or False?

A

True.

330
Q

The further the equilibrium lies to the right, the smaller the dissociation constant and the larger the pKa.

True or False?

A

False.

The further the equilibrium lies to the right, the larger the dissociation constant and the smaller the pKa.

331
Q

What is the Bronsted-Lowry definition of acids and bases?

What is the definition of ‘neutralization’?

A

Acid = a proton donor

Base = a proton acceptor

Neutralization = ‘the reaction of an acid with a base to form a salt’

332
Q

How is acid strength communicated?

A

Acid dissociation constant

The smaller the pKa value, the stronger the acid.

Strong acids have high Ka values.

333
Q

What is the difference between a strong acid and a weak acid?

A

Strong acids dissociate completely.

Weak acids partially dissociate.

334
Q

What is the principle of pH measurement?

A
  • pH meter is a potentiometer
  • Measures voltage (electrical potential) at infinitesimal current
  • Consists of a reference electrode, indicator electrode, and voltmeter
  • [H3O+] is proportional to the change in the electrical potential
335
Q

What is the Nernst equation?

A
336
Q

Describe how electrode potential changes with changing pH.

A
  • Electrode potential decreases with increasing pH
  • Electrode potential increases with increasing [H3O+]
337
Q

Discuss pH measurement in practice. [5]

A
  • read the instructions for your particular electrode!
  • perform 3-point calibration
  • keep sample solution stirring
  • most common = combination electrode
  • most instruments can adjust for temperature
338
Q

When are buffers used?

A
  • Whenever control of pH is desired/required
    • Many assays (e.g., enzyme activity)
    • Extraction of components (maintain stability, solubility, effect electrostatic interactions)
    • Foods contain natural buffering agents (e.g., organic acids; proteins)
339
Q

What is the HH equation?

A

pH = pKa + log[A-] / [HA]

340
Q

What is buffer capacity is affected by [3]

A
  • [buffer]
  • ionic strength (~negligible <0.1M)
  • temperature (TRIS buffers are relatively sensitive)
341
Q

When is a buffer effective?

A

A buffer is effective only around pH = pKa +/- 1

The strongest buffer capacity is at pH = pKa

342
Q

Why is the acid content of foods important? [5]

A
  • Flavour
  • Fruit ripeness (Brix/acid ratio of fruit)
  • Colour (pH effect)
  • Microbial stability (pH effect)
  • Stability (pH effect)
  • Acids tend to decrease with maturity while sugars increase, so the ratio is a good indicator of fruit maturity.
343
Q

What type of acids are found in foods?

A

A variety

Most are carboxylic acids (e.g., acetic, citric, malic, lactic)

Also → phosphoric acid and carbonic acid (from dissolved carbon dioxide)

344
Q

What is the principle of total titratable acidity?

A
  • Titrate the food sample with a strong base (e.g., standardized 0.1 N NaOH
  • As the OH- neutralizes the acid, the pH rises
  • Indicator added (phenolphthalein) changes colour ~pH 8-9 = end point
  • Use moles NaOH to determine amount of acid (reported as % primary acid)
345
Q

What are limitations of total titratable acidity?

A
  • Difficulty seeing colour change
  • Dissolved carbon dioxide interferes by reacting with hydroxide to form carbonate
    • Pre-boil samples to remove
346
Q

How is %TTA calculated?

A

FNH 302 (3 decks)

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