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nutr 3210 > Proximate analysis > Flashcards

Proximate analysis Flashcards

1
Q

what is food analysis and why is it important?

A
  • the development, application and study of analytical methods for characterizing foods and their constituents
  • important for allergies, health consequences, optimal performance, optimal health, safe and nutritious foods and consumer trust
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2
Q

how is food analysis applied in government regulations and quality control?

A

Government regulations: maintain the quality of foods, ensure the food industry makes safe food with high quality, fair competition between companies producing the same product, eliminate economic fraud
Quality control: ensure that food composition doesn’t change (decrease), characterize raw material

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3
Q

Nutrient Density

A

Nutrient-dense foods: lots of value, little calories
empty calorie foods: little value, lots of calories
- need nutrient-dense foods in a nutritious diet

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4
Q

true or false caloric content predicts nutrient content in food

A

false

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5
Q

What is proximate analysis?

A

analytical determination of moisture content, ether extract (fat content), Ash content (mineral content), nitrogen (protein content) and crude fibre

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6
Q

why is determining the water content in feed important?

A
  • water is weight (part of the price of feed)
  • more water weight = higher shipping cost
  • storage conditions: how long food can sit on the shelf and how safe it is on the shelf
  • too much moisture and food will spoil quickly
  • too little moisture and the food will be less palatable
  • moisture dilutes energy and nutrients in food
  • moisture is important for optimum intake and performance of animals
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7
Q

how do you isolate the moisture content in a feed sample

A
  • start with the feed sample (wet weight) and air dry it to get dry matter
  • what you removed is the moisture (water content)
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8
Q

potential sources of error / limitations for determining moisture content

A
  • drying can remove other volatile compounds like SCFAs and some minerals
  • can cause a slight underestimation of drying weight
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9
Q

how can you mathematically determine % moisture

A

% moisture = (wet weight - dry weight) / (wet weight) x 100

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10
Q

how can you determine the % dry matter from a feed sample

A

dry matter = 100% - % moisture

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11
Q

What are the differences between human and agricultural applications of moisture content

A
  • the agricultural industry is more interested in the composition of dry matter (animal feed)
  • human food labelling is based on wet weight
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12
Q

how do you isolate ether extract (fat content) from a feed sample?

A

-treat the dry matter with an organic solvent (ether extraction) to yield the fat content
- the solution is transferred to a new tube and then dried. the solution is the fat and anything not fat would have precipitated out

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13
Q

how can you calculate % crude fat?

A

% crude fat = (weight of ether extract / wet weight of sample) x 100%

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14
Q

Potential source of error / limitations determining crude fat

A
  • other things are soluble in organic solvents such as chlorophyll, resins, waxes in plants
  • could over-estimate crude fat determination
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15
Q

why is it important to measure ASH (mineral) content?

A
  • nutritional labelling
  • quality and taste of food
  • microbiological stability
  • nutritional requirements
  • manufacturer processing
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16
Q

How do you gather Ash content from a feed sample?

A

after the ether extraction of the dry matter, a residue is taken and ignited
- using the same solution from determining fat content, the precipitate will be used to determine mineral content
- when the tube is ignited everything that is organic is burnt off

17
Q

how do you calculate ash (mineral) content?

A

%ASH = (wight of ASH/weight of sample) x 100%

18
Q

potential sources of error / limitations for calculating ASH conctent

A
  • volatile minerals like iron may be lost during the high-temperature burn
  • no information about individual minerals (which is now mandatory) just the total
19
Q

How can you isolate nitrogen (protein content) from a feed sample

A
  • after the dry matter is produced we use it to carry out the Kjeldahl analysis to determine the nitrogen
    2 assumptions are made when carrying out Kjeldahl
    1. all nitrogen in the sample is in protein
    2. all protein contains 16% nitrogen
20
Q

STeps in the Kjeldahl analysis

A
  1. Digestion: a food sample is mixed with sulfuric acid, which converts nitrogen to ammonia
  2. Distillation - separates the ammonia
  3. Titration - quantifies the amount of ammonia
21
Q

how can you calculate the % crude protein

A

% crude protein = (N in sample x 6.25)/wet weight of sample x 100%

22
Q

what equation is used to estimate crude protein

A

nitrogen x 6.25

23
Q

where do we get 6.25 from in the Kjeldahl analysis

A
  • we assume all protein has 16% nitrogen
    100%(total protein) / 16%(nitrogen) = 6.25
    assume 6.25 unless given a different % nitrogen
24
Q

possible sources of error / limitations of the Kjeldahl analysis

A
  1. assumes all protein has 16% nitrogen
    - actual range is 13%-19%
  2. other sources of nitrogen could be present in the sample
    - nitrates, nitrites, urea, nucleic acids etc. would be in the crude protein calculation
    - slightly over-estimates crude protein content
25
Q

How can we isolate crude fibre from a feed sample?

A
  • after the dry matter is collected an ether extraction is taken and boiled in acid
  • a residue is taken then boiled in alkali to yield ASH + crude fibre
  • the ASH + crude fibre sample is ignited and and the 2 are able to be seperated
26
Q

how can you calculate crude fibre content?

A

%crude fibre = ((weight of ASH + crude fibre)-(wt of ASH after ignited) / wet weight of sample x 100%

27
Q

what is crude fibre?

A
  • mainly tells us about the cellulose and lignan content (insoluble fibres)
  • ## we lose dietary fibres in the crude fibre analysis
28
Q

difference between crude and dietary fibre

A

crude: tells us about insoluble fibres
dietary: describes all fibre both soluble and insoluble

29
Q

Potential sources of error/limitations when calculating crude fibre

A
  1. unable to distinguish the different fibre components
  2. measuring crude fibre under-estimates the actual dietary fibre content of feed by up to 50%
    - since dietary fibre includes a variety of components, soluble fibres are lost
30
Q

What is NFE (digestible carbohydrate content?)

A

NFE = nitrogen free extract
- estimates starch and sugar content (digestible carbs)

31
Q

how can we calculate NFE%

A

%NFE = 100% - (5 components added together)

32
Q

Potential sources of error/limitations when calculating NFE

A
  • NFE accumulates all previous errors from analytical analysises
33
Q

What does the proximate analysis lack to provide information on?

A
  1. No info on the “digestibility” of food/feed
    - don’t know what will actually be absorbed by the organism
  2. No info on specific amino acids, minerals, lipids, or carbohydrates
    - this has prompted the development of more advanced assays
34
Q

what is the difference in calculations starting from wet weight vs. dry matter in proximate analysis?

A

wet weight: account for the original weight of the feed
dry matter: the % composition values will change but not the absolute amount in grams

35
Q

what are more accurate fibre analyses that can be used to complete the proximate analysis?

A
  • Van Soest Method
  • Southgate method
36
Q

Van Soest method for fibre analysis in feed

A
  • differentiates between insoluble fibres - Cellulose and hemicellulose - lignan (poorly fermented, prevents fermentation of other fibres)
  • determines fermentable and non-fermentable CHOs
  • not used for human food analysis because it poorly differentiates sugars, starches and soluble fibres
  • important for agriculture
37
Q

Southgate method for fibre analysis in feed

A
  • provides information about sugars, starch and various fibres
  • useful for human nutrition food labelling
  • doesn’t differentiate sufficiently between various insoluble fibre components adequately (therefore not used for agriculture)
38
Q

What component in the proximate analysis does each group on the food label come from?

A

fat = crude fat (ether extract)
carbohydrate = digestible CHO (NFE)
fibre = southgate analysis
protein = crude protein (Kjeldahl)

nutr 3210 (12 decks)

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