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Food Analysis > Lecture 4 - Moisture Analysis > Flashcards

Lecture 4 - Moisture Analysis Flashcards

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1
Q

what are the 5 components in a proximate analysis?

A 
moisture
ash
protein
fibre
fat
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2
Q

why is CHO usually not included in proximate analysis?

A

it exists in different forms

difficult to analyze

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3
Q

how is %CHO measured?

A

by difference of measured other components

%CHO= 100- (%H2O+ %Ash+ %Protein+ %Fibre+ %Fat)

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4
Q

what is food broken down into?

A

dry matter + H2O

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5
Q

what is dry matter broken down into?

A

organic + inorganic (ash)

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6
Q

what is organic matter broken down into?

A

non nitrogenous components and N containing components (crude protein)

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7
Q

what is non-nitrogenous components broken down into?

A

non fatty components and fatty components (fat)

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8
Q

what is non fatty components broken down into?

A

CHO and fiber

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9
Q

role of water in food produce?

A
  • provides structure
  • standard of identity (need to have certain amount of water)
  • cheap filler (economic relevance)
  • undesired in dry products
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10
Q

role of dry matter in food?

A
  • often the expensive part
  • defines the nutritional part
  • convenient for transport
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11
Q

define moisture determination

A

most widely used analytical measurements in processing and testing of food products

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12
Q

why is it important to measure moisture in food materials?

A
  • food safety (mold growth produces aflatoxins)
  • shelf life and stability
  • food quality
  • economic considerations
  • government regulations (ie standardized foods)
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13
Q

common levels of moisture in food materials?

A
  1. high moisture foods
  2. intermediate moisture
  3. low moisture
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14
Q

4 forms of water in food?

A
  1. free water/bulk water
  2. capillary or trapped water
  3. physically bound water
  4. chemically bound water
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15
Q

define free/bulk water

A
  • water in food that is free from other constituents
  • each h2o molecule is surrounded only by other h2o molecules
  • physicochemical properties that are the same as pure water (ie mp, bp, density, compressibility, heat of vaporization, electromagnetic absorption spectra)
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16
Q

describe capillary/trapped water

A
  • water held in narrow channels formed by physical barriers by capillary forces
  • has physicochemical properties similar to bulk water
  • ie water in a plant cell
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17
Q

describe physically bound water

A
  • water that is physically bound w/ other molecules (ie proteins)
  • has different physicochemical properties than free water
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18
Q

describe chemically bound water

A
  • ie salts such as Na2SO4 . 10H2O

- different properties to free water

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19
Q

4 methods for measurement of moisture in foods

A
  1. drying methods
  2. distillation methods
  3. chemical methods
  4. physical methods
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20
Q

describe drying methods

A

removal of water in form of water vapour

the lost of weight is taken as a measure of moisture content

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21
Q

describe distillation methods

A

removal of water by distillation process

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22
Q

describe chemical methods

A

uses a chemical rxn in which water is involved

23
Q

describe physical methods

A

takes advantage of physical properties of water (ie electrical or dielectric properties)

24
Q

cons of drying methods?

A

indirect

less specific to water

simple skills

25
Q

3 types of drying methods?

A
  1. oven drying
  2. freeze drying
  3. infrared drying
26
Q

according to Raoult’s law, the BP of water increases ___ for every 1 molecular weight of a solute is dissolved in 1.0L of water

A

0.512 deg C

ie the boiling point increases as the removal of water increases = solute conc increases

27
Q

moisture loss is a function of ___ and ___

A

time and temperature

28
Q

types of ovens used in oven drying?

A

convection
air forced
microwave
vacuum

29
Q

in the temperature and %moisture relationship, the rise in temperature shows…

A

%mass loss (% moisture)

30
Q

CHO breaks down at ___ and ____

A

higher temp and releases water

31
Q

oxidation of FA could ____

A

increase weight of sample

this occurs in high fat foods

32
Q

temperature and time that food stays in convection oven?

A

105-110 deg C

22-24 hours

33
Q

disadvantages of convection oven drying?

A

longer analysis time

loss of volatile components other than water

larger temp gradient

34
Q

describe forced air oven drying method

A
  • air circulated by a fan
  • temp can be higher and time can be shorter (135degC for 4h)
  • temp differential not >1degC
  • process is faster, efficient and water vapour will not condense due to fan
35
Q

what is a possibility that occurs in forced air oven at high temp?

A

lipid oxidation leading to weight gain

36
Q

describe microwave analyzer

A
  • rapid technique. allows in process analysis
  • has in-built microbalance that monitors weight loss
  • microwave energy and time have to be defined to ensure accurate measurement
  • pan used should not absorb microwave energy (fiberglass and quartz fiber)
  • not approved method for moisture analysis
37
Q

describe vacuum oven

A
  • drying under reduced pressure (22-100mm Hg)
    -fast rate of evaporation
    -removal of water with out decompoisition
    -temp 95-102 degC
    temp for high sugar products: 60-70degC
38
Q

define boiling point

A

temp at which the vapor pressure of the liquid equals pressure surrounding the liquid

39
Q

vacuum oven is based on the fat that…

A

water boils at lower temp under vacuum

40
Q

what is the purpose of vacuum pump?

A

to reduce the oven’s pressure to between 25-50 mmHg

41
Q

role of drying agents in the vacuum oven method?

A

to dry the air for the vacuum pump to operate normally

42
Q

components of vacuum oven?

A

vacuum oven

vacuum pump

drying agents

43
Q

weight of a empty lab pan in the vacuum oven method?

A

20 grams

44
Q

using the vacuum method, what is the moisture%?

wt of empty pan = 20g
wt of wheat sample = 5g
wt of wheat and pan after drying = 24g

A

loss of wt = 25-24 = 1g

moisture % = 1/5g x 100 = 20%

45
Q

4 common drying agents for vacuum oven?

A
  1. anhydrous CaCl2 (most safe)
  2. anhydrous So3
  3. phosphorus pentoxide P2O5
    4 concentrated H2SO4 (most effective)
46
Q

what is the most safe and most effective drying agents for vacuum ovens?

A

most safe: anhydrous CaCl2

most effective: concentrated H2SO4

47
Q

practical advantages of vacuum oven?

A
  1. reduced temp in drying chamber = reduction in loss of volatiles (non water components) and less effect on degradation of some components (ie sugars, especially fructose)
  2. shortened analysis time (3-8h)
48
Q

factors that affect oven drying methods?

A
  1. temp
  2. time
  3. particle size
49
Q

how does particle size affect drying?

A

smaller particles = surface area will be larger = loss of water will be effective

in small particles, the distance that water molecules will migrate are smaller than surface where they will be lost

50
Q

describe infra red drying

A
  • penetrating infrared rays dries the sample
  • short drying time: 10-25min
  • heat of infrared lamp: 1730-2230 deg C
  • infrared drying ovens can be equipped with an analytical balance to read moisture content directly
  • not an approved drying technique by AOAC international
51
Q

what is a hygroscopic substance?

A

substance that absorbs moisture from air

52
Q

describe rapid moisture analyzer tehcnologies

A
  • quick decision making
  • uses halogen or ceramic heaters
  • uses aluminum pans
    usual temp: 25 to 275 deg C
  • uses digital balance and automatic weights to calculate %moisture
  • con: increases possibility of error
53
Q

describe thermogravimetric analysis

A
  • mass of sample continuously measured as it’s heated at a controlled rate in a controlled atmosphere
  • inert gas (ie N) is used to avoid oxidation and gain mass
  • can acquire higher temp, thus can be used for measuring decomposition and weight % ash

Food Analysis (17 decks)

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