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Food Analysis > Lecture 4 - Moisture Analysis > Flashcards

Lecture 4 - Moisture Analysis Flashcards

(53 cards)

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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

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A

uses a chemical rxn in which water is involved

23
Q

describe physical methods

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A

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

24
Q

cons of drying methods?

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A

indirect

less specific to water

simple skills

25
3 types of drying methods?
1. oven drying 2. freeze drying 3. infrared drying
26
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
0.512 deg C | ie the boiling point increases as the removal of water increases = solute conc increases
27
moisture loss is a function of ___ and ___
time and temperature
28
types of ovens used in oven drying?
convection air forced microwave vacuum
29
in the temperature and %moisture relationship, the rise in temperature shows...
%mass loss (% moisture)
30
CHO breaks down at ___ and ____
higher temp and releases water
31
oxidation of FA could ____
increase weight of sample | this occurs in high fat foods
32
temperature and time that food stays in convection oven?
105-110 deg C 22-24 hours
33
disadvantages of convection oven drying?
longer analysis time loss of volatile components other than water larger temp gradient
34
describe forced air oven drying method
- 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
what is a possibility that occurs in forced air oven at high temp?
lipid oxidation leading to weight gain
36
describe microwave analyzer
- 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
describe vacuum oven
- 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
define boiling point
temp at which the vapor pressure of the liquid equals pressure surrounding the liquid
39
vacuum oven is based on the fat that...
water boils at lower temp under vacuum
40
what is the purpose of vacuum pump?
to reduce the oven's pressure to between 25-50 mmHg
41
role of drying agents in the vacuum oven method?
to dry the air for the vacuum pump to operate normally
42
components of vacuum oven?
vacuum oven vacuum pump drying agents
43
weight of a empty lab pan in the vacuum oven method?
20 grams
44
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
loss of wt = 25-24 = 1g moisture % = 1/5g x 100 = 20%
45
4 common drying agents for vacuum oven?
1. anhydrous CaCl2 (most safe) 2. anhydrous So3 3. phosphorus pentoxide P2O5 4 concentrated H2SO4 (most effective)
46
what is the most safe and most effective drying agents for vacuum ovens?
most safe: anhydrous CaCl2 | most effective: concentrated H2SO4
47
practical advantages of vacuum oven?
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
factors that affect oven drying methods?
1. temp 2. time 3. particle size
49
how does particle size affect drying?
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
describe infra red drying
- 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
what is a hygroscopic substance?
substance that absorbs moisture from air
52
describe rapid moisture analyzer tehcnologies
- 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
describe thermogravimetric analysis
- 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

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