Lecture 2 - Food/Feed Consumption

Question 1

What is the overview and order of proximate analysis

Answer 1

start with feed sample (wet weight)
air dry it to get dry matter (1. moisture)
from dry matter: ether extraction (2. ether extract)
ignite ether extraction (3. ash)
from dry matter: kjeldahl test (4. nitrogen)
from dry matter: ether extraction, boil in acid, gain residue, boil in alkali, gain residue, ignite, get ash and crude fibre (5. crude fibre)

Question 2

What are the 5 things to be considered in proximate analysis

Answer 2

1. moisture
2. ether extract
3. ash
4. nitrogen
5. crude fibre

Question 3

Why is considering moisture important in feed

Answer 3

• water is weight
• water dilutes nutrients
• water plays a role in storage conditions
• water is important for optimal intake and performance of animals

Question 4

What is the equation for moisture

Answer 4

% moisture = (wet weight - dry weight)/(wet weight)(x100)

Question 5

What is equation for dry matter using moisture percentage

Answer 5

dry matter = 100% - %moisture

Question 6

What is a potential source of error in determining moisture content

Answer 6

drying could potentially remove other crucial nutrients such as short-chain fatty acids and minerals
- would cause an underestimate of dry weight

Question 7

What does measuring ether extract determine

Answer 7

fat content; crude or estimated fat

Question 8

What is the equation for crude fat using ether extraction

Answer 8

% crude fat = (weight of ether extract)/(weight of wet sample)(x100)

Question 9

What are some potential sources of error in determining crude fat

Answer 9

other things are soluble in organic solvents which could over-estimate crude fat determination

Question 10

Why is it important to measure ash content

Answer 10

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

Question 11

What does ash measure

Answer 11

mineral content

Question 12

What is the equation for measuring ash (mineral content)

Answer 12

% ash = (weight of ash)/(weight of wet sample) (x100)

Question 13

What are some potential sources of error in determining ash content

Answer 13

• volatile minerals could be lost when burning the residue
• no info about individual minerals, just the count as a whole

Question 14

What does the Kjeldahl test determine

Answer 14

crude protein

Question 15

What are the two assumptions made in the Kjeldahl analysis

Answer 15

1. all nitrogen is in protein
2. all protein contains 16% nitrogen

Question 16

What are the 3 steps to the Kjeldahl analysis

Answer 16

1. digestion - food sample is mixed into sulfuric acid which converts nitrogen to ammonia
2. distillation - separates the ammonia
3. titration - quantifies the amount of ammonia

Question 17

What is the equation for calculating crude protein (Kjeldahl)

Answer 17

% crude protein = (N in sample x 6.25)/(wet weight of sample) (x100)

Question 18

Where does the 6.25 come from in the crude protein calculation

Answer 18

100% protein/16% nitrogen (from the assumption that all protein have 16% nitrogen) = 6.25

Question 19

What are some potential sources of error when calculation crude protein

Answer 19

• assuming all protein has 16% nitrogen is only an estimate, the actual range is 13-19%
• doesn’t consider other sources of nitrogen (not all nitrogen comes from protein)

Question 20

What is the equation for calculating crude fibre

Answer 20

% crude fibre = (weight of ash + crude fibre) - (weight of ash)/(wet weight of sample) (x100)

Question 21

What is the difference between crude fibre and dietary fibre

Answer 21

crude = insoluble fibres
dietary = all fibres (soluble and insoluble)

Question 22

Is crude an underestimation or overestimation of dietary fibre

Answer 22

underestimation

Question 23

What are some potential sources of error in calculating crude fibre

Answer 23

• unable to distinguish between fibre components (crude and dietary)
• measuring crude underestimates the actual dietary fibre content by up to 50%

Question 24

What are some examples of insoluble fibre (crude)

Answer 24

lignin, cellulose, hemicellulose
- remains intact through digestion (cannot dissolve)

Question 25

What are some examples of soluble fibre

Answer 25

gums, pectins, mucilages
- forms gel (dissolves in water)

Question 26

What is the equation for nitrogen free extract (digestible carbohydrate content)

Answer 26

% NFE = 100% - (% moisture + % crude fat + % ash + % crude protein + % crude fibre)

Question 27

What are some potential sources of error when calculating nitrogen free extract (digestible carbohydrate content)

Answer 27

NFE accumulates all errors that exist in the other components

Question 28

What is missing from the proximate analysis

Answer 28

• no info on digestibility
• no info on amino acids, minerals, lipids, or carbs

Question 29

What are more accurate analyses to complement the proximate analysis

Answer 29

1. Van Soest Method
2. Southgate Method

Question 30

What is an advantage of the Van Soest Method

Answer 30

differentiates between insoluble fibres
- cellulose and hemicellulose
- lignin
determines fermentedle and no-fermentable CHO
- important for agricultural applications
- fermentable = good, non-fermentable = not wanted

Question 31

Why is the Van Soest Method not used in human food analysis

Answer 31

because it doesn’t differentiate sugars, starches, and soluble fibres

Question 32

What is the advantage of the Southgate Method

Answer 32

provides info about sugars, starch, and various fibres
useful for human nutrition and food labelling*

Question 33

What is the disadvantage of Southgate Method, and why is it not used in agriculture

Answer 33

doesn’t differentiate sufficiently between various insoluble fibres, so not used for agriculture