Lecture 2 - Food/Feed Consumption Flashcards
What is the overview and order of proximate analysis
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)
What are the 5 things to be considered in proximate analysis
- moisture
- ether extract
- ash
- nitrogen
- crude fibre
Why is considering moisture important in feed
- water is weight
- water dilutes nutrients
- water plays a role in storage conditions
- water is important for optimal intake and performance of animals
What is the equation for moisture
% moisture = (wet weight - dry weight)/(wet weight)(x100)
What is equation for dry matter using moisture percentage
dry matter = 100% - %moisture
What is a potential source of error in determining moisture content
drying could potentially remove other crucial nutrients such as short-chain fatty acids and minerals
- would cause an underestimate of dry weight
What does measuring ether extract determine
fat content; crude or estimated fat
What is the equation for crude fat using ether extraction
% crude fat = (weight of ether extract)/(weight of wet sample)(x100)
What are some potential sources of error in determining crude fat
other things are soluble in organic solvents which could over-estimate crude fat determination
Why is it important to measure ash content
- nutritional labelling
- quality and taste of food
- microbiological stability
- nutritional requirements
- manufacturer processing
What does ash measure
mineral content
What is the equation for measuring ash (mineral content)
% ash = (weight of ash)/(weight of wet sample) (x100)
What are some potential sources of error in determining ash content
- volatile minerals could be lost when burning the residue
- no info about individual minerals, just the count as a whole
What does the Kjeldahl test determine
crude protein
What are the two assumptions made in the Kjeldahl analysis
- all nitrogen is in protein
- all protein contains 16% nitrogen
What are the 3 steps to the Kjeldahl analysis
- digestion - food sample is mixed into sulfuric acid which converts nitrogen to ammonia
- distillation - separates the ammonia
- titration - quantifies the amount of ammonia
What is the equation for calculating crude protein (Kjeldahl)
% crude protein = (N in sample x 6.25)/(wet weight of sample) (x100)
Where does the 6.25 come from in the crude protein calculation
100% protein/16% nitrogen (from the assumption that all protein have 16% nitrogen) = 6.25
What are some potential sources of error when calculation crude protein
- 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)
What is the equation for calculating crude fibre
% crude fibre = (weight of ash + crude fibre) - (weight of ash)/(wet weight of sample) (x100)
What is the difference between crude fibre and dietary fibre
crude = insoluble fibres
dietary = all fibres (soluble and insoluble)
Is crude an underestimation or overestimation of dietary fibre
underestimation
What are some potential sources of error in calculating crude fibre
- unable to distinguish between fibre components (crude and dietary)
- measuring crude underestimates the actual dietary fibre content by up to 50%
What are some examples of insoluble fibre (crude)
lignin, cellulose, hemicellulose
- remains intact through digestion (cannot dissolve)
