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)
What are some examples of soluble fibre
gums, pectins, mucilages
- forms gel (dissolves in water)
What is the equation for nitrogen free extract (digestible carbohydrate content)
% NFE = 100% - (% moisture + % crude fat + % ash + % crude protein + % crude fibre)
What are some potential sources of error when calculating nitrogen free extract (digestible carbohydrate content)
NFE accumulates all errors that exist in the other components
What is missing from the proximate analysis
- no info on digestibility
- no info on amino acids, minerals, lipids, or carbs
What are more accurate analyses to complement the proximate analysis
- Van Soest Method
- Southgate Method
What is an advantage of the Van Soest Method
differentiates between insoluble fibres
- cellulose and hemicellulose
- lignin
determines fermentedle and no-fermentable CHO
- important for agricultural applications
- fermentable = good, non-fermentable = not wanted
Why is the Van Soest Method not used in human food analysis
because it doesn’t differentiate sugars, starches, and soluble fibres
What is the advantage of the Southgate Method
provides info about sugars, starch, and various fibres
useful for human nutrition and food labelling*
What is the disadvantage of Southgate Method, and why is it not used in agriculture
doesn’t differentiate sufficiently between various insoluble fibres, so not used for agriculture
