food analysis
development, application, and study of analytical methods for characterizing foods and their constituents
Feed Sample
Wet weight, original food sample
Use this in the denominator of calculations!
- Moisture (refer to diagram in slides)
moisture content
wet weight - dry matter weight = moisture content
%moisture = (wet weight - dry weight / wet weight) x 100%
%dry matter = 100 - % moisture
- Moisture: Potential Sources of Errors/Limitations
drying can remove other volatile compounds (eg. SCFA and some minerals) = causes slight UNDER-ESTIMATION of dry weight
- Ether Extract (Crude Fat) (refer to diagram in slides)
approximating fat
%crude fat = (weight of ether extract / wet weight of sample
- Ether Extract: Potential Sources of Errors/Limitations
other things are soluble in ether extract:
chlorophyll, resins, waxes in plants (NOT NUTRIENTS)
generalized method - doesn’t tell exact composition of fats, only total amount of fats
OVER-ESTIMATION of crude fat
- Ash (mineral content) (refer to diagram in slides)
%Ash = (weight of ash / wet weight of sample) x 100%
ignite precipitate from ether extraction (residue)
measure of nonspecific inorganic components
- Ash: Potential Sources of Errors/Limitations
volatile minerals may be lost when burning residue
UNDER-ESTIMATION
no info about specific/individual minerals, only total mineral content
- Nitrogen (Crude Protein) (refer to diagram in slides)
Kjeldahl Analysis
%crude protein = (N in sample x 6.25 / wet weight of sample x 100%
where do we get 6.25? Kjeldahl Analysis Assumption all protein has 16% nitrogen, therefore
100% (total protein) / 16% (nitrogen) = 6.25
if different percentage nitrogen, divide 100 b that value
- Nitrogen: Potential Sources of Errors/Limitations
- Assumes all proteins have 16% nitrogen (actual range is 13-19%)
- other sources of nitrogen (nitrates, nitrites, urea, nucleic acids, etc in food sample would be part of calculation)
OVER-ESTIMATION
- Crude Fibre (refer to diagram in slides)
%crude fibre = [((weight of ash + crude fibre) - (weight of ash)) / wet weight of sample] x 100%
crude fibre is not the same as dietary fibre, crude fibre is cellulose and lignin
dietary fibre = all fibre, both soluble and insoluble, in a food, additional analysis needed to calculate
UNDER-ESTIMATION : up to 50% because soluble fibre is lost during proximate analysis
one of the biggest errors (second biggest)
Dietary Fibre
Non-digestible complex CHO (carbohydrate)
structural part of plants
Soluble and Insoluble
Soluble Fibre
Forms a gel
does dissolve in water
eg. pectins, gums, mucilages
Insoluble Fibre
Remains intact through intestinal tract
does not dissolve in water
eg. cellulose, lignin, hemicellulose
Nitrogen Free Extract (NFE) = Digestible Carbohydrate (CHO)
estimates starch and sugar content
%NFE = 100 - (%moisture + %crude fat + %ash + %crude protein + %crude fibre)
Nitrogen Free Extract (NFE): Potential Sources of Errors/Limitations
NFE accumulates all of the errors that exist for the other components
LARGEST ERROR
