Proximate Analysis (6 major classes of food chemicals)
o Southgate Method
o Van Soest Method Further analysis of CHO/fibre
Proximate Analysis – Germany 1865!
6. Nitrogen Free-extract (by subtraction) st
Crude by modern analytical standards but a 1 step in understanding food is a collection of
Or freeze Take Weight
Determination of moisture allows further analysis to be a “Dry Matter” Basis
o Drying removes other volatile components
Eg Volatile fatty acids (2 – 4C); alcohols
Proximate Analysis 1 Therefore overestimating of moisture
Not used in human food labelling!
o Human food labelled on an ‘as is basis’
Widely used in agriculture
o More accurate to formulate diets on a dry matter basis
o Dry matter would be confusing for people looking at products in stores
Now, you have a
sample of dry
Triglycerides – Mainly
Fat Soluble vitamins
Weighed and dried sample is extracted with ether (organic solvent)
Ether fraction transferred to new tube and dried
Leaves fatty residue to be weighed
Ether Extract: Crude Fat
Crude fat meant to be:
o Fatty acids
Proximate Analysis 2 Potential Errors?
o Other lipid soluble compounds
Waxes (usually small errors)
o Use of ethers?
Misses of a portion of phospholipids
o Food labelling?
• Trans Essential
Cardiovascular disease risk
o Newer methods?
• Gas liquid chromatography
o Fatty acid composition
Material is Lost
• Cl, Zn, Na, Se, Fe, K, Ca, P, Mg, Cr, Mn, F, Mb, etc
Proximate Analysis 3 Ash: Mineral Content
% Ash = Weight of ash_____ X 100%
Wet Weight of Sample
o Volatile Minerals?
Some loss of volatile minerals
• Cl, Zn, Se
o Individual minerals?
Need Na data for food labelling
Danish Chemist: Johan Kjeldahl
o Catlsberg Brewery
Kjeldahl discovered that protein
N content is fairly constant
Kjeldahl Analysis: Crude Protein
o Weighed and dried sample (1) digested with sulphuric acid
o N co