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2. Food-Feeds Composition.doc

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Animal Science
ANSC 3120

Food/Feeds Composition  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 chemicals Or freeze Take Weight dry Take Weight  Determination of moisture allows further analysis to be a “Dry Matter” Basis  Potential Errors? 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 matter... Triglycerides – Mainly Fat Soluble vitamins Pigments (Chlorophyll) Waxes Some Phospholipids  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 Triglyceride o Cholesterol o Phospholipids o Fatty acids Proximate Analysis 2  Potential Errors? o Other lipid soluble compounds  Chlorophyll, etc  Waxes (usually small errors) o Use of ethers?  Very non-polar  Misses of a portion of phospholipids o Food labelling?  Total fat • PUFA • MUFA • Saturates • Trans Essential • Cholesterol Cardiovascular disease risk o Newer methods?  Chloroform methanol • Gas liquid chromatography o Fatty acid composition Organic Material is Lost Mineral Content • 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  Potential Errors? o Volatile Minerals?  Some loss of volatile minerals • Cl, Zn, Se o Individual minerals?  No data  Need Na data for food labelling  Atomic absorption  Danish Chemist: Johan Kjeldahl o Catlsberg Brewery Crude Protein Kjeldahl discovered that protein N content is fairly constant Kjeldahl Analysis: Crude Protein  Method: o Weighed and dried sample (1) digested with sulphuric acid o N co
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