Nutrient analyses
6 important questions on Nutrient analyses
N-containing matter (crude protein)
- but all proteins are made of amino acids containing an amine-group (-NH2)
- Kjeldahl procedure = based on digestion of the sample in concentrated sulphuric acid + potassium or sodium sulphate + catalyst to convert all nitrogen within the material to ammonium
- average protein = 16% N -> 6.25(100/16)
- milk protein = 6.38
- This method is not specific for protein but determines all components which contain an amine group (urea, ammonia and nucleic acid)
Additional analytical methods
- This fraction contains mainly carbohydrates
- large difference in the digestibility of these compounds -> additional analytical methods have been developed
Analytical methods carbohydrates
- non-structural = starch and sugars that can be digested by animals using endogenous enzymes + have a high nutritional value
- structural carbohydrates = located in the cell wall of plant material + can only be digested by microbes
- fermentation = digestion performed under anaerobic conditions
- further division can be made based on the solubility
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Analytical methods starch and sugars
- starch is a polymer containing a large amount of glucose
- can be digested by the enzyme alpha-amylase -> breaks the binding between the molecules -> releasing the glucose which can be absorbed by the animal
- content of free sugars is less than starch, but is has a high nutritional value
- determination of free sugars -> based on the reduing capacity, which is measured by a specific color reaction
Analytical methods structural carbohydrates (fibre)
- Van soest -> fractionation by solubilization
- Starts with mild extraction of the sample with neutral detergent -> residue after ash correction was termed neutral detergent fibre (NDF) -> further fractionation by a extraction with acid -> risue after ash corretion -> acid detergent fibre (ADF)
- difference between NDF and AFD is hemicellulose
- acid detergent lignin (ADL) contains lignin
- difference between ADF and ADL is cellulose
Amico acids, fatty acids and sugars
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