Drying can remove other volatile compounds such as short chain fatty acids

Drying can remove other volatile compounds such as

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Drying can remove other volatile compounds, such as short chain fatty acids (SCFAs) and some minerals (more important from agricultural standpoint) o This can cause a slight under-estimation of dry weight 5
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Differences between human and agricultural application? - Agricultural industry more interested in composition of dry matter (all the nutrients for the animals) - Human food labelling is based on wet weight 2. Ether Extract (Crude Fat) % crudefat = weight of crude fat wet weight of sample × 100% Potential sources of error/limitations: - Other things are soluble in ether extract: o Ex. Chlorophyll, resins, waxes in plants (which are not nutrients) o This will over-estimate crude fat determination Changes in current food labeling - Newer and more sensitive methods now exist (gas chromatography) 3. Ash (Mineral Content) 6
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% Ash = weight of ash wet weightof sample × 100% Potential sources of error / limitations: - Volatile minerals may be lost when burning the residue - No information about individual minerals **** it is now mandatory for food labels to indicate sodium content 7
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4. Nitrogen (Crude Protein) Three Main Steps to the Kjeldahl Analysis: 1. Digestion – A food smaple is mixed with sulfuric acid, which converts nitrogen into ammonia (titrate ammonia is a proxy for the amount of nitrogen) 2. Distillation – separates the ammonia 3. Titration – quantifies the amount of ammonia % crude protein = ( N sample× 6.25 wet weightof sample ) × 100% Where do we get 6.25? - Kjeldahl Analysis Assumption: *** ALL protein has 16% nitrogen*** - 100% (total protein) ÷ 16% (nitrogen) = 6.25 - Therefore: o Nitrogen x 6.25) = Crude Protein Kjeldahl Analysis Potential sources of error / limitations: 1. Assumes all proteins have 16% nitrogen - Actual range is 13-19% o Ex. Peanuts have ~18% nitrogen … therefore conversion factor = 5.5 o Ex. Milk has 15.7% nitrogen… therefore conversion factor = 6.38 2. Other sources of nitrogen - Any nitrates, nitrities, urea, nucleic acids, etc. in the food sample would therefore be part of the crude protein calculation *This would slightly over-estimate crude protein content SAMPLE QUESTION What is the conversion factor to be used if a food product has 20% nitrogen? 100% protein ÷ 20% nitrogen = 5.0 8
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So the new equation to determine crude protein would be… % crude protein = N sample× 5.0 wet weight of sample × 100% 5. Crude Fibre (Fibre) % CRUDE FIBER = ( wt of ASH + Crude Fiber ) ( wt of ASH ) wet weight of sample × 100% “Crude fibre” is not the same thing as “dietary fibre” - Crude fibre is mainly cellulose and lignan (i.e., what remians afer procesing in the proximate analysis) o Soluble fibres are mostly lost during the analysis - Whereas dietary fibre is for ll fibre (both soluble and insoluble) (to get dietary fibre you need complementry processes to find them out since some are soluble) Potential sources of error / limitations: - Unable to distinguish different fibre components - Measuring crude fibre uner-estimates the actual dietary fibre content of feed by up to 50%.
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