Term
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Definition
| NFE = 100 –(CP + EE + CF + Ash + Moisture) |
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Term
| pros of the proximate analysis system |
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Definition
–Basic overview, useful for many years
–Cheap
–Rapid
–Easily understood |
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Term
| cons of the proximate analysis system |
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Definition
| Inaccurate quantificationof nutritional entities |
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Term
| some oven drying methods in the proximate analysis system |
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Definition
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Term
| what oven drying measures |
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Definition
| DM c'tration, not moisture c'tration |
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Term
| some problems with moisture assay |
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Definition
-Destructive
-VFAs, NH3& alcohols lost during oven drying at 105°C
-grainsOven-drying only measures physically boundwater
-Drying above 60°C can create artifacts that hinder lignin, fiber & ADF analysis |
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Term
| some alternative DM methods |
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Definition
-Correction equations
-Freeze drying (lyophilizing )
-Slow, low temperature drying e.g. 55oC for 48 h |
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Term
| some alternative moisture methods |
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Definition
-Toluene distillation
-Karl Fischer Titration (The reference method)
-Gas chromatography
-Saponification |
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Term
| some problems wigth EE assay |
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Definition
-Assumed to represent ‘high energy’ components i.e. true fat & oil content (2.5 x energy of carbs)
-Includes complex lipids that are low in energy
+E.g. waxes, pigments, fat-soluble vitamins, sterols
-Some are not digestiblee.g. waxes
-May include protein & other ether-soluble, non fat compounds e.g. chlorophyll, resins etc. |
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Term
| some problems with ash assays |
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Definition
-Excludes volatile mineralseg. I & Se, Cl & Zn
-May include sand & other inorganic elementsof organic origin e.g. P & S from proteins
-Doesn’t identify individual minerals
-Use atomic absorption spectrophotometer to accurately quantify minerals |
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Term
| some problems with CF assays |
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Definition
-Contains some lignin, cellulose, & hemicellulose
-Excludes some fiber fractions
+(included in NFE fraction)
+Cellulose, lignin
-Doesn’t reflect the different types of fiber e.g. cellulose, hemicellulose, lignin |
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Term
| some problems with CP assays |
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Definition
Determined by Kjeldahlanalysis which:
–Ignores nitrates
–Does not indicate unavailable fiber-bound / heat damaged protein
–Is based on some questionable assumptions |
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Term
| some Assumptions of Kjeldahl analysis |
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Definition
1.All proteins contain 16%N
Hence uses constant ‘6.25’ to convert N to protein
2.All N in the food comes from true protein |
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Term
| are all amino acids created equal? |
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Definition
| no, some have higher N content than others |
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Term
| some nitrogenous compounds in plants |
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Definition
-Nucleic Acids (DNA/RNA)
-Cell Wall Proteins
-Nitrogenous Lipids
-Ammonium Salts
-Secondary Compounds
-Free Amino Acids
-Peptides
-Protein |
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Term
| some alternatives to CP methods to get the true protein values |
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Definition
1.Combustion methods (e.g. LECO analyzers)
2.Ninhydrin analysis
3.Trichloroacetic acid (TCA) precipitation
4.Colorimetric/ dye binding techniques |
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Term
| some info about Combustion methods (e.g. LECO analyzers) |
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Definition
–Based on the Dumas (1831) Combustion method
–Sample N burnt to elemental N; measured by thermal conductivity
Pros:
–More repeatable/ precise, (error =0.9 vs 0.14 for kjeldahl)
–No reagents; less hazardous,
–1.5-2% better estimates of sample N
–Quicker; easier
Cons:
–Small sample size problems (now solved)
–May need dried sample (now solved) |
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Term
| some info about Ninhydrin analysis |
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Definition
–Involves hydrolyzing protein to aas &
–Adding ninhydrin which:
–reacts with a-amino acids to produce a purple color.
–Color intensityreflects amino acid concentration.
–The test is sensitive but the reagent is difficult to prepare |
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Term
| some info about Trichloroacetic acid (TCA) precipitation |
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Definition
–TCA precipitates proteinin a liquid e.g. milk
–Protein is filtered off, NPN is retained in filtrate
–Maceration may be required to free fiber-boundprotein |
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Term
| some info about Colorimetric/ dye binding techniques |
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Definition
–Lowry method, Bio-rad, Bradford’s assay etc.
–Involve reactions between peptide N, or acidic or basic aas with a dye
–Measure soluble/availableN
–Appropriateness for forages with fiber / tannin bound N
–Results may depend on particle size and peptide size, presence of reagents that interfere with the reaction |
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Term
| some problems with NFE calculation |
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Definition
-Not directly measured, calculated by difference
-NFE is a very vague measure of several constituents
-It should estimate non-fiber carbohydrates but does not do this accurately
-Often includes cell wallcomponentsMay be less digestible than CF
-Transfer errors |
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Term
| proximate analysis doesn’t account for... |
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Definition
| fecal, urine and gaseous losses. |
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Term
| proximate analysis ignores... |
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Definition
| palatability, digestibility, toxicity etc |
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Term
| most labs have replaced aspects of the Proximate analysis system with... |
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Definition
| modern analytical techniques |
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