第四章 碳水化合物Carbohydrates 2013.ppt

LIGNIN 5. Increases with plant maturity 6. Indigestible by animals and bacteria Why Fiber Content of Animal Feeds Is Important Fiber analyses is one means of estimating the nutritional value of feedstuffs. As fiber content increases, nutritional value decreass Fiber is found only in plants, primarily in the cell walls. Plant Cell Walls Plant cell walls Crude Fiber Sample Boiled 30 min. in 1.25% H2SO4 Filtered Residue Solubles Boiled 30 min. in 1.25% NaOH Residue Solubles Filtered Burned Crude Fiber Ash Dried Fat removed by Extracted with ether Crude Fiber Assumes material not soluble in weak acid and base are “fiber”. Oldest system still in use; originally developed in mid 1800’s. Crude fiber does a poor job of quantifying the fiber content of feeds, hemicelluloses are not measured. It is still used to guarantee maximum fiber content in commercial animal feeds. Van Soest Method Sample Heated in a neutral detergent solution (pH 7.0) for 1 hour Filtered Neutral Detergent Fiber (NDF) (cell walls-cellulose, hemicellulose, legnin + ash) Cell contents and pectin (protein, lipids, and soluble CHO) Heated in acid detergent solution, (1N H2 SO4) for 1 hour Filtered Hemicellulose Acid Detergent Fiber (ADF) (cellulose, lignin, ash) 72% H2 SO4 Cellulose Lignin + ash Lignin Ash Burn Van Soest Method Separates cell walls (total fiber) from cell contents then separates out the parts of fiber Most common method of determining fiber in animal feeds NDF is the best indicator of total fiber content in animal feeds ADF is commonly used as a predictor for digestibility (energy content) of forages, because it contains the two least digestible fractions of fiber Dietary Fiber Sample Ether extraction Lipids Residue Heat stable amylase Protease Amyloglucosidase These enzymes mimic digestion in the stomach and small intestine of humans. Ethanol to precipitate soluble fiber Soluble sugars and proteins Filter Residue Burn part of residue to determine ash Part of residue is analyzed t