Starch: Granule, Amylose-Amylopectin, Feed Preparation, and Recovery by the Fowl's Gastrointestinal Tract

Abstract

SUMMARY Starch exists as glucose polymers of amylose and amylopectin. Amylose involves 10–30 glucose units having α-1,4-linkages enabling self-association into a helix. Amylopectin is assembled from a large number of helices interconnected by α-1,6-branching to dominate each granule. Granules have amorphous branching alternate with layers of crystallized helices. Crystallization involves helices laterally held together with either intermediary water (A) or is direct H-bonded (B) to resist digestion. Granule digestion by α-amylase depends on attachment along the helix length with release of maltose and maltotriose which includes α-limit dextrins from amylopectin. Amyloplasts progressively assemble each granule with sequential cell filling from aleurone to core during endosperm maturation. Incomplete development reduces endosperm starch content and energy value while losses from germination are less influential. High temperature drying of moist grain creates resistant granules due to annealing and partial loss of bound water from A- to form H-bonding and B-crystals. Further annealing and additional resistance occurs with high temperature pelleting. Extrusion extends annealing together with granule gelatinization which frees polymers enabling retrogradion into resistant crystallites of amylose while amylopectin remains amorphous and digestible. Pellet stability reduces feed loss and work of prehension. Gastric digestion improves granule exposure. Pancreatic α-amylase erodes granules within the small intestine with products transferring to the unstirred water layer where microvilli enzymes generate glucose for absorption. Resistance delays granule erosion with potential continuance and fermentation in the large intestine that reduces NE then AME if excreted. Starch resistance influences location of digestion by the gastrointestinal tract and product use.