Starch Digestion and Absorption in Nonruminants , ,

Abstract

Starch digestion and absorption is augmented appreciably by physical processing of grain or legume and by heating to 100°C for several minutes before its ingestion. Starch, a polysaccharide composed of α1,4-linked glucose units (amylose) and α1,4-1,6-linked branched structure (amylopectin), is cleaved in the duodenal cavity by secreted pancreatic α-amylase to a disaccharide (maltose), trisaccharide (maltotriose), and branched α-dextrins. These final oligosaccharides are hydrolyzed efficiently by complimentary action of three integral brush border enzymes at the intestinal surface: glucoamylase (maltase-glucoamylase, amyloglucosidase), sucrase (maltase-sucrase) and α-dexitrinase (isomaltase). The final monosaccharide glucose product is then cotransported into the enterocyte along with Na⁺ by a specific brush border 75-kDa transport protein in the rate-limiting step for overall starch assimilation. By virtue of this sequential luminal and membrane digestion followed by glucose transport, starch is assimilated in a very efficient manner in nonruminants.