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Starch Digestion and Absorption in Nonruminants^1,2,3,

The Gastroenterology Division and The Digestive Disease Center, Stanford University School of Medicine, Stanford, CA 94305

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 1,4-linked glucose units (amylose) and 1,4-1,6-linked branched structure (amylopectin), is cleaved in the duodenal cavity by secreted pancreatic -amylase to a disaccharide (maltose), trisaccharide (maltotriose), and branched -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 -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.

KEY WORDS: • amylose • amylopectin • oligosaccharidase • disaccharidase • -amylase • glucose transport

¹ Presented at the 31st Annual Ruminant Nutrition Conference, entitled "Starch Digestion: Understanding and Potential for Improvement," at the Annual Meeting of the Federation of American Societies for Experimental Biology, April 1, 1990, Washington, DC.

² Guest editor for this symposium was C. B. Theurer, Department of Animal Sciences, University of Arizona, Tucson, AZ 85721.

³ Work of the author is supported by grants from the U.S. Public Health Service, National Institutes of Health for research (DK 11270) and for the Digestive Disease Center (DK 38707).

Manuscript received 26 June 1991. Revision accepted 16 July 1991.