Inhibition of enzymic digestion of amylose by free fatty acids in vitro contributes to resistant starch formation.

The effect of lipids on the enzymic breakdown of starch was investigated using an in vitro assay system. Mixtures of potato amylose, amylopectin and starch and various lipids were incubated at 37 degrees C for 10 min and subjected to digestion by alpha-amylase (EC 3.2.1.1) and amyloglucosidase (EC 3.2.1.33). Lauric, myristic, palmitic and oleic acids and lysolecithin inhibited enzymic hydrolysis of amylose by approximately 35% (P < 0.05). Stearic acid and cholesterol had no effect on the enzymic breakdown of amylose. Retrograded amylose was hydrolyzed less readily (P < 0.05) than solubilized amylose, but the breakdown was not further inhibited in the presence of lauric acid. Fatty acids had no effect on the enzymic hydrolysis of amylopectin, whereas inhibition by fatty acids of the breakdown of whole starch was consistent with only the amylose fraction being affected. The possibility that interactions between starch and fatty acids in the digestive tract could contribute to the formation of resistant starch is considered.