Hydrolysis of Sorghum Grain Starch by Rumen Microorganisms and Purified Porcine α-Amylase as Observed by Scanning Electron Microscopy

Abstract

Scanning electron microscopy was used to observe endosperm structure and starch hydrolysis of three sorghum grain types (waxy, yellow endosperm, bird resistant). Split kernels were subjected to either rumen digestion for 75 min. to 8 hr. or hydrolysis by purified porcine α-amylase for 48 hours. Starch granules in soft endosperm of yellow and bird-resistant types were smooth and spherical; those in a waxy variety were irregular in shape. Split kernels immersed in rumen fluid for as little as 75 min. showed differential hydrolysis: point-surface attack on the starch from the waxy grain, linear track hydrolysis on that from the yellow endosperm, and minor point hydrolysis on that from the bird resistant type. Photomicrographs of split kernels suspended inside ruminally fistulated steers indicated different modes of starch attack. Surface attack on the waxy starch was mainly point hydrolysis with alternate layers digested inside the starch granule. Yellow endosperm starch was digested without structural resistance.