Amylolysis of amylopectin and amylose isolated from wheat, triticale, corn and barley starches

Amylopectin (AP) and amylose (AM) were isolated from normal (wheat, triticale, corn, and barley), waxy (corn and barley), and high-amylose (corn and barley) starches. The relationship between the molecular characteristics of the above starch polymers and amylolysis was studied in comparison to their native granules. Amylolysis was conducted by using granular starch hydrolyzing enzymes (a mixture of alpha-amylase and glucoamylase) at sub-gelatinization temperatures (<55 degrees C) over a period of 1 to 72 h, and the degree of hydrolysis (DH) was measured as a percentage of reducing value. At the early stages (1 h) of hydrolysis, AP and AM fractions from all starches were significantly hydrolyzed by amylases to a greater extent than native granules. Regardless of starch sources, the DH of AP and AM at 1 h hydrolysis ranged from 71.4 to 86.1 and 66.4 to 81.4%, respectively. Between 1 and 72 h of hydrolysis, the DH of AP was higher than AM in normal and high-amylose starches. Significant correlations were found between the molecular weight (M-w) or molecular size (R-z) of AP, and the DH of native granules at 1 h hydrolysis. The results suggested that a high proportion of short-chains in AP, indicated by its high M-w, high R-z and low average chain-length, were responsible for high DH of native granules. The difference in DH among native granules was mainly influenced by the difference in granular architecture resulting from variations in average chain length of AP. (C) 2013 Published by Elsevier Ltd.