Kinetic study of enzymatic hydrolysis of starch isolated from sorghum grain cultivars by various methods

Abstract

Sorghum (Sorghum bicolor (L.) Moench) crops as a source of starch was successfully cultivated in the Algerian Sahara. Starches from white and red sorghum grains were isolated under three steeping conditions for wet-milling process. The isolate starches susceptibility towards glucoamylase hydrolysis to glucose and the kinetic parameters (Km, Vmax, Kcat and Kcat/Km) are studied. The yield of starch isolation ranged from 40.37 to 54.79 %. The starch purity, amylose content, swelling power and water solubility index ranged from 90.00 to 99.08 %, 23.78 to 25.89 %, 10.37 to 12.47 g/g and 10.65 to 18.80 %, respectively. The values of Vmax in g.l−1.min−1 for starch isolated by three methods are 0.20, 0.09 and 0.058 for white grains and 0.10, 0.08 and 0.20 for red grains. The glucose concentration values in g.l−1 after 120 min of hydrolysis at the initial concentration of 20 g.l−1 of starch isolated by three methods are 13, 10.20 and 7.80 for white grains and 10, 13.80 and 11 for red ones. The results of kinetic study show that the hydrolysis of starch by glucoamylase from Aspergillus niger are affected by the source of starch and the conditions of starch isolation from grains.