Production and Starch Saccharification by a Thermostable and Neutral Glucoamylase of a Thermophilic Mould Thermomucor Indicae-Seudaticae

The present investigation was aimed at producing a thermostable and neutral glucoamylase (amyloglucosidase, EC 3.2.1.3) by a thermophilic mould, Thermomucor indicae-seudaticae in submerged cultivation and testing its applicability in starch saccharification. Parametric optimization resulted in the secretion of 30,000 U/l of glucoamylase in a synthetic medium (5% soluble starch, 0.1% yeast extract, 0.05% K2HPO4 and 0.01% MgSO4· 7H2O) using 5 × 106 spores/50 ml of a 3-day-old inoculum at 40 °C and 250 rev/min in shake flasks in 48 h. The enzyme secretion was not affected to any significant extent by the tested additives and detergents. A 1.7-fold increase in glucoamylase secretion was attained when T. indicae-seudaticae was grown in a laboratory fermenter. The enzyme alone catalysed the hydrolysis of soluble starch to an extent of 65%. A prior treatment of starch with thermostable α-amylase and amylopullulanase, followed by glucoamylase, resulted in a greater extent of hydrolysis, 79 and 91%, respectively.