Statistical optimization of a thermostable and neutral glucoamylase production by a thermophilic mold Thermomucor indicae-seudaticae in solid-state fermentation

Glucoamylase production by a thermophilic mold Thermomucor indicae-seudaticae was optimized in solid-state fermentation (SSF) by conventional 'one variable at a time approach' and further statistically using response surface methodology (RSM). Glucoamylase secretion was strongly affected by three variables (moisture ratio, inoculum level and incubation time), and therefore, these three factors were further optimized using response surface methodology. The glucoamylase production in flasks containing wheat bran, under the conditions optimized by RSM, was 455+/-23 U/g of dry moldy bran (DMB), while the predicted value by a polynomial model was 433.30 U/g DMB. The enzyme titre (455+/-23 U/g DMB) attained in the validation experiment of this investigation is higher than those reported in the literature. When the large-scale production was attempted in enamel trays, a marginally lower enzyme titres were attained. An overall 1.8-fold increase in glucoamylase production was achieved in SSF due to statistical optimization in comparison with that of 'one variable at a time' approach (250+/-13 U/g DMB). A 10-fold enhancement in glucoamylase production was recorded in SSF as compared to that in submerged fermentation.