Improving production of hyperthermostable and high maltose-forming α-amylase by an extreme thermophile Geobacillus thermoleovorans using response surface methodology and its applications

Abstract

By cultivating Geobacillus thermoleovorans in shake flasks containing cane molasses medium at 70 °C, the fermentation variables were optimized by ‘one variable at a time’ approach followed by response surface methodology (RSM). The statistical model was obtained by central composite design (CCD) using three variables (cane-molasses, urea and inoculum density). An overall 1.6- and 2.1-fold increase in enzyme production was achieved in the optimized medium in shake flasks and fermenter, respectively. The α-amylase titre increased significantly in cane-molasses medium (60 U ml −1) as compared to that in the synthetic medium (26 U ml −1). Thus the cost of enzyme produced in cane molasses medium (€0.823 per million U) was much lower than that produced in the synthetic starch–yeast extract-tryptone medium (€18.52 per million U). The shelf life of bread was improved by supplementing dough with α-amylase, and thus, the enzyme was found to be useful in preventing the staling of bread. Reducing sugars liberated from 20% and 30% raw pearl millet starch were fermented to ethanol; ethanol production levels attained were 35.40 and 28.0 g l −1, respectively.