Production of raw-starch-digesting α-amylase isoform from Bacillus sp. under solid-state fermentation and biochemical characterization

Abstract

α-Amylase production by solid-state fermentation of different Bacillus sp. was studied previously on different fermentation media. However, no study has been reported on the influence of selected media on expression of desired amylase isoforms such as raw-starch-digesting amylase (RSDA). In this paper, the influence of different inexpensive and available agro-resources as solid media (corn, wheat and triticale) on α-amylase isoform induction from three wild-type Bacillus sp., selected among one hundred strains tested, namely 9B, 12B and 24A was investigated. For all three strains, tested amylases were detected in the multiple forms; however, number and intensity of each form differed depending on the solid media used for growth. To determine which isoform from Bacillus sp. 12B was RSDA, the suspected isoform was purified. The optimum pH for the purified α-amylase isoform was 6.0-8.0, while the optimum temperature was 60-90°C. Isoform was considerably thermostable and Ca(2+)-independent, and actually the only α-amylase active towards raw starch. Purification and characterization of RSDA showed that not all of the solid media tested induced RSDA. From an economic point of view, it might be significant to obtain pure isoenzyme for potential use in the raw-starch hydrolysis, since it was 5 times more efficient in raw corn starch hydrolysis than the crude amylase preparation.