Optimization of alpha-amylase production, immobilization and characterization by isolated Bacillus lentus under solid-state fermentation

Abstract

The agro-industrial by-product potato peels were utilized as a substrate for solid-state fermentation (SSF) using α-amylase producer (Bacillus lentus), isolated from Ain-Elseerah spring. Among twenty-eight isolates, six demonstrated clear zones of starch hydrolysis around the colonies when flooded with Gram’s iodine solution. Maximum zone of hydrolysis was of 36 mm diameter, resulting in the production of 140 U/gm DS (dry substrate) α-amylase activity in 48 h. The optimization of α-amylase production was investigated under several affecting factors, including incubation-time; temperature; pH; and also the additional carbon and nitrogen sources. The highest α-amylase activity obtained (1980.18, 1980.42, 1730.18 ,1990.16 and 1560.24 U/gm DS) was with supplementation of 2% glucose, 1% yeast extract  , After 72 h, at pH, 8 and temperature 40°C respectively. Seventy % of α-Amylase activity was retained after 1 h at 70°C and 60% activity after 1 h at 80°C. The enzyme was successfully immobilized in sodium alginate beads with immobilization yield of 7.5x10² and 10.4x10² for native and 50% enzyme respectively. Free and immobilized enzyme properties were elucidated.