Optimization of novel hyperthermostable β amylase production by Bacillus subtilis DJ5 using solid agroresidual substrates

Abstract

Eight different low cost starchy agroresidues namely Barley (B), Wheat bran (WB), Sattu (S), Rice powder (RP), Corn flour (CF), Rice husk (RH), Yellow peas split (YPS) and arrowroot (A) were used for solid culturing of Bacillus subtilis DJ5 for production of novel hyperthermostable β amylase. Various process parameters like initial moisture content, inoculum load, medium pH and incubation temperature affecting enzyme production were optimized to ensure maximum enzyme yield. Only 10 % inoculums load and medium pH of 6.9 was found sufficient to achieve maximum enzyme production in all substrates in a decreasing order, B > WB > S > RP > CF > RH > YPS > A. Optimum β amylase production was highly dependent on initial moisture content of substrate as observed from varying requirement of moisture for different substrates. Only 50 % moisture was sufficient for maximum enzyme production of 84.29 U/gdm in CF. For B, RH, YPS, and A 60 % initial moisture resulted in higher production of 120.34, 35.19, 26.59, and 21.58 U/gdm, respectively, at 37 °C. However, for S and RP higher (70 %) moisture content allowed 113.4 and 85.56 U/gdm enzyme production, respectively. Under optimized conditions, maximum β amylase production was observed after 25 h for A, YPS, RH, RP; 41 h for B, WB, CF, and 45 h for S.