Evaluation of brewer's spent grain hydrolysate as a substrate for production of thermostable α-amylase by Bacillus stearothermophilus

In the present study, BSG was hydrolysed using cellulolytic enzymes and used as a growth medium supplement for cultivation of the thermophilic bacterium, Bacillus stearothermophilus in the production of α-amylase. A central composite design involving five parameters and four levels viz. starch, peptone, KCl, and MgSO₄ along with BSG hydrolysate was used to derive the optimal media composition. The fermentation was conducted using shake flasks for 36 h at a temperature of 50 °C and pH 7.0 at 220 rpm. Optimization trials revealed that maximal amylase production (198.09 U/ml) occurred with a medium composition of starch (0.2% w/v), peptone (0.2% w/v), KCl·4 H₂O (0.02% w/v), MgSO₄·7 H₂O (0.01% w/v) and hydrolysate (0.22% v/v). A 1.3-fold increase in amylase activity was obtained following novel media composition. All the factors considered in the study were found to be significant. The enzyme was purified by three step purification strategy, characterised and tested for anti-biofilm activity.