Production of alkaline protease by a thermophilic Bacillus subtilis under solid-state fermentation (SSF) condition using Imperata cylindrica grass and potato peel as low-cost medium: Characterization and application of enzyme in detergent formulation

Among the different agro-industrial waste products and kitchen waste materials, viz. mustered oil cake, wheat bran, rice bran, Imperata cylindrica grass, banana leaves, potato peels and used tea leaves screened as substrates/solid supports for the production of alkaline protease by a thermophilic strain of Bacillus subtilis DM-04 under solid-state fermentation, potato peel followed by I. cylindrica grass supported maximum protease production. Further, potato peel and I. cylindrica grass mixed in a ratio of 1:1 (w/w) significantly (P < 0.05) enhanced the protease production by B. subtilis DM-04 compared to individual substrate. Among the tested nitrogen compounds, 0.1% (w/w) beef extract followed by yeast extract served as the best co-nitrogen sources for protease production by B. subtilis DM-04 strain on I. cyindrica grass. Distilled water adjusted to pH 8.0 was most efficient moistening agent for protease production. The crude protease displayed optimum activity at 37–45 °C temperature range and showed characteristics pH optima at pH 8.0–9.0. The protease from B. subtilis DM-04 retained 67% of its original activity post-heating at 60 °C for 15 min. Among the tested protein substrates, casein served as the most preferred substrate for the enzyme. Crude protease exhibited a significant stability and compatibility with most of the tested commercial laundry detergents, demonstrating its feasibility for inclusion in laundry detergent formulation.