Process Optimization of Thermostable Lipase Production by Thermophilic Bacillus thuringiensis and Its Application in...

Thermostable lipases from thermophilic bacteria are highly valued for their exceptional stability and wide-ranging industrial applications. The present study aimed to maximize thermostable lipase production from thermophilic Bacillus thuringiensis via solid-state fermentation (SSF) and to evaluate its potential for bioscouring of cotton fabric. The bacterial isolate was identified based on 16S rRNA gene sequencing and cultivated using agro-industrial residues as substrates. Various process parameters, including incubation temperature and time, substrate type and concentration, inoculum form and volume, pH, carbon and nitrogen sources, oil additives, and metal ions, were optimized using a one-factor-at-a-time approach. Optimization resulted in a ~2.3-fold increase in lipase activity, with a maximum activity of 18.91 ± 0.44 U mL^-1 achieved under optimal conditions of 70 °C, 24 h incubation, 25 g sesame meal substrate, 1 mL spore inoculum, phosphate buffer (pH 8.0), 0.1 % maltose, 0.1 % sunflower oil, 0.2 % ammonium nitrate, and 0.2 % KCl. The crude enzyme was further applied for the bioscouring of desized cotton fabric as an eco-friendly alternative to conventional alkaline scouring. Lipase treatment significantly enhanced fabric hydrophilicity, yielding 85 ± 1.5 % water absorbency and a controlled weight loss of 6.2 ± 0.3 %, indicating efficient removal of hydrophobic impurities. Maximum bioscouring efficiency was achieved at an enzyme concentration of 15 U mL^-1, a 4 h incubation, and 50 °C.These findings demonstrate the strong bioscouring potential of the thermostable B. thuringiensis lipase and highlight its industrial relevance for sustainable and environmentally friendly textile processing. The optimized production strategy provides a promising platform for the large-scale application of thermostable microbial lipases in green biotechnological processes.