Optimization of protease production process using bran waste using Bacillus licheniformis

Protease enzyme production by Bacillus licheniformis bacteria was investigated. Various agricultural wastes as substrate such as wheat bran, rice bran, and sugarcane bagasse were considered. The most important effective parameters on enzyme production, like incubation time, various substrates and solid substrate particle size, media pH, different nitrogen sources in a bench-scale designed bioreactor, were optimized. The optimum protease production conditions, for both Erlenmeyer flask and batch bioreactor, at 37 °C, pH of 8, incubation time of 48h, wheat bran (5 wt%) with the particle size of 1 mm, an equal amount of peptone and yeast extract (1% w/w) and agitation rate of 180 rpm were defined. In addition, maximum protease activity in the Erlenmeyer flask and batch bioreactor was 596 and 683.93 U/mL, respectively. The pH and thermal stability of produced protease were studied; the highest amount of remaining activities at pH 8 and 60 °C were 97 and 63% of initial activities, respectively. Also, shelf-life of the produced protease enzyme retained up to 88% of its initial activity after 30 days of storage at 4 °C. However, the produced enzyme was exposed remarkably compatible with the commercial detergent; the enzyme perfectly washed and removed the stains from the sample cotton textile.