Alkaline protease production by submerged fermentation in stirred tank reactor using Bacillus licheniformis NCIM-2042: Effect of aeration and agitation regimes

The effects of aeration and agitation on alkaline protease production and protease yield were studied by submerged fermentation in a batch STR using Bacillus licheniformis NCIM-2042. The agitation rate varied in the range of 200–400 rpm at each airflow rates of 1–3 vvm. The maximum protease production was found on third day (72 h) and then decreased during fourth and fifth day of operation in all batches of STR operation. The best combination of airflow and agitation rate for the present system was at 3 vvm of airflow rate and 200 rpm of agitation rate on the basis of maximum specific protease production rate. Maximum specific protease production of 102 U/mg DC was observed on third day at 3 vvm and 200 rpm. The effects of casein concentrations on protease production, viscosity changes and oxygen transfer rate were studied. The increase in casein concentration has resulted in increased viscosity of the fermentation broth with increase in time of bioreactor operation, which in turn resulted in decreased oxygen mass transfer coefficient with reduced oxygen transfer rates.