A two-stage oxygen supply control strategy for enhancing milk-clotting enzyme production by Bacillus amyloliquefaciens

To enhance the yield and productivity of milk-clotting enzyme (MCE) by Bacillus amyloliquefaciens, a two-stage oxygen supply control strategy was proposed and successfully applied in the MCE fermentation. During the first 16 h, KLa was controlled at 72.2 h−1 to obtain high cell growth rate (v) and MCE activity (MCA) productivity (rMCA). Subsequently, KLa was controlled at 33.9 h−1 to maintain high specific MCA productivity (qMCA). Using this strategy, MCA peaked at 36 h with the MCA of 6,590.41 SU ml−1, which was 18 h earlier than other investigated processes. The concept and results described represent the basis of an industrial scale-up process to achieve high MCE yield, MCA productivity and MCA/proteolytic activity.