Fermentation optimization of rennet-producing Bacillus amyloliquefaciens GSBa-1 for high-density culture and its kinetic model

Abstract

The milk-clotting enzyme (MCE) produced by Bacillus amyloliquefaciens GSBa-1 achieved the scale-up criterion from 0.25-L erlenmeyer flask to 5-L bioreactor sucessfully and exhibited remarkable milk-clotting activity (MCA) (626.3 SU/mL) that was 1.45-fold higher than the control by optimizing both medium composition and fermentation conditions.The growth of GSBa-1 was optimized through response surface methodology employing Plackett-Burman design and Box-Behnken design. The final optimized fermentation conditions were as follows: maltose (7.258g/L), corn steep liquor (8.15g/L), and Tween 80 (1.97) g/L; constant fermentation pH (7.0), temperature (45 °C) and stirrer speed (200 rpm). Kinetic models of microbial growth (X), product formation (P), and substrate consumption (S) were constructed, respectively. The derived model was the first reported model for GSBa-1 rennet production, contributing visual description for the rennet fermentation process, as well as the improvement of its productivity and efficiency.