Effect of pH, aeration and sucrose feeding on the invertase activity of intact S. cerevisiae cells grown in sugarcane blackstrap molasses

Abstract

S. cerevisiae was grown in a blackstrap molasses containing medium in batch and fed-batch cultures. The following parameters were varied: pH (from 4.0 to 6.5), dissolved oxygen (DO) (from 0 to 5.0 mg O2L-1) and sucrose feeding rate. When glucose concentration (S) was higher than 0.5 g L-1 a reduction in the specific invertase activity of intact cells (v) and an oscillatory behavior of v values during fermentation were observed. Both the invertase reduction and the oscillatory behavior of v values could be related to the glucose inhibitory effect on invertase biosynthesis. The best culture conditions for attaining S. cerevisiae cells suitable for invertase production were: temperature=30°C; pH=5.0; DO=3.3 mg O2L-1; (S)=0.5 g L-1 and sucrose added into the fermenter according to the equations: (V-Vo)=t2/16 or (V-Vo)=(Vf-Vo)·(e0.6t-1)/10. © 1995 Society for Industrial Microbiology.