Abstract

CIRCUMVENTING THE GLUCOSE REPRESSION ON INVERTASE ACTIVITY OF BAKER’S YEAST BY USING FED-BATCH FERMENTATION

Prof. Michele Vitolo*

ABSTRACT

An important subject in invertase production by baker’s yeast is overcome the repression caused by glucose present in the mash during fermentation. The aim was pursued by carrying out the fermentation in fed-batch mode. A 5L-bench fermenter containing 1.55L molasses medium was inoculated with 0.45L of inoculum (1.0g dry matter/L). The culture was carried out at 30oC, pH 5.0, 3.3mg O2/L and impeller speed of 500 min-1. Sugarcane molasses (30 g/L sucrose) was fed into the fermenter from the initial volume of 2L up to a total volume of 3.0L in both linear and exponential modes at filling time of 4h. For comparison, a batch test was carried out at the same conditions (except sucrose which all amount was added at the beginning of the fermentation). The main results showed that the catabolic repression was eliminated at glucose concentration below 0.5 g/L and the fermentation conducted in increasing linear or exponential feeding mode. Such fed-batch processes allowed to diminish the whole fermentation time by 50% in comparison with the batch process.

Keywords: Yeast, invertase, molasses, Saccharomyces cerevisiae, fed-batch fermentation.