Use of dry yeast cells as a cheap nitrogen source for lactic acid production by thermophilic Bacillus coagulans WCP10-4

Abstract

Dry yeast cells (DYC) were used as a cheap nitrogen source to replace expensive yeast extract (YE) for L-lactic acid production by thermophilic Bacillus coagulans. Cassava starch (200 g·L–1) was converted to L-lactic acid by simultaneous saccharification and fermentation using Bacillus coagulans WCP10-4 at 50 °C in the presence of 20 g·L–1 of DYC, giving 148.1 g·L–1 of Llactic acid at 27 h with a productivity of 5.5 g·L–1·h–1 and a yield of 92%. In contrast, 154.4 g·L–1 of lactic acid was produced at 24 h with a productivity of 6.4 g·L–1·h–1 and a yield of 96% when equal amount of YE was used under the same conditions. Use of pre-autolyzed DYC at 50 °C for overnight slightly improved the lactic acid titer (154.5 g·L–1) and productivity (7.7 g·L–1·h–1) but gave the same yield (96%). Open image in new window