Lactic acid production by Bacillus coagulans - Kinetic studies and optimization of culture medium for batch and continuous fermentations

Bacillus coagulans is an atypical strain for lactic acid production; the th ermophile character of this strain (growth at 52 degrees C) proves that it is particularly adapted for industrial production of lactate without steril e conditions. In the first step, continuous culture was performed to define the experimen tal domain of aeration and nitrogen supplementation. The aerobic condition showed a positive influence on growth and a negative effect on lactate prod uction. At steady state for pH 6.4, the concentrations of biomass and lacti c acid Ir ere 3.9 and 19.5 g l(-1), respectively: without aeration and 4.6 and II g l(-1) with aeration. The nitrogen source is essential for the ferm entation process. Pulses of different types of yeast extract (liquid and po wder) were added into the fermentor at steady state. After pulses, biomass concentration increased two and three times with powdered yeast extract and liquid yeast extract, respectively. Liquid yeast extract,was more efficien t for growth than powdered yeast extract probably due to degradation of vit amins in a spray dryer. Secondly, a factorial fractional experimental desig n was performed to optimize batch fermentation. Temperature and pH control, the initial concentration of sugar, and the nitrogen source were optimized . For the initial sucrose concentration of 60 g l(-1), productions of bioma ss and lactic acid were 3.1 and 55 g l(-1), respectively. The maximal speci fic production rate of lactic acid is high (6.1 +/- 0.3 g/l.h/g/l cell) in comparison with mesophilic lactic acid bacteria. (C) 1998 Elsevier Science Inc.