3.2. The effects of temperature, pH, carbon source, and nitrogen source
on LA production
Moderate thermophilic B. coagulans strains have been recently
used for high-yield LA production. In this study, we first examined
the effect of temperature on B. coagulans LA204 LA fermentation in
both glucose and xylose media. As shown in Fig. 2, the highest LA
yields (0.89 and 0.88 g/g sugar) were reached at 50 C in both
media; while lower yields were obtained at other temperatures.
Higher levels of acetic acid were produced in the xylose medium
(0.07–0.12 g/g sugar) than in glucose medium (0.04–0.05 g/g sugar)
at various temperatures. The effect of initial pH values on LA
fermentation was also examined and the results indicate that an
initial pH of 6.0 is optimal for lactic acid fermentation by this
strain.