Evaluation of fungal lactic acid accumulation using glycerol as the sole carbon source

This study investigated the glycerol utilization for lactic acid accumulation by the filamentous fungus Rhizopus oryzae 9363 and compared it with the conventional carbon source glucose. No lactic acid accumulated in the glycerol media at 30°C, in contrast to the glucose media. Increasing the temperature from 30 to 37°C led to a 63% decrease in the average growth rate of R. oryzae in glycerol media and a 61% increase in the average cell mass yield, and the cultures on glycerol media at 37°C were able to generate 0.6 g/L lactic acid. While, raising temperature significantly inhibited lactic acid production on glucose media. Moreover, supplementing cultures with sodium pyruvate significantly improved the lactic acid synthesis of R. oryzae on glycerol media, with lactic acid concentrations reaching 1.33 g/L at 37°C and 0.67 g/L at 30°C, respectively. Our results indicate that glycerol utilization for lactic acid accumulation by Rhizopus sp. is limited by the availability of intracellular pyruvate, and controlling pyruvate flow is a key to enhancing the lactic acid accumulation.