Reducing by-product formation in L-lactic acid fermentation by Rhizopus oryzae.

During L-lactic acid fermentation by Rhizopus oryzae, increasing the phosphate level in the fermentation medium from 0.1 g l(-1) to 0.6 g l(-1) KH2PO4 reduced the maximal concentration of L-lactic acid and fumaric acid from 85 g l(-1) to 71 g l(-1) and from 1.36 g l(-1) to 0.18 g l(-1), respectively; and it decreased the fermentation time from 72 h to 52 h. Phosphate at 0.40 g l(-1) KH2PO4 was suitable for both minimizing fumaric acid accumulation and benefiting L-lactic acid production.