The optical purity of L-lactic acid, RS conversion, yield and productivity were defined as follows: optical purity of L-lactic acid = {L-lactic acid (g/l)/[L-lactic acid (g/l) + D-lactic acid (g/l)]} _100%, RS conversion = {lactic acid (g/l)/[total RS containing in HR(g/l)]} _ 100%, yield = [lactic acid (g/l)/initial HR (g/l)] _ 100%, andproductivity = lactic acid (g/l)/fermentation time (h).