Simultaneous saccharification and fermentation of potato starch wastewater to lactic acid by Rhizopus oryzae and Rhizopus arrhizus

The biochemical kinetic of simultaneous saccharification and fermentation (SSF) for lactic acid production by fungal species of Rhizopus arrhizus 36017 and Rhizopus oryzae 2062 was studied with respect to growth pH, temperature and substrate. Both R. arrhizus 36017 and R. oryzae 2062 had a capacity to carry out a single stage SSF process for lactic acid production from potato starch wastewater. The kinetic characteristics, termed as starch hydrolysis, accumulation of reducing sugars, lactic acid production and fungal biomass formation, were affected with variations in pH, temperature, and starch source and concentration. A growth condition with starch concentration approximately 20 g/l at pH 6.0 and 30 °C was favourable for both starch saccharification and lactic acid fermentation, resulting in lactic acid yield of 0.85–0.92 g/g associated with 1.5–3.5 g/l fungal biomass produced in 36–48 h fermentation. R. arrhizus 36017 had a higher capacity to produce lactic acid, while R. oryzae 2062 produced more fungal biomass under similar conditions.