Chiang Mai Journal of Science

L-(+)-lactic acid production by fermentation of starchy material (low-cost agricultural products) leads to a reduction in production cost and added value of agricultural products. Rhizopus oryzae DMKU 12 was selected because it can produce the highest amount of L-(+)-lactic acid from a-amylase-treated liquefied cassava starch. L-(+)-lactic acid production by R. oryzae DMKU 12 in a shaking flask indicated that KH2PO4 and ZnSO4.7H2O significantly affected L-(+)-lactic acid production; 150 g/L of a-amylase-treated liquefied cassava starch was the concentration that maximized production. L-(+)-lactic acid of 83.7 g/L with productivity of 1.16 g/L/h was obtained by R. oryzae DMKU 12 immobilized on a 0.25 ´ 0.25 ´ 0.25 cm3 polyurethane sponge at an aeration rate of 0.75 vvm after 72 h of cultivation in a 3 L airlift fermenter. Repeated-batch culture by PUS-immobilized R. oryzae was successful at 4 cycles, with average L-(+)-lactic acid concentration and product yield of 77.7 g/L and 0.62, respectively.