L(+)-lactic acid production by repeated batch culture of Rhizopus oryzae in air-lift bioreactor

Abstract

l(+)-Lactic acid production using Rhizopus oryzae was investigated by varying the inoculated spore concentration in preculture medium. The spore concentration affected mycelial morphology from dispersed filamentous to pellet form. When the inoculated spore concentration was 2 × 10 6 spores/ml in flask culture, a small pellet was formed in the culture, which yielded the highest (98.2 g/ l) l(+)-lactic acid concentration after 48 h culture; when concentration was 2 × 10 5 spores/ml, clumped and compacted mycelia were observed, which caused a decrease the l(+)-lactic acid concentration (85.7 g/ l) after 48 h culture. Following in air-lift bioreactor culture, the morphology was similar to that in flask culture, and when the inoculated spore concentration was 2 × 10 6 spores/ml in the seed culture broth, the productivity of l(+)-lactic acid was 1.07 g/ l/h after 48 h culture. The pellet morphology made it possible to perform 9 cycles of repeated batch culture over 14 d. During the first 6 cycles, the average productivity was 2.02 g/ l/h, which was 1.9 fold higher than that from batch culture.