Abstract: The process conditions for L-lactic acid fermentation with immobilized Rhizopus oryzae R-1 using corncob as immobilization carrier and a partial substitute for carbon source were studied. The utilization rate of corncob as a carbon source substitute and its mass ratio to glucose and optimal grinding granularity were investigated. The utilization rate of corncob by Rhizopus oryzae R-1 was 14.9%, and the optimal mass ratio between corncob and glucose was 1:4, yielding a conversion rate of glucose into L-lactic acid was 82.5%, 14.6% higher than that obtained from pure glucose fermentation. A granularity of 40 mesh was found optimal for corncob powder, resulting in an L-lactic acid yield as high as 34.68 g/L in mixed carbon source fermentation and with immobilized mycelial pellets with excellent continuous fermentation performance and a diameter ranging from 0.5 to 1.0 mm. After sixth repeated fermentation, the average conversion of glucose into L-lactic acid was 83.1%. From these result, we conclude that corncob can be a good carrier and base material for the production of lactic acid.

Key words: corn cob, Rhizopus oryzae, L-lactic acid fermentation, immobilization, mycelial pellets