L-Lactic acid is a promising three-carbon building-block chemical, widely used in the food, pharmaceutical, leather and textile industries and Rhizopus oryzae is an important filamentous fungus for the production of L-lactic acid with high optical purity. This study investigated the medium compositions for the maximum biomass cultivation of R. oryzae L-lactic acid fermentation, and optimized the operation parameters for semi-continuous repeated fermentation in a stirred tank fermentor using response surface method (RSM) analysis. The results indicated that a higher biomass cultivation of 3.750±0.05 g/L was achieved when the medium was composed of 12% (w/v) glucose, 0.4% (w/v) ammonium sulfate and 0.045% (w/v) monopotassium phosphate. The optimal fermentation conditions for the initial batch were as follows: the aeration was 0.75 L/(L·min), inoculation of germs was 11% and agitation speed was 560 rpm. The fermentative intensity of the initial batch and the sequentially repeated batches with self-immobilized pelletized R. oryzae were 2.162 g/(L·h) and 3.704 g/(L·h), respectively.
Key words: Self-immobilized, Rhizopus oryzae, pellet, lactic acid, response surface method (RSM).
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