Semi-continuous Fermentation Production of L-lactic Acid by Carrier-free Immobilized Rhizopus oryzae

For increasing L-lactic acid production, the inoculation amount, addition time of CaCO3, temperature, medium volume in flask, and shaking speed were optimized by single-factor and orthogonal tests, and based on medium repeated fermentation, the semi-continuous fermentation technology of Rhizopus oryzae was established in the present study. The results showed that the optimum conditions for shaking semi-continuous fermentation were as follows: inoculation amount of spore suspension 4%, inoculation amount of seed 10%, CaCO3 added at the beginning of fermentation, medium volume in flask 20% to 30%, fermented at 28 to 30 ℃ for the first 36 h and then at 32 to 34 ℃for the second 36 h, and shaking speed 200 r/min. The optimum agitation speed, aeration volume and temperature for semi-continuous fermentation in 7-L magnetic stirred fermentor were 300 r/min, 1.25 L/min and 32 ℃, respectively. Under the above conditions, the yield of L-lactic acid was up to 86%. This study is hopeful to provide some experimental basis for the industrial production of L-lactic acid using the semi-continuous fermentation technology with Rhizopus oryzae.