6-13: Optimization of lactic acid production by pelleted-form of Rhizopus oryzae in 3 L airlift bioreactor using response surface methodology

Lactic acid production by pelleted-form Rhizopus oryzae was optimized in 3 l airlift bioreactor. The effect of pH and volumetric oxygen transfer efficiency (k_La) was evaluated according to the 2³ central composite designs. Results of regression analysis suggested linear and quadratic terms of pH and k_La were significant affected on lactic acid. Ethanol formation was found that it depends on linear and quadratic terms of pH and only linear term of k_La.  Whereas quadratic term of pH and k_La were significant affected on biomass. Interaction between pH and k_La were not influenced on considered variables. From response surface analysis, optimal pH and k_La were 5.85 and of 0.065 s^-1, respectively and lactic acid of 72.10 g/l was achieved. Subsequently, successive five repeated batches with average 77.54 g/l of lactic acid were achieved and lactic acid productivity was improved from 0.75 to 0.99 g/l h.