Abstract

Lactic acid production by Rhizopus oryzae NRRL 395 immobilized in polyurethane foam was investigated by using response surface methodology. A 2³ full-factorial central composite design was chosen to explain three independent variables; glucose concentration, pH and agitation rate. The model F-value (17.01) shows that predicted model is suitable for good fitting. Linear and quadratic effects of glucose concentration and quadratic effect of agitation rate were shown to be significant for lactic acid production. Maximum lactic acid production 93.2 g/l was obtained using a glucose concentration of 150 g/l, pH 6.39 and agitation rate 147 rpm. Glucose concentration and agitation rate were found as limiting parameters. So, little variation of these parameters alters production of lactic acid. Initial pH has no effect on lactic acid production due to neutralizing agent. Production of lactic acid from immobilized whole cells which are under optimum conditions was determined about 55% that is higher than production of lactic acid from suspension culture systems.

Key words: Lactic acid, Rhizopus oryzae, immobilization, response surface methodology.