Lactic acid production by using rhizopus oryzae

Ill SUMMARY Master Thesis LACTIC ACID PRODUCTION BY USING RHIZOPVS ORYZAE Şule BULUT University of Fırat Graduate School of Natural and Applied Science Department of Chemical Engineering 2001, Page 106 In this study, process parameters for lactic acid fermentation by Rhizopus oryzae were investigated in both shake-flasks and in a bioreactor. The effects of some fermentation conditions such as carbon source, initial pH, agitation rate and inoculum size on lactic acid fermentation were performed in shaken culture. The microorganism was used in two different forms, i.e. freely suspended and immobilised culture. In freely suspended cell system, five different carbon sources, namely glucose, sucrose, molasses, carob pod and wheat bran were used. Moreover, in some experiments, some of the carbon sources used were pre-treated with some methods like extraction, boiling, supplements etc. The effects of both type of carbon sources on lactic acid production were then compared. The effects of initial pH, agitation rate and spore inoculum size on fermentation were also studied in defined medium. In the experiments where different carbon sources were used, the values of maximum lactic acid concentrations were 59.95, 20.07, 49.28,IV 36.86 and 23.47 g/L for 150 g/L glucose, 50 g/L sucrose, 400 g/L molasses, 10 % (w/w) extracted carob pod and 50 g/L wheat bran + 50 g/L glucose, respectively. In immobilised cell system in which the microorganism was immobilised in polyurethane foam matrices, two different carbon sources, that is, glucose and molasses were selected. As in freely suspended cell system, the effects of initial pH, agitation rate and inoculum size on fermentation were conducted in defined medium with glucose. The highest concentration of lactic acid was obtained in the medium with 150 g/L glucose which was 88.75 g/L. Repeated-batch experiments were also performed in shake-flasks using immobilised R. oryzae. In these experimens, the spent medium was replaced with sterile fresh medium on various time period, i.e. 2nd, 3rd, 4th and 5th day of fermentation. The comparison of the results revealed that the best result was obtained for 2nd day replacement in which lactic acid concentration reached 51.7 g/L and levelled off almost at that value for a long period of time. In another stage of the study, lactic acid fermentation was investigated in a 1-L bench-top bioreactor using 150 g/L glucose concentration. The maximum lactic acid concentration was obtained on 216th hour of fermentation which was 103 g/L. This value was the highest lactic acid concentration obtained throughout the study which obviously indicated the scale-up was favourable for this particular fermentation. Key Woras : Lactic acid, Rhizopus oryzae, solid-state fermentation, process conditions, immobilization.