(623av) Effects of Inoculation Methods On Fumaric Acid Fermentation by Rhizopus Oryzae

The production of fumaric acid from renewable resources by fungal fermentation has received much attention due to its extensive applications in polymer, medicine and food industries and the rapidly increased production cost of petroleum-based chemicals. However, current fungal fermentation process suffers from low product yield and productivity mainly due to difficulties in controlling cell morphology and mass transfer during fermentation in conventional stirred-tank bioreactors.

The production process of fumaric acid by Rhizopus oryzae involves two steps: seed culture and acid production. By using soybean meal hydrolysate as nitrogen source, cell morphology of dispersed tiny mycelia clumps was obtained in seed culture phase with enhanced fumaric acid production. However, during the inoculation process, the mycelia clumps concentration in the inoculums varies from batch to batch, causing inconsistent fermentation performance. Also, different inoculation methods, such as the inclusion of residual seed culture broth (RSCB) in the inoculums, can significantly affect the final results. Therefore, in this study, with the purpose of finding the best inoculation method for fumaric acid production, the effects of different inoculation methods and some key variables such as inoculation size were investigated. Comparing to the method in which RSCB was removed from the inoculums, the inclusion of certain amount of RSCB was beneficial for the fermentation. The relationships of the cell concentration and RSCB content in the inoculums with the fumaric acid production were also studied. Since the properties of RSCB such as the residual nitrogen content was directly related to the seed age. The effects of seed age on the fumaric acid fermentation were studied. In addition, a low pH around 2 in the final seed culture broth was observed. Since CaCO₃ is commonly used as the neutralizing agent in the fermentation medium to maintain pH ~5, NaOH was first added to adjust the pH close to 5 in order to lower the bubble production from the reactions between CaCO₃ and acids. However, fermentation results showed a negative effect of such pH adjustment and that direct addition of CaCO₃ with the sudden increase of dissolved CO­₂ concentration in the medium was favorable to the fumaric acid fermentation. By studying the effects of these inoculation methods and some key variables, it is expected to achieve a higher fumaric acid production with consistent fermentation performance.