Fumaric acid fermentation by Rhizopus oryzae in submerged systems
Abstract
Fumaric acid has broad industrial applications, e.g. in the food industry, the paper industry and the polymer industry. Fumaric acid can be produced by fungal fermentation by Rhizopus oryzae from glucose. Growth morphology of fungi can vary from a filamentous form to a discrete pellet form depending on a number of factors such as the medium components, the size of inoculum, and the physical environment. Success in forming pellets of small size is very important in industrial applications of fungal fermentation. In this work, initial pH and trace metal ions in cultivation media affecting growth morphology of this fungus were studied to obtain useful skills in preparing fungal pellets of small size (<1mm in>diameter). It was observed that the presence of acid in cultivation media is inhibitory to fungal growth, and fast growth is noticed to promote the formation of pellets of large size or filamentous forms. Further, an efficient process for production of fumaric acid from glucose by R. oryzae was successfully developed. Fumaric acid fermentations in a 10-L bubble column fermentor using different neutralizing agents were investigated. Experiments indicate that using limestone as the neutralizing agent, the highest fumaric acid weight yield and volumetric productivity are obtained, 82.4% and 1.20g/L/hr, respectively. Using NaHCO 3 as the neutralizing agent does not give a higher fumaric acid weight yield, but has advantages of simplifying downstream process and reuse of cells. A novel process of simultaneous fermentation and separation for fumaric acid production was successfully investigated. An anion-exchange resin column was coupled with a 2-L stirred tank fermentor to remove fumaric acid produced. With this process a 66.8% fumaric acid weight yield and 1.09 g/L/hr volumetric productivity can be obtained. Another success in this work is acquiring a generic method for recovering and recycle of weak acids. This novel method can be directly applied to recovery of fumaric acid produced from the process of fumaric acid fermentation coupled with an ion-exchange resin column. It can successfully isolate fumaric acid at the expense of heat, and avoid using mineral acids and alkalis to produce a large amount of waste salts.
Degree
Ph.D.
Advisors
Tsao, Purdue University.
Subject Area
Agricultural engineering
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