Center for Crops Utilization Research

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Fermentation Production of Organic Acids

Overview

Each year the cost-ratio of a bushel of corn to a barrel of crude oil makes corn increasingly competitive. Fermentation can reduce the cost of producing many valuable industrial chemicals now derived from petroleum. When the raw material for these reactions is cornstarch, a renewable resource is being used. In addition, increased use of corn for industrial products strengthens and diversifies the national agricultural economy. Several CCUR research teams are developing novel fermentation and product-recovery technologies.

One group of researchers is studying the production of propionic acid from corn. Currently, propionic acid, a mold inhibitor, is industrially synthesized from petroleum. The research team is developing an economical process that uses genetically improved fermentation bacteria to maximize product yield. In the past, industrial fermentation techniques have been impeded by the very products they produce. As the level of microorganism-produced acid or alcohol increases, it interferes with the growth and metabolism of the organisms, eventually killing them. The team has developed a unique approach to product recovery that uses a specialized membrane to selectively remove the acid without disturbing the culture. This should allow industrial manufacturers to continuously produce acid while maintaining the culture's viability. Membrane recovery techniques of this type may allow chemical producers to develop fermentation technologies previously deemed too costly or energy intensive because of the associated separation costs.

Other researchers are developing the technology to produce lactic acid by fermentation. Corn-derived lactic acid is a valuable chemical feedstock. It is used in the production of acetic, acrylic, and propionic acids, and can be used to manufacture polyester, resulting in a biodegradable plastic derived from a natural and renewable source. The work centers on increasing fermenter efficiency by developing strains of lactic acid bacteria that produce more acid and are more resistant to the higher-acid broth concentrations associated with membrane-recovery processing systems.

The researchers also have developed a specialized bioreactor to produce and recover lactic acid from cornstarch. High-purity lactic acid is a must for the production of plastic polymers. The new bioreactor uses bacteria that are fixed to chips arranged in a bed or column. The feed substrate can then be passed through the chips; the out-flow contains the lactic acid produced by the microorganisms. This process is advantageous in that the broth and resulting acid are relatively free of dead bacteria and similar unwanted by-products usually present in conventional fermentation broths. Recovery of the acid employs a technique known as ion recovery. Existing ion-recovery techniques are high-temperature, energy intensive processes. The new process will operate at lower temperatures and with fewer intermediary chemicals. Contact the ISU Fermentation Facility for service and capability information.