Optimization of biocatalyst specific activity for glycolic acid production

A chemoenzymatic process has been developed that employs an immobilized microbial nitrilase biocatalyst for the conversion of glycolonitrile to high-purity glycolic acid. The specific activity of this immobilized cell biocatalyst decreased significantly during initial use in either consecutive batch reactions with catalyst recycle, or in a continuous stirred-tank reactor, but the nitrilase activity remaining after this initial decrease was stable under the reactions conditions. The initial stability of this immobilized cell nitrilase catalyst has been improved by treatment of the microbial cells with glutaraldehyde prior to immobilization. Conditions for glutaraldehyde treatment were defined that completely inactivated the culture without significantly affecting nitrilase activity. A method for dehydration, storage and rehydration of the carrageenan-immobilized cells has also been demonstrated that further improves the specific activity of this biocatalyst.