Evaluation of D ‐amino acid oxidase from Rhodotorula gracilis for the production of α‐keto acids: A reactor system

The study reports on the development of a bioreactor for the production of α‐keto acids from D,L ‐ or D ‐amino acids using Rhodotorula gracilis D ‐amino acid oxidase. D ‐Amino acid oxidase was co‐immobilized with catalase on Affi‐Gel 10 matrix, and the reactor was operated as a continuous‐stirred tank reactor (CSTR) or stirred tank with medium recycling conditions. The optimum substrate concentration and quantity of biocatalyst were determined (5 m M and 1.2 mg/L, respectively). Under optimum operating conditions, product formation was linearly related to both substrate and enzyme concentration, showing the system to be highly flexible. Under these conditions, in a stirred tank, over 90% conversion was achieved in 30 min with a maximum production of 0.23 g of pyruvic acid/day/enzyme units. Product was recovered by ion exchange chromatography. The operational stability of the reactor was high (up to 9.5 h of operation without loss of activity) and the inactivation half‐life was not reached even after 18 h or 36 bioconversion cycles. This represents the first case of a reactor developed successfully with a D ‐amino acid oxidase. © 1994 John Wiley & Sons, Inc.