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Production of L-methionine by immobilized pellets of Aspergillus oryzae in a packed bed reactor was investigated. Based on the determination of relative enzymatic activity in the immobilized pellets, the optimum pH and temperature for the resolution reaction were 8.0 and 60 °C, respectively. The effects of substrate concentration on the resolution reaction were also investigated and the kinetic constants (Km and Vm) of immobilized pellets were found to be 7.99 mmol dm−3 and 1.38 mmol dm−3 h−1, respectively. The maximum substrate concentration for the resolution reaction without inhibition was 0.2 mol dm−3. The L-methionine conversion rate reached 94% and 78% when substrate concentrations were 0.2 and 0.4 mol dm−3, respectively, at a flow rate of 7.5 cm3 h−1 using the small-scale packed bed reactor developed. The half-life of the L-aminoacylase in immobilized pellets was 70 days in continuous operation. All the results obtained in this paper exhibit a practical potential of using immobilized pellets of Aspergillus oryzae in the production of L-methionine. © 2002 Society of Chemical Industry

Aspergillus oryzae mycelium pellets with abundant aminoacylase were cultured by liquid fermentation. Mycelium pellets were immobilized by crosslinking method with reagent of gelatin and formaldehyde. Basing on the orthogonal design table L16 (4(5)), artificial neural network(ANN) model with back-propagation(BP) of error structured 4-10-15-1 was used to optimize the immobilization conditions. And the optimal conditions were obtained. Then the activity of the immobilized cells prepared under the optimal conditions was assayed. Compared with the free mycelium activity of 1800 u, the residual activity rate was 83%, which was in good accordance with that predicted by ANN. It illustrated that artificial neural network can be used to find optimal conditions for cell immobilization.

The conditions for immobilization of an l-aminoacylase-producing strain of Aspergillus oryzae in gelatin and the enzymic characteristics of the immobilized pellets were studied. The optimal concentrations of gelatin, glutaraldehyde and ethyldiamine and time of immobilization were determined. Scanning electron micrographs reveal the cross-linked structure differences between the native and immobilized pellets. Optimum pH and temperature of the native and immobilized pellets were determined. Effects of ionic strength and substrate concentration on relative activity of the native and immobilized pellets were investigated in detail. The immobilized pellets were more stable over broader temperature and pH ranges. In addition, the immobilized pellets showed stable activity under operational and storage conditions. The immobilized pellets lost about 20% of their initial activity after five cycles of reuse. The results reported in this paper show the potential for using the immobilized A. oryzae pellets to resolve d,l-methionine.