A mixed-gel of K-carrageenan and gelatin was used in L-phenylalanine production. The mixed-gel, containing 87.5% K-carrageenan and 12.5% gelatin [the total gel concentration was 4 wt%], showed the best performance and was selected for further study with Escherichia coli EP8-10. The optimum pH and temperature were 8.5 and 37 degrees C, respectively. The effects of trehalose and Mg(2+) were studied in the mixed-gel immobilization. Their optimum concentrations were 5 x 10(-2) and 2 x 10(-3) mol/L, respectively. Under the optimal conditions, 98.3% of the phenylpyruvic acid (PPA) was converted to L-phenylalanine. The activity recovery of the transaminase enzyme in the mixed-gel immobilization was higher than that in single K-carrageenan immobilization, which was 93.6%. The total PPA conversion rate was over 80% in all 15 batches, suggesting great sustainability in the mixed-gel immobilization. The maximum reaction rate (r(max)) was calculated to be 4.75 x 10(-2) mol/(Lg h). Crown Copyright (C) 2008 Published by Elsevier Ltd. All rights reserved.