In order to improve the production efficiency of L-phenylalanine and reduce the cost of fermentation, the dosage of FeSO4·7H2O/MnSO4·H2O was further optimized. Biotin H was no longer added, and trace elements such as pyridoxal phosphate and vitamin B2 were added. Through single factor experiment, orthogonal test and fermentor verification experiment, the key enzyme activity, L-phenylalanine yield, sugar-acid conversion rate and by-product content were taken as indexes. Finally, the types and dosage of trace elements which is suitable for L-phenylalanine fermentation were determined as follows: CaCl2·2H2O 1.1×10-2 g/L, CuSO4·5H2O 4.7×10-4 g/L,CoCl2·6H2O 6×10-3 g/L, ZnSO4 6×10-4 g/L, FeSO4·7H2O 2.8×10-2 g/L, MnSO4·H2O 1.4×10-2 g/L, NiCl2·6H2O 6.06×10-3 g/L, PLP 9.5×10-3 g/L, vitamin B2 6×10-3 g/L. The final biomass was 122.8, the yield of L-phenylalanine was 85.4 g/L, and the conversion rate of sugar and acid was 26.3%, which was 17.5%, 51.4% and 18.6% higher than that of the control group without trace elements, respectively. At the same time, the variety and production of by-products were reduced, and the key enzyme activity was improved. The final result showed that the optimized type and dosage of trace elements could increase the sugar-acid conversion rate of L-phenylalanine and improve the competitiveness of the product.
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