Enhancing the efficiency of L-tyrosine by repeated batch fermentation.

L-tyrosine is a widely used aromatic amino acid with an increasing market demand. Improving the parameters of L-tyrosine production results in a more cost-effective process that is of great interest for industrial applications. GHLTYR-168 was used to ferment L-tyrosine, with a productivity of 1.73 g/(L·h) and a yield of 17.6%. To further increase its production efficiency, repeated batch fermentation was applied to L-tyrosine, in which both replacement time points and ratios were studied during different fermentations. The broth substitution time point had no significant effect on L-tyrosine subjected to repeated batch fermentation, and 70% broth replacement ratio was the best choice. Repeated batch fermentation was performed in 5 batches within 100 h, among which the efficiency of the third batch fermentation was the highest. In the third batch fermentation, the productivity and yield were 2.53 g/(L·h) and 30.1%, respectively. Compared with that during fed-batch fermentation, the productivity and yield of L-tyrosine increased by 43.8% and 74.0%, respectively, during repeated batch fermentation. This is the highest level of L-tyrosine fermentation reported so far. Thus, repeated batch fermentation of L-tyrosine can improve its production efficiency.