Study on the synthesis and application of homogentisic acid in tocopherol enrichment through Monascus purpureus fermentation

Homogentisic acid (HGA), a product of the L-tyrosine metabolic pathway, serves as a substrate for tocopherol synthesis. Previous studies revealed that the fermentation of coix seeds by M . purpureus could simultaneously upregulate tocopherol and HGA levels. Therefore, this study focused on HGA to investigate its specific effect on tocopherol production during the fermentation process. The results showed that 0.02% Exo-HGA significantly increased tocopherol yield by 53.11%, reaching 184.808 μg/g. Based on the seed culture medium, the optimal formulation of key factors for promoting End-HGA synthesis in M. purpureus was determined. It was obtained through single-factor experiments and uniform design: D-fructose (36.816 g/L), L-tyrosine (0.656%), yeast extract powder (7 g/L), ZnSO 4 (0.654 g/L). Under these conditions, M. purpureus exhibited good growth, with an End-HGA yield reaching 844.461 μg/mL. In addition, fermentation of coix seeds with End-HGA led to an increase in the total tocopherol yield by 57.36%, reaching 181.303 μg/g. This result was comparable to that achieved with Exo-HGA addition. Therefore, enhancing End-HGA synthesis is an effective strategy to achieve a high tocopherol yield through M. purpureus fermentation. In conclusion, this study demonstrated that the regulation of microorganisms can enable high-level synthesis of target products and improve the efficiency of deep conversion and utilization of plant substrates.