Targeted Profiling of Tryptophan- and Tyrosine-Derived Metabolites in Traditionally Fermented Foods

This study aimed to investigate the tryptophan and tyrosine-derived metabolites in traditional fermented foods. For that purpose, kynurenine, kynurenic acid, indole-3-acetic acid, indole-3-propionic acid, phenol, and p-cresol levels were analyzed using High-performance liquid chromatography (HPLC). Tryptophan metabolite levels ranged from 62.4 to 718.5 µg/100 g for kynurenine, 1.1 to 340.0 µg/100 g for kynurenic acid, 0.0 to 36.6 µg/100 g for indole-3-acetic acid, and 0.0 to 72.5 µg/100 g for indole-3-propionic acid. Tyrosine metabolite levels ranged from 4.4 to 115.7 µg/100 g for phenol and 0.0 to 7.2 µg/100 g for p-cresol. Traditional, fermented, and aged products such as tarhana appear to contain high levels of various metabolites of tryptophan metabolism. Phenol levels were also found to be high in tarhana products and aged dairy products. p-cresol levels remained generally low, with significantly high levels found only in aged cheddar cheese. These results suggest that microbial fermentation and long-term maturation may be associated with differences in the biochemical composition of the fermented foods. It is of great importance to evaluate fermented products in terms of metabolites with neuroactive and inflammatory potential.