Protein oxidation yields numerous modified amino acids in food, yet the microbial fate of these compounds remains largely uncharacterized. We challenged several representative food‐ and gut‐associated bacteria with oxidized methionine and tyrosine derivatives. The stability of the compounds was assessed by HPLC‐UV and HPLC‐MS/MS, whereas untargeted metabolite analysis was performed by different HPLC‐MS coupling techniques. While degradation of oxidized tyrosine was highly strain‐specific—yielding novel α‐hydroxy and α‐keto acids primarily in pseudomonads—methionine derivatives were universally depleted. Detailed metabolic profiling pointed to a novel capability regarding methionine handling: Enterobacter cloacae —in contrast to related species—produced methionine from methionine sulfone (MetSO 2 ), providing the first evidence of bacterial methionine sulfone reduction. Moreover, common food microbes actively convert oxidized methionine and tyrosine derivatives to previously unknown metabolites, which serves as a starting point for research on the influence of oxidized amino acids in food on flavor development during fermentation and on their role during microbial metabolization in the human gut.
Behringer et al. (Thu,) studied this question.