Cyclic dipeptides (2,5-diketopiperazines) have been documented as occurring in an ever increasing variety of foods and natural products, such as beef, beer, cocoa, coffee, and chicken. They are a group of thermally generated compounds whose occurrence appears to be linked to Maillard reaction generated compounds. Their contribution to flavor has been reported as weak taste effects, such as bitterness and astringency. However, their presence in many cooked foods makes them difficult to ignore. Of the few sulfur containing amino acids, only one methionine-containing cyclic dipeptide has been reported previously in nature. This was cyclo-(methionine-proline) in beer and dry aged beef. This work presents the synthesis of several other cyclo-methionine analogues, their sensory attributes and their occurrence in food products, such as beef, beer and autolyzed yeast.
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