The role of diketopiperazines in cooked cheese flavour

Diketopiperazines are cyclic dipeptides which impart bitterness and metallic flavour. They have previously been reported at subthreshold levels in raw cheese, but not studied in cooked cheese. Four diketopiperazines (cyclo-Pro-Pro, cyclo-Val-Pro, cyclo-Ala-Pro and cyclo-Leu-Pro) were detected in seven cooked cheeses (parmesan, mozzarella, and five different cheddars). Diketopiperazines were present in substantially higher concentrations in the cooked cheeses than their raw counterparts and were above bitter and metallic thresholds in some cooked samples. Diketopiperazine formation during cooking was higher in mature cheeses than in young cheeses, suggesting that aging cheeses produces precursors to diketopiperazine formation in the raw cheese.