Heat induced hydrolytic cleavage of the peptide bond in dietary peptides and proteins in food processing.

We investigate the hypothesis that proteins and peptides are thermally degraded by hydrolytic bond cleavage of amide bonds, hence yielding shorter peptides as main degradation products. A series of fifteen pentapeptides with varying sequences was subjected to heating. Products were investigated by targeted UHPLC-ESI-tandem mass spectrometry and targeted analysis revealed formation of 2,5-diketopiperazines, di- and tri-peptides. Relative quantities of the thermal degradation were determined to show that hydrolytic cleavage is an important, however not dominant degradation pathway. A series of dietary intact proteins were subjected to heating and products formed analyzed by MALDI-TOF mass spectrometry. For the majority of proteins larger degradation products with m/z values between 900 and 2500 could be observed, which we tentatively assign as hydrolytic cleavage products. For coffee globulin a series of eleven short peptides formed through thermal hydrolytic cleavage could be unambiguously identified formed through thermal proteolysis. The identical products could as well be identified in samples of roasted coffee clearly illustrating the occurrence and relevance of thermally induced proteolysis of proteins.