| Peptides abundant in food and protein hydrolysates have known to be important to both unprocessed and processed flavors. In this study, the effect of peptide chain length on flavor formation was investigated using glycine, diglycine, and triglycine as precursors in the reaction of glucose (glc). The experiments were conducted at 160°C for 1 hour in both aqueous and non-aqueous solutions. Volatile compounds were identified and quantified by stir bar sorptive extraction-gas chromatography-mass spectrometry, and nonvolatile compounds were characterized and quantified by high-performance liquid chromatography-tandem mass spectrometry. The amount of volatile generation increased as water decreased, and the overall reactivity of the glycine and its peptides in volatile formation was glycine ≥ triglycine > diglycine. Susceptibility of peptide bond was suggested to be one of the main factors for volatile formation. Triglycine was unstable and mainly degraded into cyclic (Gly-Gly) and glycine, whereas diglycine had a higher stability than triglycine toward hydrolytic cleavage of the peptide bond. The formation of cyclic (Gly-Gly) was not significantly affected by water content and addition of sugar, but greatly affected by heating time.; The effect of neighboring amino acids and sequence in peptides on flavor profile was investigated using cysteine-containing peptides, gamma-glutamyl-cysteine-glycine (glutathione, GSH), gamma-glutamyl-cysteine, cys-gly and gly-cys as precursors in the reaction with glc at pH 5.5. Sulfur containing volatiles such as thiophenes, thiazoles and cyclic polysulfides were the major volatile compounds formed in the reaction model system. Volatiles were generated more in gamma-glu-cys/glc reaction than in gly-cys/glc and more in GSH/glc than in cys-gly/glc which suggests that the glutamyl group in front of cysteine can significantly increase the formation of sulfur-containing compounds. The results were also in accordance with the overall odor profile in which the sulfury note was enhanced in gamma-glu-cys/glc reaction mixture. The sequence order in peptide (cys-gly and gly-cys) influenced not only the volatile formation, but also dramatically on the taste sensation. |
