Abstract:In order to determine the structural sequence of the umami peptides in soy sauce, umami peptides were isolated and identified for systematic study on their taste characteristics. Four fractions (F1, F2, F3 and F4) were obtained through membrane ultrafiltration (membrane flux: 5 ku, 3 ku and 1 ku), with F4 (< 1 ku) having the strongest umami taste based on sensory evaluation. F4 was then selected for further separation by Sephadex G-15 gel chromatography to generate eight sub-fractions (P1, P2, P3, P4, P5, P6, P7 and P8). Among which, P2 exhibited the strongest umami taste in sensory analysis. P2 was analyzed by ultra-high pressure liquid chromatography-tandem mass spectrometry. Four new umami peptides were identified through De novo sequencing. They were all dipeptides with sequences as Asn-Pro (230.1135 u), Ala-His (227.1026 u), Gly-Pro (173.0929 u) and Gly-Leu (189.1230 u), respectively. Then, four peptides were synthesized by solid-phase peptide synthesis and analyzed by sensory evaluation and electronic tongue analysis. The obtained results showed that all the four synthesized peptides had distinct umami taste or umami-enhancing effect. Further studies showed that the umami taste of soy sauce was not only derived from umami amino acids such as glutamic acid and aspartic acid, but also from certain small peptides (which were important contributors to the umami taste of soy sauce).
