| Soy sauce has become an indispensable condiment in our daily life due to its unique color,aroma and taste.The umami taste is the main characteristic of soy sauce.It has been confirmed that umami amino acids and small molecular peptides are the main substances that constitute the umami taste of soy sauce.Studying the type and existence form of umami peptides in soy sauce is of great significance for enriching the umami mechanism of soy sauce,which can provide the theoretical basis and method guidance for the development of high quality soy sauce and new seasonings.In this paper,high-salt dilute soy sauce was used as the raw material Comparing the difference of taste between soy sauce and its artificial amino acids solution,it was found that tasty peptides had an important contribution to the taste of soy sauce Ultrafiltration and Sephadex G-15 gel chromatography were used to separate the umami fractions of soy sauce.UPLC-ESI-Q-TOF-MS/MS was used to identify the structure of the umami peptides in soy sauce.Then the taste characteristics of synthetic peptides were systematically studied.The protein materials were further screened,and the proteolytic product which was rich in the target umami peptide was prepared by two-step enzymatic hydrolysis combined with endoprotease and exoproteaseSoy sauce was divided into 4 fractions(>5000 Da,3000-5000 Da,1000-3000 Da and<1000 Da fractions)by ultrafiltration,then<1000 Da fraction was divided into 8 fractions(P1,P2,P3,P4,P5,P6,P7 and P8)by Sephadex G-15 gel chromatography.Combined with sensory evaluation analysis and amino acid composition analysis,it was found the umami intensity of P2 was higher than P1,however,the content of umami amino acids in P2 was lower than P1,and the content of peptides was higher.It indicated that the small peptides in soy sauce had an important contribution to the umami taste of soy sauce.Then P2 was identified by UPLC-ESI-Q-TOF-MS/MS,and 10 peptides were identified,namely Asn-Pro,Ala-His,Gly-Pro,Gly-Leu,Leu-Pro,Glu-Leu,Thr.-Pro,Val-Pro,Glu-Phe and Asp-Gly-Tyr,respectivelyCombined with sensory evaluation analysis and electronic tongue analysis,it was found that Asn-Pro,Ala-His,Gly-Leu and Gly-Pro had the obvious umami intensity and umami-enhancing effect.Their umami thresholds were 175 mg/L,160 mg/L,350 mg/L and 430 mg/L,and their umami-enhancing thresholds were 10 mg/L,13 mg/L,28 mg/L and 35 mg/L,respectively.The result showed that the taste characteristics of peptides were not caused by the superposition of individual amino acid;the umami peptides might not have the umami amino acid(Asp and Glu),peptides with umami amino acids did not determine umami.After the Maillard reaction of the synthetic peptides with glucose,the umami intensity and umami-enhancing effect of the synthetic peptides were significantly improvedAmong the soy protein isolate,pea protein,peanut protein,wheat protein and rice protein,the content of target umami peptide Asn-Pro and Ala-His of soy protein isolate protease hydrolysate was the highest under the enzymatic hydrolysis of neutral protease,and its umami intensity was also the highest.Among the soy protein isolate enzymatic hydrolysis of trypsin,neutral protease,alkaline protease,papain,pepsin and bromelain,the content of target umami peptide Asn-Pro and Ala-His of soy protein isolate protease hydrolysate was the highest under the enzymatic hydrolysis of neutral protease,and its umami intensity was the highest,too.After 12 hours of enzymatic hydrolysis of neutral protease,soy protein hydrolysate was continued hydrolyzed by aminopeptidase and carboxypeptidase.The result showed that the enzymatic hydrolysis effect of aminopeptidase was better than that of carboxypeptidase,and the umami score was higher.After hydrolyzed by aminopeptidase for 12 h sequentially,the contents of the target umami peptide Asn-Pro and Ala-His in the enzymatic hydrolysate were 3.32 times and 1.15 times higher than that of neutral protease only for the initial 12 h,respectively. |
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