The Purification And Identification Of Flavor Peptides From Soy Sauce And The Comparison Of Its Flavor Characteristics

Soy sauce is one of traditional femented foods in China,because of its unique color,aroma,and taste,it has become an indispensable condiment in the daily life of people all over the world.The umami of soy sauce mainly comes from nucleotides,amino acids,and peptides,therefore the study of flavor peptides in soy sauce can contribute to understand the taste compounds and guide the production of soy sauce.As one of taste-based materials,flavor peptides have delicious taste and low taste threshold,so the investigation of flavor peptides can make the type of condiments more variously and facilitate the development of new condiments and related foods.In this study,three different raw materials and production processs of soy sauce were used as experiment materials.The different concentrations of ethanol(20%,40%,60%,and 80%)were used to separate the peptides of soy sauce preliminatily.The results showed that E-1 and E-2 fractions were tasteless.E-3 fraction exhibited strong umami and kokumi.E-4 showed strong bitter and obviously kokumi.As the concentration of ethanol increased,the contents of low molecular peptides also increased.The content of peptided with molecular weight <3 kDa in E-3 fraction was more than 80%,and the content of <3 kDa peptides in E-4 was more than 90%.It indicated that ethanol classification can effectively enrich the low molecular weight peptides.The amino acids analysis showed that E-3 fraction had the highest contents of umami and hydrophilic amino acids,and the contents of bitter amino acids in E-4 were more than 50%.It indicated that abundant umami and bitter amini acids existed in these two fractios in the form of free amino acids and peptides.Therefore,we selected these two fractions to separate and purify flavor peptides respectively.The E-3 fraction and E-4 fraction were further purified by macroporous resin and iron exchange resin.E-3 fraction was divided into there compounds(M-1 fraction,M-2 fraction and M-3 fraction).The M-1 fraction exhibited strong umami and kokumi,and the contents of umani amino acids in different soy sauce(A,B,and C)were 46.3%,41.3%,and 44.4%,respectively.The low molecular weight peptides in M-1 fraction was obviously improved,and the content of <1 kDa peptides in different soy sauce(A,B,and C)were 97.41%,99.51%,and 99.47%,respectively.Through the purification of iron exchange resin,the elution fractions of E-4 exhibited stronger bitter and kokumi.The rate of desalination of elution fraction was high,and the contents of bitter amino acids in different soy sauce(A,B,and C)were 39.40%,41.6%,and 48.5%,respectively.The content of <1 kDa peptides in different soy sauce(A,B,and C)were 98.39%,98.68%,and 98.9%.The UPLC-MS/MS analysis was used to purify and identify peptides,and then all the peptides were synthetized to analyze the flavor characteristics.The UPLC-MS/MS analysis revealed 3 kinds of four peptides,23 kinds of three peptides,and 16 kinds of two peptides.The sensory evaluation results showed that peptides GGGE,KP,EF,DP,EE,DR,DA,EV,DL,VE,and GIE exhibited delicious taste and the effect ofumami-enhancement.Peptides EGV,TGC,QGI,QGL,FKE,KD,QY,HNP,NTC,GGGS,EVC,EI,VEAI,LE,ENF,GET,and SEC exhibited delicious taste and slight effect of umami-enhancement.Peptides EP,ESA,AEP,EK,EC,KGC,EVY,and AGY were tasteless.Peptides HF,HPI,LP,NAL,LCR,and SVP exhibited bitter.When these peptides were added to salt and MSG solution,their synergistic effects were significantly different.The most umami peptides had umami amino acids(Glu,Gln,Asp,and Asn),but some peptides which contained umami amino acids did not showed umami.Some low molecula weight peptides had Q value of over 1400 cal/mol but did not exhibited bitter taste.It revealed that Q rule was limited when analyzed two or three peptides.