Safe Production Of Umami Peptides And Their Function Analysis

Peptides are crucial for the mild, delicious umami taste characteristics of traditional tasty food in China, such as chicken soup, soy sauce, douchi, etc. Whereas the mechanism remains unclear. This makes the traditional umami seasonings containing predominant peptides difficult to be produced in large-scale and low cost. The relativity between flavour and peptide sequences as well as amino acid contents of chicken soup was studied. Based on this theory, soy protein was hydrolyzed by neutral protease and flavourzyme and the enzymolysis condition were optimized. Amino acid contents and peptide sequences of the optimized soy protein hydrolysates was analyzed. Novel tender, harmonious and nutritional umami soy protein hydrolysate food additives are generally prepared, and they are promising for substituting for simple constituent umumi condiments such as monosodium glutamate(MSG), flavor nucleotides, chicken extracts, etc.The free and total amino acid contents of chicken soup were analyzed by amino acid analyser. Of free amino acids, umami and sweet amino acid contents were significant higher than strong hydrophobic amino acid which elicits the bitter taste. The high proportion of sweet and umami amino acids are responsible for the umami taste of the chicken soup. Peptides in the fraction <3000 Da using ultrafiltration was studied, and 786 peptides were obtained and analyzed by high performance liquid chromatography-mass spectrometry(HPLC-MS). Of these peptides, there are high proportion of umami and sweet amino acid residues and low of hydrophobic amino acid residues. Hydrophobic amino acid residues seldom located in the C terminus. Peptide bonds with hydrophilic amino acids in primary structure were preferentially cleaved in the thermo-process.Based on the relativity between umumi flavour and peptide sequences in chicken soup,soy protein isolates(SPI) were selected as the material for the chicken soup-like umumi food additive preparation because of their high productivity, low cost, high umami and sweet amino acid residue ratio, and chelestorol-free. SPI was heated for 15 min in 100 ℃ at pH 7, and LAL content was found to be 540 mg/kg protein which was lower than the standard of infant formula. The enzyme ratio between neutral protease and flavourzyme was 4:6. Amino acid contents and sequences of peptide fractions <3000 Da in protein hydrolysates after 12 h was analyzed, there are high ratio of umami and sweet amino acid residues. Soy peptides influencing the ACE activity was detected. Higher HD of proteinhydrolysates could more effectively inhibit the activity of ACE.Protein were enzymatically hydrolzed under aseptic condition in order to improve enzymatic hydrolyzation time, then the HD of protein hydrolysates could reach up to 35%after 24 h. The soy protein hydrolyzed peptides contained high ratio of umami and sweet amino acid residues which were similar to peptide composition of chicken soup.