Comparative study on the novel umami-active peptides of the whole soybeans and the defatted soybeans fermented soy sauce

BACKGROUND Two kinds of soy sauce produced via fermentation of the whole soybeans and the defatted soybeans (soy sauce termed 'SSS' and 'SSD', respectively) were subjected to the treatment using aqueous ethanol solutions with high concentrations. Then tasty peptides were separated from SSS and SSD by sensory guided fractionation, using macroporous resin and reverse-phase high-performance liquid chromatography (RP-HPLC), and identified by ultra-performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry (UPLC-Q-TOF-MS/MS). Results The result showed that umami-active fractions and <= 3 kDa peptides were mainly concentrated in the supernatants resulted from the treatment with 60% ethanol and the precipitates resulted from the treatment with 80% ethanol. The contents of ammonia nitrogen, non-salt solids, bitter amino acids, amino acids in peptides and the proportion of <= 3 kDa peptides in SSS were higher than those in SSD. Sixteen and fourteen tasty peptides were separated from SSS and SSD, among them five dipeptides (gamma-Glu-Glu, Glu-Glu, gamma-Glu-Cys, gamma-Glu-Leu, Glu-Leu and Ile-Glu) with a glutamic acid residue were identified both in SSS and SSD, which have been reported as umami/kokumi-active peptides in soy sauce. Several peptides identified from SSS (Thr-Gly-Cys, Gly-Leu-Glu, Val-Glu-Ala-Leu and Gly-Gly-Gly-Glu) and SSD (Asp-Arg, Asp-Ala-Glu, Glu-Val-Cys and Gly-Gly-Gly-Glu) are tasty and/or umami-active peptides but have not been reported as tasty peptides in the past. Conclusion Most of the peptides separated from SSD and SSS could impart an umami-enhancing effect on soy sauce, and the marginally more kokumi and bitterness hydrophobic peptides were found in SSS than SSD. (c) 2020 Society of Chemical Industry

Automated summary

The study found that umami-active fractions and <= 3 kDa peptides were mainly concentrated in the supernatants resulted from the treatment with 60% ethanol and the precipitates resulted from the treatment with 80% ethanol. The contents of certain components in SSS were higher than those in SSD, and several tasty peptides were identified in both SSS and SSD, with some peptides identified in SSS and SSD not previously reported. Most of the peptides separated from SSD and SSS could enhance the umami taste of soy sauce, with slightly more kokumi and bitterness hydrophobic peptides found in SSS than SSD.