Analysis of sequence composition characteristics and peptide mining of soy protein isolate

In this study, the sequence composition of soybean protein isolate (SPI) was identified by proteomics combined with sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) analysis. The bioactive and umami peptides were mined by high-abundance peptide sequences in SPI based on peptitomics analysis, and in combination with the peptide database and prediction model. The results indicated that SPI was mainly composed of 8 protein sequences, among which the sequences P11827, P0DO16, and P25974 corresponding to the α, α', and β subunits in β-conglycinin, respectively, accounting for 42.49%. The sequences P04776, P04005, P11828, P04347, and P02858 were derived from the 5 subunits (G1 to G5) in glycinin, accounting for 57.51%. It was statistically found that the relative contents of dipeptides such as glutamine-glutamic acid (EE), glutamine-glutamyl (QQ), and aspartic amine-glutamic acid (DE) in the SPI sequence were relatively high, which were 3.74%, 3.07%, and 2.84%, respectively. The repeat features of dipeptide starting and ending with E or Q in the corresponding sequence were prominent, with theoretical maximum contents all greater than 16%, and they had high potential umami characteristics or hypoglycemic activities, fully demonstrating the wide application prospects of SPI in functional umami agents.