Identification of potential bioactive peptides generated by simulated gastrointestinal digestion of soybean seeds and soy milk proteins

In this work, the bioactive peptides produced during in vitro gastrointestinal digestion of soybean seeds and soy milk were investigated. The analysis was performed on extracted protein samples from soybean seeds and milk or directly on untreated soy milk. Proteins samples were subjected to simulated gastrointestinal digestion and then analyzed by nano-liquid chromatography coupled to tandem mass spectrometry for peptide sequencing. The identified peptides were 1173 in soybean seed samples, 1364 in untreated soy milk samples and 1422 in soy milk samples in which proteins were extracted by precipitation. The peptide identifications were then employed to search specific databases and look for the presence of bioactive peptides in the investigated samples, either with known biological activity or with potential antimicrobial activity. Results pointed out that soybean proteins underwent an extensive degradation process during gastrointestinal digestion and generated a large number of bioactive peptides, some with established activity, some with predicted antimicrobial activity. Finally, the supernatants collected after protein precipitation with acetone from both soybean seeds and soy milk were also analyzed to evaluate the presence of peptides produced by the action of endogenous proteases. Likely, peptides found in soy milk samples could be formed during food processing.