Protein aggregation impacts in vitro protein digestibility, peptide profiling and potential bioactive peptides of soymilk and dry-heated soybeans

Protein aggregates and in vitro digestibility of soymilk, 160 °C and 200 °C dry-heated soybeans (DHS) were investigated. The results showed that, different from the soluble protein aggregates in soymilk, thermal treatment led to formation of increased insoluble aggregates in 160 °C DHS via non-covalent bonds (hydrogen bonds and hydrophobic interactions). However, covalent bonds (protein oxidation-induced crosslinking) were predominant forces for insoluble aggregates in 200 °C DHS. The order of in vitro digestibility was 160 °C DHS > soymilk >200 °C DHS (p < 0.05). More types of peptides were identified from 160 °C DHS (2,230) than soymilk (2,104) and 200 °C DHS (2,130). Soymilk and 200 °C DHS had similar peptides distribution and sequence alignment; while 160 °C DHS generated unique peptides. Moreover, potential bioactive peptides and antimicrobial peptides were all found in the three samples. Thus, protein aggregates, caused by different cooking methods, affected protein digestibility and peptide composition.