Abstract: In this study, malondialdehyde (MDA), a natural lipid peroxidation product, was used as an initiator to investigate the influence of MDA-induced protein structural modifications on stability and digestibility of emulsion stabilized by soy protein isolate (SPI). Results obtained showed that the contents of protein carbonyl and Schiff base significantly increased along with increasing MDA concentration, accompanied by a noticeable decrease in protein sulfhydryl content. Meanwhile, MDA promoted protein aggregation through disulfide/non-disulfide covalent bonding, where β-conglycinin (7S) was mainly involved in the latter case. O/W emulsion was further prepared with oxidatively treated SPI. It was found that MDA-induced protein oxidation had less influence on emulsion formation, but they could significantly alter the protein composition of the interface. Herein, for SPI treated with MDA at concentrations of 2.5-10 mmol/L, more 7S fractions participated in interface formation in an aggregate state. Furthermore, results from in vitro simulated gastrointestinal digestion demonstrated that emulsion digestion occurred mainly in the intestinal tract, and oxidation-induced cross-linking/aggregation of proteins could delay or reduce the replacement of bile salts at the interface, which in turn slowed emulsion digestion and decreased lipid digestibility.

Key words: soy protein isolate (SPI), malondialdehyde (MDA), protein oxidation, emulsion, simulated digestion