Interaction between Chinese quince fruit proanthocyanidins and soy protein isolate: Effects on physical and oxidative stability of oil-in-water emulsions

Protein-based emulsions are extremely sensitive to droplet aggregation. The interaction between the proanthocyanidins (PAs) and protein can affect the efficacy of protein on the stability of emulsions. In this study, PAs with different molecular weights of ethyl acetate (EA) and retained aqueous (RA) phase were prepared from Chinese quince fruit and mixed with soy protein isolate (SPI) to form complexes, and their effects on the physical and oxidative stability of oil-in-water (O/W) emulsions were assessed. The results confirmed that SPI had fewer α-helices and more random coils when bound to EA and RA. The main forces between PAs and SPI were hydrogen bonds and hydrophobic interactions. Furthermore, RA-SPI, particularly EA-SPI, showed better foaming, emulsifying and antioxidant properties than SPI. The emulsifying activity index values of EA-SPI and RA-SPI were 39.7% and 33.4% higher than that of SPI, respectively. The physical and oxidative stability of O/W emulsions stabilized by SPI were lower than those stabilized by EA-SPI and RA-SPI. At day 15, the lipid hydroperoxide content of EA-SPI and RA-SPI emulsions was 30.5% and 10.3% lower than that of SPI emulsion, respectively. This study provides a basis for PAs as natural antioxidants to improve the stability of O/W emulsions.