Interfacial peptide partitioning and undiminished antioxidative and emulsifying activity of oxidatively stressed soy protein hydrolysate in an O/W emulsion

Peptides as surfactants are able to neutralize radicals, but their ability to maintain physical and chemical stability of food emulsions when oxidatively stressed is not clear. In this study, the distribution of peptides present in hydroxyl radical-stressed soy protein hydrolysate (SPH) at the interface and the inhibition of lipid oxidation in an oil-in-water (O/W) emulsion were investigated. O/W emulsions (10g/100g soybean oil, 20mg/mL protein, 1g Tween 20/100g emulsion) were prepared under 138MPa and stored for 14 days. Morphology of emulsion droplets was observed using phase contrast, confocal laser scanning, and transmission electron microscopy. The stability of all emulsions gradually decreased during storage due to flocculation but not coalescence. Oxidized nonhydrolyzed soy protein (SP) and SPH, despite 3-4-fold increases in carbonyls, retained up to 74% of their power to inhibit lipid oxidation in emulsions when compared with nonoxidized counterparts. Nonpolar peptides in SPH had a preferred adsorption at the interface while oxidation decreased the selectivity. In conclusion, oxidation that produces 4-fold carbonyl increases modifies the distribution of peptides without significantly affecting their function as emulsifiers and does not eliminate their antioxidant capacity.