Stability of whey protein bioactive peptide-stabilised nanoemulsions: effect of pH, ions, heating and freeze–thawing

Whey protein hydrolysates are important food emulsifiers and bioactive ingredients. This study investigated the stability of whey protein isolate (WPI) bioactive peptide fraction nanoemulsions under representative food processing and storage conditions: pH (3–9), ion concentration (Na+, 0–200 mm and Ca2+, 0–15 mm), thermal treatment (30–90 °C) and freeze–thawing. Bioactive peptide fractions, UC–10 and UP–10, were obtained by ultrafiltration of chymotrypsin or pepsin WPI hydrolysates, respectively. The nanoemulsions produced with these fractions had droplet diameters of 177 ± 3.5 nm (UC–10) and 154 ± 1.6 nm (UP–10). Nanoemulsions destabilised at pH 3–5, around the isoelectric point of WPI proteins but were stable at higher pH values, 6–9. Nanoemulsion instability escalated above critical Na+ (25 mm) and Ca2+ (2.5 mm) concentrations, but Ca2+ accelerated droplet aggregation more strongly than Na+. Furthermore, nanoemulsions were moderately stable to heating and freeze–thawing. Overall, both WPI bioactive peptide-stabilised nanoemulsions showed consistent stability to the processing conditions. This study expands on designing, producing and utilising nanoemulsions based on WPI bioactive peptides.