Whey protein isolate bioactive peptide stabilised nanoemulsion

Whey protein isolate (WPI) bioactive peptide stabilised nanoemulsion.Introduction: In this study bioactive peptide fractions produced from hydrolysis of whey protein isolates (WPI) were applied as emulsifiers in nanoemulsions. Thus, the utilisation of WPI-derived bioactive peptides as emulsifiers in nanoemulsions may increase the incorporation of bioactive peptides in food systems, and lead to products with modifications to many of their macro-, micro- and nano-scale characteristics including texture and sensory attributes.Method: Peptide fractions (1–3, 3–5, 5–10 and >10kDa) were produced by ultrafiltration (UF) of crude WPI hydrolysates and were screened for their antioxidant and Angiotensin-I-converting enzyme inhibition activities. Nanoemulsions (4% oil and 96% aqueous phases) were prepared by high pressure homogenising. The peptide concentration was 2% for <10 kDa and varied from 1–4% for >10 kDa fractions. The droplet size (d), size distribution, zeta (ζ) potential during storage at 4 and 25 °C were monitored over 7 days. Results: The formation and stability of bioactive peptide-stabilised nanoemulsions depended on the peptide size, enzyme type, peptide concentration and storage temperature. The <10 kDa fractions were either poorly surface active (pepsin fractions) or weak stabilisers (chymotrypsin fractions) in nanoemulsions. The >10 kDa fractions from both enzymes formed stable nanoemulsions (d = 174.2 – 195.9 nm and ζ-potential -28.3 mV – -33.2 mV), however, this was dependent on the concentration used (1–4%) and the enzyme type. Nanoemulsions exhibited better stability when stored at lower (4 °C) than at higher (25 °C) temperatures. Conclusion: The highly bioactive <10 kDa fractions were poor stabilisers in nanoemulsions due to diminished interfacial and amphiphilic properties, but greater stability was observed for the mildly bioactive >10 kDa peptides fractions. The study demonstrated that, by using UF to control peptide size, different bioactive peptide fractions can be produced from WPI hydrolysates that are capable of forming stable nanoemulsions.