Behaviour of an oil-in-water emulsion stabilized by β-lactoglobulin in an in vitro gastric model

The behaviour of β-lactoglobulin (β-lg)-stabilized emulsions (1.0 wt% protein and 20.0 wt% soy oil) using pepsin digestion under simulated gastric conditions (37 °C, pH 1.2 and 34 mM NaCl ionic strength, with continuous shaking at approximately 95 rev/min for 2 h) was investigated. Changes in particle size, ζ-potential and microstructure were monitored as a function of incubation time in the gastric fluid. Initially, β-lg formed a stable anionic emulsion at pH 7, but the emulsion underwent extensive droplet flocculation, with some coalescence, on mixing with the simulated gastric fluid. The ζ-potential values gradually changed from −57.1 ± 0.5 mV to +17.6 ± 1.2 mV because of pH change and peptic hydrolysis of the interfacial layer. Native β-lg was largely resistant to pepsin attack but, when β-lg was present at the interfacial layer of the oil-in-water emulsion, it was rapidly hydrolysed by pepsin, as shown by sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The droplet flocculation and the coalescence observed during hydrolysis were markedly dependent on the digestion time.