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The behaviour of β-lactoglobulin (β-lg)-stabilized emulsions (1.0wt% protein and 20.0wt% soy oil) using pepsin digestion under simulated gastric conditions (37°C, pH 1.2 and 34mM NaCl ionic strength, with continuous shaking at approximately 95rev/min for 2h) 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±0.5mV to +17.6±1.2mV 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 …