An investigation of the influence of pH and ionic strength on the adsorption and interfacial dilatational properties at the oil–water interface of pumpkin (Cucurbita pepo) seed protein hydrolysate

Abstract

Pumpkin (Cucurbita pepo) seed protein hydrolysate (PSPH) was obtained by enzymatic hydrolysis of pumpkin seed protein isolate using pepsin. Influence of pH (3, 5 and 8) and ionic strength, Ic (0–1 mol dm-3), on the adsorption kinetics of PSPH (diffusion rate constant, kdiff, and adsorption rate constant, kads), interfacial pressure (π) and interfacial dilatational properties (dilatational elasticity, E′, and viscosity, E″) of the oil–PSPH solution interfaces was investigated at different PSPH concentrations (c = 0.0014–14 g dm-3). It was found that PSPH adsorbs to the interface at c 0.0014 g dm-3, regardless of pH and ionic strength, as evidenced by the increase in interfacial pressure. The kdiff and kads value were found to be the highest at pH 3 and the lowest at pH 5 at the corresponding concentrations. The dilatational properties of the interfaces, which were investigated at different oscillation frequencies, ν, 0.01–0.2 Hz, showed that the E′ of the oil–PSPH solution interfaces is much higher than its E″. Moreover, E′ increases with increasing PSPH concentration at pH 5 and 8, and with increasing Ic, regardless of the pH, while E″ changes only minimally.