The Influence of Enzymatic Hydrolysis on Adsorption and Interfacial Dilatational Properties of Pumpkin (Cucurbita pepo) Seed Protein Isolate

Abstract

Pumpkin seed protein isolate, PSPI, was enzymatically hydrolysed by alcalase to obtain pumpkin seed protein hydrolysate, PSPH. Kinetics of PSPI and PSPH adsorption layer formation at oil–protein solution interface and interfacial dilatational properties of the layers were investigated by the drop profile analysis tensiometer (PAT) in order to determine the influence of enzimatic hydrolysis on the interfacial properties of pumpkin seed proteins. The properties were investigated at different protein solution concentrations (0.0008–0.8 g/100 mL), ionic strengths (0–0.5 mol/L NaCl), and at two acidic pH (3 and 5, where PSPI’s pI = 5). It was found that both, PSPI and PSPH, contribute to an increase in the interfacial pressure, π, at the oil–protein solution interface and form the interfacial proteinaceous films. Dilatational elasticity, E’, of the interfacial films was found to be a few times higher than the dilatational viscosity, E”, regardless of the experimental conditions. The obtained diffusion rate and adsorption rate constants, kdiff and kads respectively, were higher for PSPH than for PSPI. kdiff was found to increase as protein concentration was increased, and to decrease as ionic strength was increased, for both PSPI and PSPH. At pI = 5, PSPH showed an increased π and E’, as well as mitigated influence of ionic strength on kads when compared to PSPI.