Investigation on solubility, interfacial and emulsifying properties of pumpkin (Cucurbita pepo) seed protein isolate

Abstract

Pumpkin (Cucurbita pepo) seed protein isolate (PSPI1) with protein content of 94.3 g/100 g was obtained by alkali extraction with isoelectric precipitation. Functional properties of PSPI such as solubility, interfacial and emulsifying properties were tested as a function of pH (3–8), ionic strength (μ = 0–1 mol/dm3 NaCl) and PSPI concentration. PSPI solubility had a minimum at pH 5 and reached maximal values in alkali region at pH 8. Increase in PSPI suspension concentration led to a decrease in solubility yields at pH 3 and 8, while at pH 5 solubility yield was independent of PSPI suspension concentration. Addition of NaCl caused pronounced salting–out effect at pH 3 and slight salting–in effect at pH 5 and 8. PSPI adsorption at both air/PSPI solution and oil/PSPI solution at all pH and ionic strengths tested was evidenced by an increase in surface and interfacial pressure. Nevertheless, PSPI failed to stabilize 20% oil in water emulsions at pH 5, when phase separation occurred immediately after emulsion preparation. The most stable emulsions, regardless of ionic strength, were obtained at pH 8. All emulsions were susceptible to creaming instability.