Functional properties of pumpkin (Cucurbita pepo) seed protein isolate and hydrolysate

Abstract

Pumpkin seed protein isolate (PSPI) was enzymatically hydrolysed by pepsin to obtain pumpkin seed protein hydrolysate, PSPH. Investigation of the solubility, interfacial and emulsifying properties of both PSPI and PSPH was conducted under different conditions of pH (3-8) and ionic strength (0-1 mol dm-3 NaCl). PSPI had the lowest solubility, i.e., isoelectric point (pI) at pH 5. PSPH had higher solubility than PSPI over the whole range of tested pH and ionic strength values. The decreases in the surface and interfacial tension evidenced that both PSPI and PSPH adsorb at the air/protein solution and oil/ /protein interfaces of the solution. Emulsions (20 % oil in water) stabilized by 10 g dm-3 PSPI or PSPH solution were prepared at pH 3, 5 and 8 and ionic strength of 0 and 0.5 mol dm-3 NaCl. PSPH stabilized emulsions from coalescence at all tested pH and ionic strength values. PSPI was able to stabilize emulsions at pH 3 and 0 mol dm-3 NaCl, and at pH 8 regardless of ionic strength, while emulsions at pH 5 and both 0 and 0.5 mol dm-3 NaCl and at pH 3 when the ionic strength was increased separated into an oil and a serum layer immediately after preparation. All emulsions were susceptible to creaming instability.