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

Abstract

Pumpkin seed protein isolate (PSPI) was enzymatically hydrolyzed by alcalase and pepsin to obtain H1 and H2 hydrolysates, respectively. Influence of enzymatic hydrolysis on solubility, interfacial and emulsifying properties of PSPI was investigated as a function of pH (3–8) and ionic strength (0–1 mol/dm3 NaCl). Solubility of PSPI was lowest at pI = 5. Solubility of both hydrolysates was higher than solubility of PSPI, especially at pH close to pI. Increase in ionic strength brings about salting–in or salting–out effect in PSPI, H1, and H2 solutions, depending on pH of the solutions. Tensiometric investigation showed that PSPI, H1 and H2 adsorb at both air/protein solution and oil/protein solution interfaces regardless of pH and ionic strength. 20% emulsions of sunflower oil in a continuous phase consisting of 1 g/100 cm3 PSPI, H1 or H2 solutions at pH 3, 5 and 8, and ionic strengths of 0 and 0.5 mol/dm3 NaCl were prepared. Emulsifying performance of proteins depended on pH and ionic strength. PSPI failed to stabilize emulsions against droplet coalescence at pI = 5 regardless of ionic strength, and at pH 3 with 0.5 mol/dm3 NaCl, while both hydrolysates, H1 and H2, successfully stabilized emulsions no matter of pH and ionic strength. Smallest mean droplet diameter in emulsions of increased ionic strength (0.5 mol/dm3) were obtained when they were stabilized with H2, H1, and both PSPI and H1 at pH 3, 5, and 8, respectively. All emulsions were susceptible to creaming instability.