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

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 NaCI). Solubility of PSPI was lowest at pl = 5. Solubility of both hydrolysates was higher than solubility of PSPI, especially at pH close to pl. 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 cm(3) PSPI, H1 or H2 solutions at pH 3, 5 and 8, and ionic strengths of 0 and 0.5 mol/dm(3) NaCl were prepared. Emulsifying performance of proteins depended on pH and ionic strength. PSPI failed to stabilize emulsions against droplet coalescence at pl = 5 regardless of ionic strength, and at pH 3 with 0.5 mol/dm(3) 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/dm(3)) 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. (C) 2016 Elsevier Ltd. All rights reserved.