Emulsification performance and interfacial properties of enzymically hydrolyzed peanut protein isolate pretreated by extrusion cooking

In this study, peanut protein isolate (PPI) was modified with extrusion pretreatment and papain-induced proteolysis. SDS-polyacrylamide gel electrophoresis showed that extrusion pretreatment conducted at 130 °C substantially increased the protease accessibilities of the major constitutive proteins (conarachin and arachin) in EPPI (extrudates of PPI), resulting in a remarkable increase in the degree of hydrolysis (DH) and protein solubility for the hydrolysates. Analysis of droplet size distributions and microstructures of oil-in-water model emulsions formed by PPIH (PPI hydrolysates) and EPPIH (EPPI hydrolysates) with different DH showed that extrusion pretreatment led to a marked enhancement in the emulsification performance for the hydrolysates. EPPIH (6.2% DH) was capable of producing a stable emulsion (20 vol% sunflower seed oil) with fine droplets (d32 = 0.4 μm, d43 = 1.6 μm) at 2.5% (w/v) sample content, whilst the equivalent emulsions made with control PPI and PPIH (0.9% DH) required 6.5% and 5.5% (w/v) level of sample, respectively. Based on investigations of surface pressure versus sample concentration profiles and saturation surface Loads (Γsat) for some selected PPIH and EPPIH, it was found that with most insoluble protein particles in EPPIH being enzymically hydrolyzed and becoming soluble, the production of surface active peptides with low Γsat was substantially promoted during enzymic proteolysis, which was responsible for the efficient use of EPPIH (6.2% DH) on generating and stabilizing small emulsion droplets against bridging flocculation during homogenization. These results indicated that hydrolyzed PPI could be used an efficient food emulsifying agent with extrusion pretreatment substantially increasing its protease accessibility.