Gelation of hydrolysates of a whey protein isolate induced by heat, protease, salts and acid

Hydrolysis of a whey protein isolate solution (21%) by a protease from Bacillus licheniformis (BLP) resulted in protein aggregation (45°C, pH 7.0). The aggregation was monitored by spectrophotometry, dynamic light scattering, and electron microscopy. Additions of CaCl₂ (40 mM), NaCl (200 mM) or glucono-delta-lactone (GDL, pH 5.0) to the turbid hydrolysates led to rapid gelation. Heating (80°C, 30 min) or further BLP (1% enzyme: substrate ratio) treatment also gelled the hydrolysates. The hardness of the gels varied with the size of the aggregates (66-490 nm). The heat-induced gel showed the highest hardness and adhesiveness, but the lowest cohesiveness (p < 0.05). The salt-induced gels were the most cohesive (P < 0.05). The heat-, GDL, and BLP-induced gels were microstructurally composed of irregular aggregates similar in shape and size (~200 nm) to those in the parent hydrolysate, while the micrographs of salt-induced gels showed larger (~300 nm) and regular aggregates.