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 degrees 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 degrees 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 (similar to 200 nm) to those in the parent hydrolysate, while the micrographs of salt-induced gels showed larger (similar to 300 nm) and regular aggregates. (C) 1998 Elsevier Science Ltd. All rights reserved.