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 degr ees C, pH 7.0). The aggregation was monitored by spectrophotometry, dy namic light scattering, and electron microscopy. Additions of CaCl2 (4 0 mM), NaCl (200 mM) or glucono-delta-lactone (GDL, pH 5.0) to the tur bid 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 ag gregates (66-490 nm). The heat-induced gel showed the highest hardness and adhesiveness, but the lowest cohesiveness (P < 0.05). The salt-in duced 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 h ydrolysate, while the micrographs of salt-induced gels showed larger ( similar to 300 nm) and regular aggregates. (C) 1998 Elsevier Science L td. All rights reserved.