Properties of Gels Induced by Heat, Protease, Calcium Salt, and Acidulant from Calcium Ion-Aggregated Whey Protein Isolate

Gelation that was induced by heat, protease, calcium salt, or acidulant from a solution of Ca²⁺-aggregated whey protein was investigated by analyses of the rheological, textural, and microstructural properties of the gel. The addition of 40 mM CaCl₂ to 18% whey protein solution resulted in aggregation during 4 h of incubation at 45°C. The occurrence of aggregation was determined as increases in turbidity and in mean aggregate size. Hydrolysis by a protease from Bacillus licheniformis (1% enzyme to protein, wt/wt), a decline in pH by glucono-δ-lactone (1.5%, wt/vol), an increase in ionic strength with CaCl₂ (60 mM), or heat treatment (80°C for 30 min) all led to gelation of the aggregated whey protein solutions within 40 min. The gels formed differed widely in texture and rheological properties. The heat-induced gel was over 20 times stronger than the gels that were induced by protease from Bacillus licheniformis, glucono-δ-lactone, and CaCl₂. The heat-induced gel also showed significantly highest adhesiveness. The gels induced by CaCl₂ and glucono-δ-lactone had significantly higher cohesiveness than the gels induced by heat or enzyme. The micrograph of the aggregated whey protein solution showed loose, irregular aggregates, which were reflected in gels induced by CaCl₂ or glucono-δ-lactone. The aggregates in the gels that were induced by heat or enzyme were larger than the parent aggregates. This difference may be due to fusion or to further aggregation of the parent aggregates during the inducement of gelation.