Acid gelation of mixed thermal aggregates of pea globulins and beta-lactoglobulin

The acid gelation by glucono-delta-lactone of thermal protein aggregates from mixed pea globulin (Glob) and beta-lactoglobulin (beta lg), namely ``mixed-aggregates'', was investigated at 25 degrees C in comparison to that of mixtures of thermal aggregates of each protein obtained beforehand separately (''mixtures of aggregates''). A phase diagram indicating thermal gelation and acid gelation conditions was obtained from mixed protein systems varying in concentration and composition. The minimum acid gelation concentration was 3% regardless of the protein aggregates system, a value about half the concentration threshold measured for thermal gelation. The rheological properties, the microstructure and the water holding capacity (WHC) of acid gels were then evaluated from 4 wt% protein aggregate solutions at different beta lg/Glob weight ratios (0/100, 30/70, 50/50, 70/30 and 100/0). Acid gelation led to weak viscoelastic gels and the gel strength increased with beta lg content. The formation of acid gel from ``mixed-aggregates'' resulted in more elastic gels and improved WHC compared to gels resulting from ``mixtures of aggregates''. This behavior seemed to correlate with the regular filamentous and highly entangled gel network structure observed for mixed-aggregates. These properties were believed to originate from the initial structure of the thermal protein aggregates strongly influenced by beta lg content.