CHARACTERISTICS OF PRESSURE-INDUCED GELS OF BETA-LACTOGLOBULIN AT VARIOUS TIMES AFTER PRESSURE RELEASE

Aggregation and gelation of aqueous solutions of a beta-lactoglobulin (beta-Lg) isolate (pH 7.0; 100 to 140 g/kg protein) were induced by pr essure application and release (P-gels; 450 MPa, 25 degrees C, 15 min) , or by heating (T-gels; 87 degrees C, 45 min). Pressure-induced aggre gation led to porous gels prone to exudation in contrast to heat-induc ed gels which displayed a finely stranded network with high water rete ntion. Pore size and strand thickness were greater for P-gels than for T-gels by one or two orders of magnitude. The matrix of the strands o f P-gels consisted of highly packed particles 10 to 20 nm in diameter as estimated by SEM, suggesting a random aggregation model with equall y attractive sites per beta-Lg particles (or primary aggregates). P-ge ls displayed a lower rigidity than T-gels. Moreover, P-gels could be t otally dispersed and solubilized by homogenizing in water immediately after pressure release, Thus, pressure treatment at 450 MPa induced we aker intermolecular or interparticular forces than heating at 87 degre es C for 45 min. In contrast to T-gels, P-gels of beta-Lg underwent me chanical and protein solubility changes when stored at 4 degrees C fol lowing pressure release clearly indicating a time-dependent strengthen ing of protein-protein interactions. It appears that primary aggregate s of beta-Lg further aggregated during storage through hydrophobic int eractions and disulfide bonds. Increasing the protein concentration of the initial solutions from 100 to 140 g/kg, and therefore the probabi lity of protein-protein interactions increased pore size and strand th ickness of P-gels, with a marked trend to phase separation and protein microparticulation. Adding sucrose to the initial solutions decreased pore size and strand thickness and lessened the solid behaviour of P- gels, probably by reducing the number of protein-protein interactions induced by pressure. (C) 1998 Academic Press Limited.