Em. Dumay et al., CHARACTERISTICS OF PRESSURE-INDUCED GELS OF BETA-LACTOGLOBULIN AT VARIOUS TIMES AFTER PRESSURE RELEASE, Lebensmittel-Wissenschaft + Technologie, 31(1), 1998, pp. 10-19
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.