Heat-induced gelation of beta-lactoglobulin. 1. Time-resolved dynamic light scattering

The time evolution of the dynamics of globular protein during the gelation process via aggregation has been studied by time-resolved dynamic light sca ttering (DLS) for beta-lactoglobulin (beta-LG) in aqueous solutions at pH 2 and 7. The following facts were disclosed: (1) The scattered intensity, QT , started to fluctuate, and the intensity-time correlation function (ITCF) exhibited a power-law behavior (g((2))(tau) - 1 similar to tau(alpha-1)) at the gelation threshold, t(th). (2) The variations of [I](T)'s were differe nt between the two pHs, a gradual increase for pH 2 and a stepwise increase followed by a plateau for pH 7. (3) The exponent a was found to be strongl y dependent on pH. The values of a were 0.51 +/- 0.05 for pH 2 and 0.74 +/- 0.05 for pH 7. (4) A strong concentration and pH dependence of t(th) was a lso observed in both cases. These findings indicate that beta-LG gels forme d at pH 2 and pH 7 have different architectures, i.e., loosely tied network s (for pH 2) and fractal aggregates (for pH 7) of protein molecules.