Heat-Induced Gelation of β-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 scattering (DLS) for β-lactoglobulin (β-LG) in aqueous solutions at pH 2 and 7. The following facts were disclosed: (1) The scattered intensity, 〈 I 〉 T, started to fluctuate, and the intensity−time correlation function (ITCF) exhibited a power-law behavior ( g (2) ( τ ) − 1 ∼ τ α-1 ) at the gelation threshold, t th . (2) The variations of 〈 I 〉 T 's were different between the two pHs, a gradual increase for pH 2 and a stepwise increase followed by a plateau for pH 7. (3) The exponent α was found to be strongly dependent on pH. The values of α 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 also observed in both cases. These findings indicate that β-LG gels formed at pH 2 and pH 7 have different architectures, i.e., loosely tied networks (for pH 2) and fractal aggregates (for pH 7) of protein molecules.