Effects of salt concentration on formation and dissociation of beta-lactoglobulin/pectin complexes

The formation and dissociation of beta-lactoglobulin/pectin complexes at various sodium chloride concentrations (CNaCl) have been studied by turbidimetric titration. An increase of CNaCl up to 0.1 M shifts the critical pHphi1, which designates the formation of beta-lactoglobulin/pectin coacervates, to higher pH values, whereas further increase of CNaCl from 0.1 to 0.8 M decreases pHphi1 values. These salt effects can be explained in terms of a salt-enhanced effect at lower salt concentrations or a salt-reduced effect at higher salt concentrations, respectively. On the other hand, the value of pHphi2, which corresponds to the dissociation of beta-lactoglobulin/pectin coacervates, tends to have smaller pH values when CNaCl increases from 0.1 to 0.3 M. No observable pHphi2 values are found at CNaCl higher than 0.3 M. The disappearance of pHphi2 is mainly attributed to the strong self-aggregation capability of beta-lactoglobulin at higher CNaCl. The aggregation of beta-lactoglobulin at high CNaCl is reversible, as suggested by the atomic force microscopy results.