Effects of Salt Concentration on Formation and Dissociation of β-Lactoglobulin/Pectin Complexes

Abstract

The formation and dissociation of β-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 pHφ1, which designates the formation of β-lactoglobulin/pectin coacervates, to higher pH values, whereas further increase of CNaCl from 0.1 to 0.8 M decreases pHφ1 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 pHφ2, which corresponds to the dissociation of β-lactoglobulin/pectin coacervates, tends to have smaller pH values when CNaCl increases from 0.1 to 0.3 M. No observable pHφ2 values are found at CNaCl higher than 0.3 M. The disappearance of pHφ2 is mainly attributed to the strong self-aggregation capability of β-lactoglobulin at higher CNaCl. The aggregation of β-lactoglobulin at high CNaCl is reversible, as suggested by the atomic force microscopy results