Biomacromolecules, Vol.8, No.3, 992-997, 2007
Composition and rheological properties of beta-lactoglobulin/pectin coacervates: Effects of salt concentration and initial protein/polysaccharide ratio
The composition and rheological properties of beta-lactoglobulin/pectin coacervates have shown significant correlations with sodium chloride concentration (C-NaCl) and initial protein/polysaccharide ratio (r). An increase of C-NaCl from 0.01 to 0.21 M at r = 5:1 leads to the increase in both beta-lactoglobulin and pectin contents in the coacervates, which can be explained in terms of salt-enhanced effect at lower salt concentrations. Further increase of C-NaCl from 0.21 to 0.41 M decreases the proportions of these two biopolymers in the coacervates, exhibiting salt-reduced effect at higher salt concentrations. Moreover, the stronger self-aggregation of beta-lactoglobulin with increasing salt concentration gives rise to a decreasing actual protein/polysaccharide ratio in the coacervates at 0.01-0.21 M C-NaCl and r = 5:1. An increase of r from 5:1 to 40:1 often increases the actual amount of pectin chains in beta-lactoglobulin/pectin coacervates, but it exhibits a maximum in beta-lactoglobulin content at r = 20:1. A much higher storage modulus (G') than loss modulus (G'') for all beta-lactoglobulin/pectin coacervates suggests the formation of highly interconnected gel-like structure. The values of G' increase as C-NaCl increases from 0.01 to 0.21 M, whereas a further increase of C-NaCl from 0.21 to 0.41 M causes G' values to decrease to much lower values. These results further disclose the salt-enhanced effect and the salt-reduced effect at low and high salt concentrations, respectively. On the other hand, increasing r from 5:1 to 40:1 favors the formation of stronger gel-like beta-lactoglobulin/pectin coacervates, which mainly originates from the higher actual amount of pectin chains in beta-lactoglobulin/pectin coacervates at higher r values.