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ABSTRACT
The influence of exopolysaccharide (EPS) on the structure of whey protein (WP) molecules at different pH and ionic strengths was investigated using fluorescence and circular dichroism (CD) spectroscopy. The WPs were separated using 0.2 mol/L glacial acetic acid, which has been proved to maintain to the maximum extent the native structure of WP molecules. The interaction between WP and EPS was significantly influenced by the ionic strength and pH. The presence of NaCl reduced the repulsion and aggregation of WP at pH 7.0. The addition of EPS increased the β-sheet structure of WP and this change tends to disappear at high ionic strength (0.3 mol/L). On the other hand, the repulsive interaction between WP and EPS at pH 7.0 and 6.0 has minimal influence on tryptophan (Trp) quenching and the exposure of hydrophobic residues to the hydrophilic environment. The formation of WP/EPS complexes at pH 5.0 led to the increased exposure of the Trp group to the hydrophilic phase. Both the electrostatic repulsion and attraction increased the secondary structure of WP at all pH values tested in this research.
Funding
This work was supported by the grant of state key laboratory of dairy biotechnology, P. R. China (No. SKLDB2013-07) and Guangxi University Science Foundation for Doctor (XBZ160258).