Modification of whey protein concentrate hydrophobicity by high hydrostatic pressure

The objective of this study was to evaluate the influence of high hydrostatic pressure (HHP) treatments on hydrophobicity of whey protein concentrate (WPC). An increase in binding affinity or decrease in apparent dissociation constant indicates increased hydrophobicity, which is positively correlated with functional properties. The effects of HHP treatment (600 MPa, 50 degrees C, 0 to 30 min) on intrinsic fluorescence of WPC and the binding properties of WPC for aromatic 1-anilino-naphthalene-8-sulfonate (ANS) and aliphatic cis-parinaric acid (CPA) probes were studied. HHP treatment of WPC resulted in an increase in intrinsic tryptophan fluorescence intensity and a 4 nm red shift after 30 min of treatment, which indicated changes in the polarity of tryptophan residues microenvironment of whey proteins from a less polar to a more polar environment. There was an increase in the number of binding sites of WPC for ANS from 0. 16 to 1. 10 per molecule of protein after HHP treatment for 30 min. No significant changes in the apparent dissociation constant of WPC for ANS were observed after HHP treatment, except for an increase from 1. 8 X 10(-5) M to 3.3 x 10(-5) M after 30 min of HHP treatment. There were no significant changes in the number of binding sites of WPC for CPA. However, increased binding affinities of WPC for CPA were observed after the come-up time or 10 min of HHP treatment, with a decrease of apparent dissociation constant from 2.2 x 10(-7) M to 1. 1 X 10(-7) M. The binding sites of WPC may become more accessible to the aliphatic hydrophobic probe CPA after the come-up time or 10 min of HHP treatment. These results indicate that HHP treatment of WPC yields increases in the number of binding sites for an aromatic hydrophobic probe, while aliphatic hydrophobic binding affinity of WPC is enhanced after come-up time or 10 min of HHP treatment. (c) 2005 Elsevier Ltd. All rights reserved.