Changes in protein-protein and protein-polysaccharide interactions induced by high pressure

β-Lactoglobulin and bovine serum albumin (BSA) protein solutions (0.1%, 0.2% and 2.5%), when subjected to high pressure treatment (800 MPa for 20 min) at neutral pH, were denatured and some aggregates formed. The total calorimetric enthalpy of 2.5% solutions of the pressure-treated proteins decreased to virtually zero for both β-lactoglobulin and BSA following pressure treatment. Isoelectric focussing patterns (IEF) indicated that aggregation occurred in both proteins and there was a concomitant loss of sulphydryl groups (42% for β-lactoglobulin and 55% for BSA), suggesting that protein aggregation after high pressure processing was caused, at least in part, by the formation of -S-S- bridges. The surface hydrophobicity of the two proteins was modified, increasing (40%) with β-lactoglobulin and decreasing (41%) with BSA. Pressure treatment of 1:1 mixtures of BSA and dextran sulphate (DS) yielded structures with a significant enthalpy. However, addition of DS to β-lactoglobulin had little effect on the thermograms, suggesting that the DS either protects the protein against pressure induced unfolding or enables the pressure-denatured protein to regain some secondary structure.