CHANGES IN PROTEIN-PROTEIN AND PROTEIN-POLYSACCHARIDE INTERACTIONS INDUCED BY HIGH-PRESSURE

beta-Lactoglobulin and bovine serum albumin (BSA) protein solutions (0 .1%, 0.2% and 2.5%), when subjected to high pressure treatment (800 MP a for 20 min) at neutral pH, were denatured and some aggregates formed . The total calorimetric enthalpy of 2.5% solutions of the pressure-tr eated proteins decreased to virtually zero for both beta-lactoglobulin and BSA following pressure treatment. Isoelectric focussing patterns (IEF) indicated that aggregation occurred in both proteins and there w as a concomitant loss of sulphydryl groups (42% for beta-lactoglobulin and 55% for BSA), suggesting that protein aggregation after high pres sure 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 beta-lactoglobulin and decreasing (41%) with B SA. Pressure treatment of 1:1 mixtures of BSA and dextran sulphate (DS ) yielded structures with a significant enthalpy. However, addition of DS to beta-lactoglobulin had little effect on the thermograms, sugges ting that the DS either protects the protein against pressure induced unfolding or enables the pressure-denatured protein to regain some sec ondary structure. Copyright (C) 1996 Elsevier Science Ltd