HIGH-PRESSURE UNFOLDING AND AGGREGATION OF BETA-LACTOGLOBULIN AND THE BAROPROTECTIVE EFFECTS OF SUCROSE

The effects of processing at 450 MPa and 25 degrees C for 15 min on the unfolding and aggregation of an industrial beta-lactoglobulin protein isolate (beta LG) have been studied at pH 7.0 (at 0.1 MPa) and two protein concentrations, at 0-5% sucrose. After 2.5 or 5% protein solutions (no sucrose) were pressure processed, beta LG remained soluble, but the residual enthalpy of denaturation (Delta H, as determined by DSC 20-27 h after pressurization) was decreased by 44 or 54%, respectively, indicating significant unfolding. Solubility in 2 M ammonium sulfate was similarly decreased, evidencing pressure-induced protein aggregation. Some soluble aggregates (36-10(3) kDa) were observed by gel permeation chromatography. Pressure-induced unfolding or aggregation (at 2.5% protein) was found to be partially reversible with storage time after pressurization (up to 26 or 33%, respectively, of the initial changes, after 7 days at 4 degrees C). The presence of 5% sucrose during pressurization at 2.5% protein reduced beta LG unfolding (Delta H was decreased by 27% instead of 44%) and slightly increased the rate of recovery of protein solubility in 2 M ammonium sulfate.