Volumetric changes to the molecular structure of beta-lactoglobulin processed at high pressure

We measured in-situ the volumetric changes to the molecular structure of the bovine milk protein β-lactoglobulin in a series of high-pressure processing experiments. We used the so-called μPVT device at hydrostatic pressures up to 500 MPa under isothermal conditions of 25 °C, the protein in solution, prepared at both pH 5.0 and 7.0, in a series of compression and decompression cycles. Significant irreversible volumetric changes were found, most notably with a marked step decrease in molar volume of 1.3 litre mol-1 occurring between 10 and 17 MPa. Irreversible molar volume changes of 2.16 litre mol-1 were found when pressures above 17 MPa were applied. This is thought to be due in part to a collapse of the inner calyx. Volume changes were confirmed by measuring the unit-cell volume of the crystalline protein. The effects of pH were indistinguishable. These pressures are considerably less than previously thought necessary for this protein