Formation of a Gel from ß-Lactoglobulin Under Hydrostatic Pressure

Abstract

The ß-lactoglobulin (ß-Lg) concentration required for inducing gelation was 10% at 800 MPa, 12% at 600 MPa and 18% at 400 MPa, but these gels were too soft for any measurement of their textural properties. The hardness and breaking stress of the gels from 14% ß-Lg were both enhanced by increasing the pressure to 800 MPa, but not by increasing the pressurizing time. The microstructure of the ß-Lg gel resembled a honeycomb in the alkaline pH region and coral in the acidic pH region. The secondary structure of soluble protein from the gel showed an almost unchanged α-helix, while the P-structure had disappeared, and random and ß-turns had increased. The solubility of ß-Lg was lower in a Tris-glycine-EDTA buffer at pH 8.0 than in the same buffer containing 0.5% SDS and 8 M urea. In the alkaline pH region, a high-molecular-weight aggregate in addition to a tetramer and di- mer of ß-Lg was detected, but not at pH 4. The SH content of gelled ß-Lg was decreased by pressurization in the alkaline pH region. No gel was formed with more than 10 mM NEM under pressure. At pH 7 or more, the oxidation of SH and exchange of SH-SS in the ß-Lg molecules were essential for the pressure-induced gelation.