Formation of a Gel from ß-Lactoglobulin Under Hydrostatic Pressure

Abstract

The p-lactoglobulin (P-Lg) concentration required for inducing gelation was J 0% 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% P-Lg were both enhanced by increasing the pressure to 800 MPa, but not by increasing the pressurizing time. The microstructure of the P-Lg gel resembled a honeycomb in the al-kaline pH region and coral in the acidic pH region. The secondary structure of soluble protein from the gel showed an almost unchanged a-helix, while the p-structure had disappeared, and random and p-tums had increased. The solubility of P-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 P-Lg was detected, but not at pH 4. The SH content of gelled P-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 P-Lg molecules were essen-tial for the pressure-induced gelation.