The beta -lactoglobulin ( beta -Lg) concentration required for inducing gelation was 10percent at 800 MPa, 12percent at 600 MPa and 18percent 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 14percent beta -Lg were both enhanced by increasing the pressure to 800 MPa, but not by increasing the pressurizing time. The microstructure of the beta -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 alpha -helix, while the beta -structure had disappeared, and random and beta3-turns had increased. The solubility of beta -Lg was lower in a Tris-glycine-EDTA buffer at pH 8.0 than in the same buffer containing 0.5percent SDS and 8 M urea. In the alkaline pH region, a high-molecular-weight aggregate in addition to a tetramer and dimer of beta -Lg was detected, but not at pH 4. The SH content of gelled beta -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 beta -Lg molecules were essential for the pressure-induced gelation.
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