High pressure effect on foaming properties of beta-lactoglobulin and dextran sulfate mixture.

The foaming behaviour of the beta-lactoglobulin + dextran sulfate (DS) mixture was investigated by recording the small pressure changes in the head space above the collapsing foam in a closed container. The foaming ability was based on the highest pressure obtained from the complete decay of foam. The foam stability was based on the foam decay rate constant of the first-order kinetic law calculated from the pressure change as a function of time. The foamability and foam stability were also assessed in terms of visual measurements of foam half-life and initial foam volume. A good correlation was found between foam stability results based on visual measurements and those based on the differential pressure monitoring technique. Foaming was studied at a beta-lactoglobulin/DS weight ratio of 3 with the protein concentration of 0.15 wt.-% at pH 7.0. The surface tension measurements showed no change in the activity of protein upon addition of DS. Pressure treatment (0-800 MPa) of pure protein solution indicated no change in the foamability and foam stability. Pressure-treated solutions of beta-lactoglobulin + DS showed an improvement in the foaming ability and a reduction in foam stability suggesting that polysaccharide molecules prevent protein molecules against aggregation.