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

The foaming behaviour of the beta -lactoglobulin + dextran sulfate (DS) mix ture was investigated by recording the small pressure changes in the head s pace above the collapsing foam in a closed container. The foaming ability w as 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-o rder 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 t hose based on the differential pressure monitoring technique. Foaming was s tudied at a beta -lactoglobulin/DS weight ratio of 3 with the protein conce ntration of 0.15 wt.-% at pH 7.0. The surface tension measurements showed n o change in the activity of protein upon addition of DS. Pressure treatment (0-800 MPa) of pure protein solution indicated no change in the foamabilit y and foam stability. Pressure-treated solutions of beta -lactoglobulin + D S showed an improvement in the foaming ability and a reduction in foam stab ility suggesting that polysaccharide molecules prevent protein molecules ag ainst aggregation.