EFFECT OF HIGH-PRESSURE TREATMENT OF PROTEIN ON THE RHEOLOGY OF FLOCCULATED EMULSIONS CONTAINING PROTEIN AND POLYSACCHARIDE

We report on the effect of high-pressure treatment (up to 7 kbar) on t he rheology of concentrated emulsions containing the globular protein, bovine serum albumin (BSA), and the anionic polysaccharide dextran su lfate. Small-deformation rheological properties have been determined f or oil-in-water emulsions (40 vol % n-tetradecane, 2.7 wt % BSA, pH 7) containing polysaccharide added after emulsion formation. In the abse nce of high-pressure treatment, a plot of complex shear modulus G at 1 Hz and 30 degrees C against polysaccharide concentration Cp shows a maximum in G at Cp approximate to 0.1 wt % which is consistent with b ridging flocculation caused by a net attractive electrostatic protein- polysaccharide interaction at the emulsion droplet surface. High-press ure treatment of BSA before emulsification, for 30 min at a pressure i n the range of 400-700 MPa, leads to substantial changes in the floccu lation and rheological behavior of the emulsion after polysaccharide a ddition but no discernible change in the emulsion droplet-size distrib ution prior to the addition. In contrast, heat treatment of BSA at 70- 80 degrees C before emulsification leads to an increase in average dro plet size and to changes in emulsion rheology (following addition of p olysaccharide) that are qualitatively different from those found with the pressure-treated systems. These results are discussed in relation to current knowledge about effects of high-pressure processing on prot ein structure and functionality.