Effect of high pressure on the emulsifying behaviour of beta-lactoglobulin

The influence of high pressure (up to 800 MPa) on the emulsifying behaviour of beta-lactoglobulin has been investigated at neutral pH. Fine oil-in-water emulsions (0.4% w/w beta-lactoglobulin, 20% v/v oil) made with the pressure-treated protein were found to give substantially larger droplets than those made with the native protein. Visual creaming behaviour and changes in average droplet size have been monitored as a function of storage time. There is a consistent trend of decreasing emulsifying efficiency and (especially) reduced emulsion stability with increasing applied pressure and treatment time. The results are interpreted in terms of pressure-induced unfolding of beta-lactoglobulin in aqueous solution, which leads to a loss of emulsifying efficiency due to protein aggregation, despite the increase in surface hydrophobicity, which is confirmed here experimentally. In contrast, high pressure treatment of the corresponding emulsions prepared with the native protein induces only a slight reduction in emulsion stability as reflected in the average droplet size. It appears that the structure of partially unfolded beta-lactoglobulin in the adsorbed monolayer at the surface of the emulsion droplets may be relatively unaffected by the pressure treatment.