Influence of competitive adsorption on flocculation and rheology of high-pressure-treated milk protein-stabilized emulsions

The effect of high-pressure treatment (HPT) on the droplet-size distributio n and small-deformation rheology of oil-in-water emulsions containing beta- lactoglobulin and a nonionic surfactant or sodium caseinate has been invest igated at neutral pH. Addition of Tween 20 (polyoxyethylenesorbitan monolau rate) to a beta-lactoglobulin-stabilized emulsion results in competitive di splacement of the adsorbed globular protein film and, following HPT, the fo rmation of a less flocculated emulsion. The age of the beta-lactoglobulin-s tabilized emulsion prior to addition of sodium caseinate influences the com petitive adsorption behavior. The strengthening of the beta-lactoglobulin l ayer with time makes it more resistant to disruption by sodium caseinate. T he level of pressure-induced flocculation of beta-lactoglobulin-coated oil droplets depends on the intensity of processing conditions and on the degre e of interfacial displacement. In contrast, beta-lactoglobulin added after emulsification appears to show little evidence of competitive adsorption be havior at the caseinate oil-water interface. Changes in the rheological pro perties of these latter systems following HPT can be attributed to pressure -induced denaturation and gelation of beta-lactoglobulin in the continuous phase of the emulsion.