Microstructure of β-lactoglobulin-stabilized emulsions containing non-ionic surfactant and excess free protein:: Influence of heating

The influence of the non-ionic surfactant Tween 20 oil the microstructure of beta-lactoglobulin-stabilized emulsions with substantial excess free protein present was investigated via confocal microscopy. The separate distributions of oil droplets and protein were determined using two different fluorescent dyes. In the emulsion at ambient temperature the excess protein and protein-coated oil droplets were associated together in a reversibly flocculated state. The pore-size distribution of the initial flocculated emulsion was found to depend oil the surfactant/protein ratio R, and at higher Values of R the system became more inhomogeneous due to areas of local phase separation. Evidence for competitive displacement of protein from the oil-water interface by surfactant was obtained only oil heating (from 25 to 85 degrees C) during the process of formation of a heat-set emulsion gel. By measuring fluorescence intensities of the protein dye inside and Outside of the oil-droplet-rich areas, we have been able to quantify the evolving protein distribution during the thermal processing. The results are discussed it) relation to previous work on the competitive adsorption of proteins and surfactants in emulsions and the effect of emulsion droplets oil the rheology of heat-set protein gels. (c) 2005 Elsevier Inc. All rights reserved.