Influence of Emulsifier on the Competitive Adsorption of Whey Proteins in Emulsions

The influence of Tween 20 (polyoxyethylene sorbitan monolaurate) on the composition of adsorbed protein films in hydrocarbon oil-in-water emulsions containing B-lactoglobulin and a-lactalbumin has been investigated at neutral pH. The kinetics of pol ymerization of adsorbed 13-lactoglobulin via sulphydryl-disulphide interchange is little affected by Tween 20. Add ing emulsifier after homogenization leads to slightly greater competitive d i splacement of protein from the interface for emul sions made with pure 8-lactoglobulin than for equivalent emulsions made with 0.-lactalbumin . For emulsions made with the two proteins in a 1 : 1 molar ratio, adding emulsifier after homogeniza t ion leads to more displacement of 8-l actoglobulin than a-lactalbumin. I n a n emulsion containing both proteins a nd Tween 20 added before homogenization at an emulsifier -toprotein molar ratio of 2:1, there i s three times as much a-lactalbumin adsorbed at the droplet surface as S-lactoglobulin. It appears that the kinetics of compe t itive protein exchange between the bulk phase and the oil-water interface is facilitated by the presence of water-soluble surfactant