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Time‐dependent competitive adsorption of milk proteins and surfactants in oil‐in‐water emulsions
Author(s) -
Chen Jianshe,
Dickinson Eric
Publication year - 1993
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740620312
Subject(s) - emulsion , pulmonary surfactant , chemistry , adsorption , chromatography , sorbitan , casein , beta lactoglobulin , chemical engineering , whey protein , organic chemistry , biochemistry , fatty acid , fatty acid ester , engineering
Competitive adsorption of pure milk proteins and non‐ionic surfactants has been studied in model oil‐in‐water emulsions (4 g kg −1 β‐lactoglobulin or β‐casein, 200 g kg −1 n ‐hexadecane) as a function of the age of the adsorbed protein layer at the oil‐water interface. With β‐lactoglobulin‐stabilised emulsions containing oil‐soluble surfactant C 12 E 2 (diethylene glycol n ‐dodecyl ether), there is found to be a steadily increasing amount of protein associated with the emulsion droplets over a few hours following emulsification. Addition of water‐soluble surfactant Tween 20 (polyoxyethylene (20) sorbitan monolaurate) to a β‐lactoglobulin‐stabilised emulsion (with or without C 12 E 2 ) leads to less protein displacement if the emulsion is aged prior to addition of Tween 20. Moderate additions of C 12 E 2 or Tween 20 produce no time dependence in the competitive adsorption in β‐casein‐stabilised emulsions, although some time dependence is observed when C 12 E 2 and a high concentration of Tween 20 are present together. Crystallisation of the oil phase in β‐casein‐stabilised emulsions at pH 7 leads to a lowering of the measured protein surface concentration, especially in the presence of C 12 E 2 and a reduction in the surfactant to protein molar ratio required for complete protein displacement by water‐soluble surfactant (Tween 20 or octaethylene glycol n ‐dodecyl ether). Under more acidic conditions of pH 5 or pH 3, the surface coverage and ease of displacement of β‐lactoglobulin at the surface of liquid emulsion droplets is substantially different from that under neutral pH conditions.