Time-dependent competitive adsorption of milk proteins and surfactants in oil-in-water emulsions

✍ Scribed by Jianshe Chen; Eric Dickinson

• Publisher: John Wiley and Sons
• Year: 1993
• Tongue: English
• Weight: 720 KB
• Volume: 62
• Category: Article
• ISSN: 0022-5142
• DOI: 10.1002/jsfa.2740620312

✦ Synopsis

Abstract

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.