Quantification of unadsorbed protein and surfactant emulsifiers in oil-in-water emulsions

Unadsorbed emulsifiers affect the physical and chemical behaviour of oil-in-water (O/W) emulsions. A simple methodology to quantify unadsorbed emulsifiers in the aqueous phase of O/W emulsions has been developed. Emulsions were centrifuged and filtered to separate the aqueous phase from the oil droplets and the concentration of unadsorbed emulsifiers in the aqueous phase determined. The quantification of unadsorbed surfactants based on the direct transesterification of their fatty acids was validated for Tween 20, Tween 80, citric acid ester (Citrem), Span 20 and monolauroyl glycerol. To determine unadsorbed proteins, results obtained with Folin–Ciocalteu reagent or UV-spectrophotometry were compared on emulsions stabilized by β-lactoglobulin (BLG), β-casein (BCN) or bovine serum albumin (BSA). The first method gave more accurate results especially during aging of emulsions in oxidative conditions. The whole methodology was applied to emulsions stabilized with single or mixed emulsifiers. This approach enables optimization of emulsion formulations and could be useful to follow changes in the levels of unadsorbed emulsifiers during physical or chemical aging processes.

Graphical abstractThe unadsorbed emulsifiers, present in the aqueous phase of O/W emulsions are quantified following a methodology adapted to the class of emulsifiers (surfactants or proteins).Figure optionsDownload full-size imageDownload high-quality image (105 K)Download as PowerPoint slideResearch highlights► The aqueous phases separated from droplets of emulsions by centrifugation and filtration. ► Direct transesterification of surfactant fatty acids in the aqueous phases of emulsions. ► Method validated for Tween 20, Tween 80, Citrem, Span 20 and monolauroyl glycerol. ► Method valid for surfactants mixed with protein. ► UV-spectrophotometry not valid for quantification in oxidative conditions.