Process‐Induced Changes in Molecular Structure that Alter Adsorbed Layer Properties in Oil‐in‐Water Emulsions Stabilised by β‐Casein/Tween20 Mixtures

Abstract

Competitive adsorption of purified β-casein and the non-ionic surfactant Tween20 has been investigated in model oil-in-water emulsions. The emulsions were characterised by measurement of droplet size distribution and specific surface area as a function of surfactant content. The distributions of β-casein and Tween20 between the subnatant and the adsorbed layer were measured. The results revealed subtle but important differences that are dependent upon the processing history of the components. Further studies examining the effect of Tween20 on the extent of interactions formed between β-casein molecules adsorbed at the interfaces of oil water thin films using the fluorescence recovery after photobleaching technique have provided evidence of a homogenisation-induced structural change in Tween20 resulting in a major reduction in its hydrophobic-lipophilic balance (HLB) value. Analytical evidence supporting these observations was provided by thin layer chromatography. The process-induced change in emulsifier structure has important implications for the formulation of food and non-food emulsions. In particular, emulsion formulations based on the HLB method may fail due to homogenisation-induced changes in the emulsifier's HLB during homogenisation. In addition, our findings resolve apparent contradictions arising from a number of competitive adsorption studies reported in the literature.