PROCESS-INDUCED CHANGES IN MOLECULAR-STRUCTURE THAT ALTER ADSORBED LAYER PROPERTIES IN OIL-IN-WATER EMULSIONS STABILIZED BY BETA-CASEIN TWEEN20 MIXTURES/

Competitive adsorption of purified B-casein and the non-ionic surfacta nt Tween20 has been investigated in model oil-in-water emulsions. The emulsions were characterised by measurement of droplet size distributi on and specific surface area as a function of surfactant content. The distributions of beta-casein and Tween20 between the subnatant and the adsorbed layer were measured. The results revealed subtle but importa nt differences that are dependent upon the processing history of the c omponents. Further studies examining the effect of Tween20 on the exte nt of interactions formed between B-casein molecules adsorbed at the i nterfaces of oil-water thin films using the fluorescence recovery afte r 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 s upporting these observations was provided by thin layer chromatography . The process-induced change in emulsifier structure has important imp lications for the formulation of food and non-food emulsions. In parti cular, emulsion formulations based on the HLB method may fail due to h omogenisation-induced changes in the emulsifier's HLB during homogenis ation. In addition, our findings resolve apparent contradictions arisi ng from a number of competitive adsorption studies reported in the lit erature.