2022 Annual Meeting
The Amphoteric Surfactant N,N?Dimethyldodecylamine N?Oxide Unfolds ??Lactoglobulin Above the Critical Micelle Concentration
The understanding of protein-surfactant interactions is important for the formulation and processing of many consumer products. The structure of protein-surfactant systems is complex and can influence enzymatic activity, binding to surfaces, and foam and emulsion development. While detailed studies have been performed looking at how proteins interact with anionic and cationic surfactants, less is known about their interactions with amphoteric surfactants such as N,N-dimethyldodecylamine N-oxide (DDAO) which is often used for protein membrane extraction and as a foam booster in detergent formulations. In this study, biophysical characterization techniques including small angle x-ray scattering (SAXS) were used to investigate how DDAO impacts the structure of the globular protein β-lactoglobulin (βLG) at pH 8. Results from pyrene fluorescence and pendant drop tensiometry showed βLG does not significantly impact DDAOâs critical micelle concentration (CMC). Circular dichroism (CD) demonstrated βLG unfolding due to interactions with DDAO at concentrations above its CMC. SAXS results were used to determine the size of the protein-surfactant complexes and confirmed the CD results showing that DDAO has little impact on conformation of βLG below its CMC. At concentrations greater than the CMC DDAO unfolds βLG and the resulting structure resembles a protein-decorated micelle. This is different than what is observed with the anionic surfactant sodium dodecyl sulfate (SDS) and βLG where structural changes are observed at concentrations well below the CMC.