Abstract
The Escherichia coli's membrane protein OmpA has been identified as a potential biosurfactant due to their amphiphilic nature, and their capacity to stabilize emulsions of dodecane in water. In this study, the influence of surfactant type, concentration, preservation time and droplet size on the crystallization of n-dodecane and water, in oil-in-water emulsions stabilized with six rationally designed Escherichia coli's OmpA-based peptides was investigated. A differential scanning calorimetry (DSC) protocol was established using emulsions stabilized with Tween 20® and Tween 80®. A relationship between the surfactant concentration and the crystallization temperatures of n-dodecane and water was observed, where the crystallization temperatures seem to be dependent on the preservation time. A deconvolution analysis shows that the peak morphology possibly depends on the interactions at the interface because the enthalpic contributions of each Gaussian peak remained similar in emulsions stabilized with the same peptide. Adsorption results show that the main driver for adsorption and thus stabilization of emulsions is polar interactions (e.g. H-bonding) through the hydrophilic parts of the peptides. Those peptides with a preponderance of polar interaction groups distribution (i.e. NH2, COOH, imidazole) showed the highest interfacial activity under favorable pH conditions. This suggests that custom-made peptides whose hydrophilic/hydrophobic regions can be fine-tuned depending on the application can be easily produced with the additional advantage of their biodegradable nature.