Melanin and humic acid-like polymer complex from olive mill waste waters. Part II. Surfactant properties and encapsulation in W/O microemulsions

Abstract

A natural melanin and humic acid-like polymer complex from olive mill waste waters (OMWWs) showing surfactant and antiradical properties was encapsulated in food grade water-in-oil (W/O) microemulsions to detect potential interactions with the system's components. Before encapsulation, putative surfactant properties of the polymer complex were investigated through interaction studies with the cationic dye Toluidine blue O (TBO) using spectrophotometry. The limits of the single-phase region corresponding to W/O microemulsions as described by ternary phase diagrams were studied. Structural characteristics of the microemulsions were examined using electrical conductivity, dynamic light scattering (DLS) and electron paramagnetic resonance (EPR) spectroscopy. Antiradical properties of encapsulated polymer complex were investigated using an EPR approach. The existence of a J-aggregation mechanism consisting of head-to-tail arrangement of the dye molecules was proved and attributed to a specific 3D-arrangement of the phenolic constituents of the complex. EPR measurements using the spin probing technique revealed participation of the complex in the surfactants monolayer causing increased membrane fluidity. Droplet size measurements showed a decrease of aqueous droplets size from 19±0.5 to 17±0.8nm upon polymer complex addition. Finally, radical scavenging activity of the complex was retained upon encapsulation and expressed in Trolox equivalents.