Abstract
Nine synthetic amphiphilic phenolic lipids, varied in phenolic moiety (caffeoyl/dimethylcaffeoyl) and fatty acid chain lengths (8-18) were characterized by differential scanning calorimetry (DSC), temperature-ramp Fourier transform infra-red spectroscopy (FT-IR) and atomic force microscopy (AFM). FT-IR and DSC results revealed that the physical state and lateral packing of synthetic molecules were largely governed by fatty acyls. The critical micelle concentrations (CMC) of synthetic lipids was in the range of 0.1 mM to 2.5 mM, affording generation of stable oil-in-water emulsions; as evidenced by the creaming index (<5%) of emulsions stabilized by compounds C12‒C16, and C12a‒C16a after 7 days' storage. AFM analysis revealed that compound C14 formed stable double-layers films of 5.2 nm and 6.7 nm. Application studies showed that formulations stabilized by synthesized compounds containing 30% fish oil had superior physical and oxidative stability compared to formulations containing commercial emulsifiers or their mixtures with phenolic acids. Moreover, the synthetic compounds were non-toxic against in vitro transformed keratinocytes from histologically normal skin and Caco-2 cell lines. This study demonstrates the relevance of using a natural hydroxycarboxylic acid as a flexible linker between natural antioxidants, glycerol and fatty acids to generate multifunctional amphiphiles with potential applications in food, pharmaceutical and cosmetic industry.