The acid-induced liquid−liquid phase separation of anionic surfactants in aqueous solutions, and its applicability to cloud point extraction methodology, were examined. The phase diagrams obtained (e.g., [HCl] vs [surfactant]) consisted of three regions:  a homogeneous liquid region, two coexisting isotropic phases, and a solid region. The breadth of each region was found to depend on the surfactant structure. The behavior of each phase was also examined in relation to temperature and added salts. The anionic surfactants investigated were sodium dodecyl sulfate (SDS), sodium dodecylbenzenesulfonic acid (SDBSA), sodium dodecanesulfonic acid (SDSA), and sodium dioctylsulfosuccinate (Aerosol OT). The use of anionic surfactant-mediated phase separations provided very high extraction efficiencies (80−100%) for pyrene in aqueous samples and various PAHs in a certified reference material (dried sewage sludge). The preconcentration factor achieved was found to be a function of both surfactant and acid concentrations. Theoretical preconcentration factors as high as 230 can be reached with Aerosol OT. Alkyl surfactants were used to preconcentrate polar PAHs and progesterone prior to their determination by HPLC. The lack of an aromatic moiety in the structure of the surfactants and their ionic character enables complete resolution of their chromatographic peak from those of the analytes. The ability of anionic surfactants to extract thermally labile compounds was confirmed by extracting vitamin E at 10 °C with recoveries of about 80−85%.

Astaxanthin, a powerful antioxidant, is a good candidate for the prevention of intracellular oxidative stress. The aim of the study was to compare the antioxidant activity of astaxanthin present in two natural extracts from Haematococcus pluvialis, a microalgae strain, with that of synthetic astaxanthin. Natural extracts were obtained either by solvent or supercritical extraction methods. UV, HPLC-DAD and (HPLC-(atmospheric pressure chemical ionization (APCI)+)/ion trap-MS) characterizations of both natural extracts showed similar compositions of carotenoids, but different percentages in free astaxanthin and its ester derivatives. The Trolox equivalent antioxidant capacity (TEAC) assay showed that natural extracts containing esters displayed stronger antioxidant activities than free astaxanthin. Their antioxidant capacities to inhibit intracellular oxidative stress were then evaluated on HUVEC cells. The intracellular antioxidant activity in natural extracts was approximately 90-times higher than synthetic astaxanthin (5 µM). No modification, neither in the morphology nor in the viability, of vascular human cells was observed by in vitro biocompatibility study up to 10 µM astaxanthin concentrations. Therefore, these results revealed the therapeutic potential of the natural extracts in vascular human cell protection against oxidative stress without toxicity, which could be exploited in prevention and/or treatment of cardiovascular diseases.

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Astaxanthin is a xanthophyll carotenoid showing efficient scavenging ability and represents an interesting candidate in the development of new therapies for preventing and treating oxidative stress-related pathologies. However, its high lipophilicity and thermolability often limits its antioxidant efficacy in human applications. Here, we developed a formulation of lipid carriers to protect astaxanthin’s antioxidant activity. The synthesis of natural astaxanthin-loaded nanostructured lipid carriers using a green process with sunflower oil as liquid lipid is presented. Their antioxidant activity was measured by α-Tocopherol Equivalent Antioxidant Capacity assay and was compared to those of both natural astaxanthin and α-tocopherol. Characterizations by dynamic light scattering, atomic force microscopy, and scattering electron microscopy techniques were carried out and showed spherical and surface negative charged particles with z-average and polydispersity values of ~60 nm and ~0.3, respectively. Astaxanthin loading was also investigated showing an astaxanthin recovery of more than 90% after synthesis of nanostructured lipid carriers. These results demonstrate the capability of the formulation to stabilize astaxanthin molecule and preserve and enhance the antioxidant activity.

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