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From olive leaves to spherical nanoparticles by one-step RESS process precipitation

Abstract:

In this work, spherical nanoparticles to be used in cosmetic, agro food or pharmaceutical industries have been directly precipitated from olives leaves in one-step RESS process. The leaves were brought into contact with supercritical CO2, and a fraction of the compounds from the flavone and flavonol families that can be found in the leaves were dissolved; then, by depressurizing the vessel, these compounds formed particles in the nanometer range. A complete factorial design was generated to thoroughly determine the influence from the main parameters on the RESS process with respect to the precipitated nanoparticles and their heterogeneity. Their antioxidant activity was also evaluated. Different pressures (250–350 bar), temperatures (60 and 100 °C), leaves sample weights (2 and 4 g) and cosolvent volumes, namely ethanol (9 and 18 mL), were studied as the main parameters that could affect the solvation and precipitation of the particle with active compounds in the leaves. Other parameters such as contact time (1 h) or nozzle size diameter (100 μm) remained unchanged. The antioxidant activity was evaluated by means of the radical scavenging method using the radical 2,2-diphenyl-1-picrylhydrazole (DPPH). Spherical particles with diameters in the range of 55 nm to 4 µm were obtained. Lower pressures and higher temperatures seemed to result in a reduction of the mean particle size. Greater volume of cosolvent is also recommended to reduce mean particle size. However, lower pressure, temperature and volume of cosolvent seems to promote a greater homogeneity of the particles. By means of chromatographic analyses, the main compounds, responsible for the antioxidant activity, such as oleuropein, quercetin or apigenin among others were identified.