Precipitation of powerful antioxidant nanoparticles from orange leaves by means of supercritical CO2

Abstract An extensive study has been carried out where CO 2 has been used both as solvent and antisolvent to appreciate orange leaves as a source of powerful antioxidant nanoparticles. In the former case, the leaves were processed directly to yield particles in the nano or micrometer range. In the latter case, a conventional ethanolic extraction of orange leaves was carried out before the orange leaves were subjected to supercritical conditions to extract the particles with high antioxidant activity. Thus, different pressure (80–300 bar), temperature (40–100 °C) and liquid extract concentration (10–42 mg/mL) levels were studied. When CO 2 was used as the solvent, agglomerates with low antioxidant activity precipitated. Higher pressure and temperature levels were required to obtain powder precipitation. However, when CO 2 was used as the antisolvent, polyphenols with high antioxidant activity (3–4.65) in the nanometer range (60–73 nm) would precipitate. The efficiency of the process was determined by the antioxidant compound concentration ratio of the extract. Vessel pressure was the main influencing variable with regards to impact on particle size and antioxidant activity. The smallest particle size and greatest precipitate yields were obtained at high pressure and low temperature.