Screening of functional compounds in supercritical fluid extracts from Spirulina platensis

Supercritical fluid extraction and fractionation of Spirulina platensis were carried out in order to obtain functional extracts with antioxidant and/or antimicrobial activities. The β-carotene bleaching method and DPPH free radical-scavenging assay were used to determine the optimal extraction conditions for antioxidant compounds. The best antioxidant extract was obtained in the first fraction when using intermediate pressures and temperatures (220–320 bar, 55 °C), with CO2 plus 10% ethanol as cosolvent, whereas higher pressures and temperatures (320 bar, 75 °C) were needed when pure CO2 was used. Besides, antimicrobial activities of microalgae extracts were tested against four different microbial species, including a gram positive bacterium (Staphylococcus aureus), a gram negative bacterium (Escherichia coli), a yeast (Candida albicans) and a fungus (Aspergillus niger). The most active fraction against all the microorganisms tested, was the one collected in the second fraction in the experiment performed at 220 bar and 26.7 °C with 10% of ethanol.