Evaluation of carbon dioxide supercritical fluid extraction (CO2-SFE) on carotenoids recovery from red yeast cells

In this work, the performance of carotenoids extraction from Rhodotorula spp red yeast (strain ELP2022) using supercritical CO2 (CO2-SFE) was compared to the traditional technique with organic solvent. For this purpose, the yeast was cultured in liquid medium, pre-treated with glass beads in 0.1 M NaHCO3, and lyophilized. The extraction by CO2-SFE was carried out using a bench scale equipment at 300, 400, and 500 bar whilst maintaining a constant CO2 flow rate (6 mL/min) and temperature (40 °C) resulting in an average extraction yields of 60.8 ± 1.1, 68.0 ± 1.4, and 67.6 ± 1.4 µg of total carotenoids per g of yeast (dry weight), respectively. Based on these results, three other experiments at 400 bar and a CO2 flow rate of 6 L/min were also performed. In specific, the temperature was increased up to 60 °C, and ethanol as a co-solvent was added at 40 and 60 °C. The results showed that the temperature does not have a significant effect on the extraction of carotenoids. On the contrary, the yields improved significantly in the presence of the co-solvent, and the percentage of recovery reached the mean values of 71.70% ± 1.4 and 73.86% ± 1.9 at 40 and 60 °C, respectively. Furthermore, from chromatographic analysis, four major peaks were observed and identified as torularhodin, torulene, γ-carotene, and β-carotene which represented about 53.4%, 6.4%, 8.3%, and 26.9% of total carotenoids, respectively. Therefore, these promising results show the potential of this green technique for obtaining high-value products, such as carotenoids, from yeasts and therefore avoiding the use of dangerous solvents.