Extraction of anthocyanins from Arrabidaea chica in fixed bed using CO2 and CO2/ethanol/water mixtures as solvents

⿢Extracts of Arrabidaea chica leaves were obtained using scCO2 in a first step and a mixture of scCO2/ethanol/water in a second extraction step.⿢The scCO2 was selective for extracting carajurin which is one of three major anthocyanins.⿢The presence of water in the solvent mixtures was essential to combine high extraction and high recuperation for the compounds of interest.

Leaves of Arrabidaea chica (Humb. Bonpl.) Verlot are rich in anthocyanins and have been used as a medicinal plant in the Amazon region. In order to obtain different extracts from this plant, a sequential extraction in fixed bed was carried out at 40 °C and 300 bar, using supercritical carbon dioxide (scCO2) in a first step, and a mixture containing CO2/ethanol/water at mass ratios of approximately 80/20/0, 80/14/6 and 80/10/10 in a second extraction step. The residue from the second step was extracted with water at 40 °C and atmospheric pressure. Ethanolic, aqueous and hydroalcoholic (70:30, v:v) extracts were also obtained by conventional extraction methods at atmospheric pressure. All extracts were analyzed for global extraction yield, total phenolic content, total flavonoids, and carajurin content. High performance liquid chromatography (HPLC) was used both to quantify carajurin, which is the main anthocyanin component of A. chica, and to monitor qualitatively two other anthocyanin pigments found in that plant. The extraction yield in the first step was only 0.65% using pure scCO2, but this extraction was highly selective to extract carajurin from the three main anthocyanins. The accumulated global yield of the two steps ranged from 3% when the solvent ratio (80/20/0) was used in the second step to about 50% when 6 or 10% water was used, showing the highest yield when the extraction was done with water. The highest contents of total phenolic compounds (178 mg GAE/g extract) and total flavonoids (373 mg EC/g extract) were found in the process performed with the extraction mixture (80/20/0), and the highest carajurin content was obtained in the ethanolic extracts.

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