An innovative method for the purification of anthocyanins from grape skin extracts by using liquid and sub-critical carbon dioxide

This work describes a new and innovative method for the purification of anthocyanins from grape skin extracts as liquid matrix (LM), by using carbon dioxide (CO2). The LM was obtained by extraction of anthocyanins from grape skins using a water/ethyl alcohol solution acidified with 0.2% trifluoroacetic acid (TFA). The CO2 purification process produced a desired fraction (F1) containing pure anthocyanins, and a second fraction (F2) containing ethyl alcohol and other components of the grape skins. An yield of anthocyanin of about 85%, with respect to the starting overall anthocyanin content, was obtained under the following optimized process conditions: pressure 100–130 bar; temperature 30–40 °C; pH of LM 2–4; percentage of ethyl alcohol in the LM 25–30%; CO2 flow rate 25–50 ml/min; LM flow/CO2 flow ratio 3–10%. We have also demonstrated that the purification process allowed to eliminate ethyl alcohol from the anthocyanin extract without any thermal or chemical degradation, obtaining a high added value product which maintains its anthocyanin content and antioxidant activity unchanged.