Optimisation of aqueous two-phase extraction of anthocyanins from purple sweet potatoes by response surface methodology

Aqueous two-phase extraction (ATPE) method was investigated for extraction of anthocyanins from purple sweet potatoes using response surface methodology (RSM). Results showed that the optimal conditions for anthocyanin extraction were that, 45:1 (mL/g) liquid–solid ratio, 25% (W/W) ethanol, 22% (W/W) concentration of ammonium sulphate and pH3.3; the anthocyanin yield and partition coefficient under the optimal conditions were 90.02% and 19.62, respectively. The result of HPLC-ESI-MS analysis revealed eight kinds of compounds, and the major anthocyanins as cyanidi-caffeoy-fumaroy-sophoroside-3-O-glucoside, peonidin-caffeoyl-hydroxybenzoyl-3-O-glucoside, peonidin-caffeoyl-sophoroside-3-O-glucoside, and peonidin-caffeoyl-fumaroyl-sophorosid-3-O-glucoside. Meanwhile, we found a compound as a dimer of galloyl procyanin. These results suggest that ATPE is efficient in extracting anthocyanins and has the potential to be used in natural anthocyanin extraction industry.