Preparative Isolation and Purification of Three Anthocyanins from Red Raspberry (Rubus ideaus L.) Fruits by High-Speed Counter-Current Chromatography Based on the Optimization of the Ultrasound-Assisted Extraction Method

Anthocyanins are a sort of important natural pigments in red raspberry which have many pharmacological effects. First, the ultrasound-assisted extraction (UAE) of total anthocyanins was optimized by Box–Behnken design (BBD) in this study. The detailed optimized method which has the advantages of high extraction rate and short time was as follows: the ultrasonic extraction temperature was 20 °C, the solvent to sample ratio was 26 mL/g, and the pH value was 3. The total anthocyanin content extracted from thawed red raspberry was 9.178 mg/100 g. Then, the crude extracts obtained from red raspberry fruits with 80% ethanol were isolated with a macroporous resin column (AB-8) and eluted with ethanol in gradient elution. Third, the system of a two-phase solvent, which consisted of n-butanol, methyl tert-butyl ether (MTBE), acetonitrile, water, and trifluoroacetic acid (5:1:1:4:0.001, v/v), was applied for high-speed counter-current chromatography (HSCCC). Finally, three anthocyanin compounds were identified as cyanidin-3-O-sophoroside, cyanidin-3-O-(2G-O-glucosylrutinoside), and cyanidin-3-O-glucoside by UV, MS, and NMR analyses, and their purities were 95.35%, 91.31%, and 99.12%, respectively. This study demonstrated an effective procedure of extraction and purification for anthocyanins from red raspberry fruits, which could provide interesting information for the in-depth study of bioactive compounds of red raspberry fruits.