Pressurized liquid extraction and quantification of anthocyanins in purple-fleshed sweet potato genotypes

Analysis of anthocyanins responsible for the purple flesh color is important for breeding programs and development of value-added products. This study aimed to optimize the conditions for anthocyanin extraction from purple-fleshed sweet potatoes (PFSP) using pressurized-liquid extraction (PLE) method and quantify anthocyanins in various genotypes. Freeze-dried powders of PFSP genotypes were extracted with acidified methanol using an accelerated solvent extractor. Anthocyanin content of the extract was characterized by (a) pH-differential method and (b) color value protocol measuring absorbance at 530 nm, which is commonly used in Japan as a commercial indicator of total anthocyanin quantity. Highest anthocyanin yields by PLE were with an acetic acid:methanol:water mixture of 7:75:18% (v/v), sample weight of <0.5 g and 80–120 °C. Among 335 genotypes, the anthocyanin content varied widely from 0 to 663 mg cyanidine-3-glucoside equivalent/100 g powder or 0–210 mg/100 g fresh weight. The total monomeric anthocyanin (TMA) contents determined by the pH-differential method were highly correlated with the Japan color value (JCV) protocol, TMA = (0.145) JCV, R2 = 0.943. These results can be useful for sweet potato breeding programs and processing industry in development of PFSP cultivars and processed products with high anthocyanin levels.