Conventional, ultrasound-assisted, and accelerated-solvent extractions of anthocyanins from purple sweet potatoes

• Anthocyanin extraction parameters of three extraction methods have been optimized.
• Extraction efficiencies were opposite for anthocyanins, and phenolics/flavonoids.
• Antioxidant values of ORAC and FRAP were different based on extraction methods.
• Anthocyanins in di-, or non- and mono-acyl groups varied with extraction methods.

Purple sweet potatoes (PSPs) are rich in anthocyanins. In this study, we investigated the extraction efficiency of anthocyanins from PSPs using conventional extraction (CE), ultrasound-assisted extraction (UAE), and accelerated-solvent extraction (ASE). Additionally, the effects of these extraction methods on antioxidant activity and anthocyanin composition of PSP extracts were evaluated. In order of decreasing extraction efficiency, the extraction methods were ASE > UAE > CE for anthocyanins (218–244 mg/100 g DW) and CE > UAE > ASE for total phenolics (631–955 mg/100 g DW) and flavonoids (28–40 mg/100 g DW). Antioxidant activities of PSP extracts were CE ≈ UAE > ASE for ORAC (766–1091 mg TE/100 g DW) and ASE > CE ≈ UAE for FRAP (1299–1705 mg TE/100 g DW). Twelve anthocyanins were identified. ASE extracts contained more diacyl anthocyanins and less nonacyl and monoacyl anthocyanins than CE and ASE extracts (P < 0.05).