Ultrasound pre-treatment (UAE) was applied to assist the extraction of valuable compounds (polyphenols (especially anthocyanins), and proteins) from purple sweet potato (PSP). Under optimum conditions (ultrasound time (40min); supplementary hot extraction (80°C) up to 120min; pH: 2.5; ethanol concentration: 58%), the highest concentrations of polyphenols (3.877mg/g), anthocyanins (0.293mg/g), and proteins (0.753mg/g) were found, with minimal specific energy consumption (8406J/mg). Moreover, anthocyanin and non-anthocyanin polyphenols in PSP extract from optimized extraction temperature were identified using HPLC-DAD-ESI-MS(2). The major identified anthocyanins were peonidin-3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside, peonidin-3-(6″-caffeoyl-6‴-feruloyl sophoroside)-5-glucoside, cyanidin-3-caffeoyl-p-hydroxybenzoyl sophoroside-5-glucoside, whereas the major identified non-anthocyanin molecules were quinic acid, chlorogenic acid, caffeic acid, and chlorogenic acid-3-glucose. The amount of the predominant anthocyanin and non-anthocyanin compounds from PSP extract obtained after UAE was higher than that extracted after conventional solvent extraction. The results obtained in this work demonstrated the efficiency of UAE for the recovery of anthocyanins from PSP.
Keywords: Anthocyanins; HPLC-DAD-ESI-MS(2); Polyphenols; Proteins; Purple sweet potato; Ultrasound-assisted extraction.
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