Extracts, Fractions, and Subfractions from Purple-Orange Sweet Potato ( L.): Xanthine Oxidase Inhibitory Potential and Antioxidant Properties.

Previous research has shown that fractions outperformed extracts in pharmacological activity and safety. This study assessed the total phenol and flavonoid content, as well as antioxidant and xanthine oxidase inhibitory (XOI) activities, of purple-orange sweet potato extracts, fractions, and subfractions. Using UV-visible spectrophotometry, the leaves showed the highest values for total phenol, flavonoid, 2,2-diphenyl-1-picrylhydrazyl (DPPH), Ferric Reducing Antioxidant Power (FRAP), Cupric Ion Reducing Antioxidant Capacity (CUPRAC) assays, and XOI activity. The sequential extraction of the leaves yielded ethyl acetate extract as the most potent, with a yield of 10.4%, a DPPH assay result of 511.212 ± 0.416 mg ascorbic acid equivalent antioxidant capacity (AEAC)/g, and XOI activity of 45.192 ± 4.981 mg allopurinol equivalent xanthine inhibitory capacity (AEXIC)/g. CF5 had the greatest DPPH assay (158.475 ± 0.170 mg AEAC/g), FRAP assay (86.849 ± 0.048 mg AEAC/g), CUPRAC assay (1008.892 ± 1.620 mg AEAC/g), and XOI activity (6.062 ± 1.730 mg AEXIC/g) values. Subfraction CSF3 from fraction CF5 was analyzed using UPLC-MS/MS and revealed the presence of compounds such as cholest-4-en-3-one, 4-hydroxy-6-[2-(2-methyl-1,2,4a,5,6,7,8,8a-octahydronaphthalen-1-yl) ethyl] oxan-2-one, tangeritin, 4-methyl benzophenone, benzophenone, (+)-ar-turmerone, 4-methoxycinnamic acid, and ricinine. This study was the first to report xanthine oxidase inhibitory activity in allopurinol equivalence. The leaves of the purple-orange sweet potato showed potential as a source of natural antioxidants.