Phenolic Constituents and Antioxidant Properties ofXanthosoma violaceumLeaves

Abstract

An extract of Xanthosoma violaceum leaves was subjected to a polyphenol profile determination, including total polyphenols, and antioxidant activity evaluation. Analysis of the extract resulted in the isolation of a new flavone C-glycoside, apigenin 6-C-β-d-glucopyranosyl-8-C-β-d-apiofuranoside (1), as well as known flavone C-glycosides, including vitexin (2), isovitexin (3), isovitexin 4‘-O-rhamnopyranoside (4), apigenin 6-C-[β-d-glucopyranosyl-(1→6)-β-d-glucopyranoside] (5), and apigenin 6,8-diC-β-d-glucopyranoside (6). The antioxidant activity of the extract was assessed by means of two different in vitro tests: bleaching of the stable 1,1-diphenyl-2-picrylhydrazyl radical (DPPH test) and peroxidation induced by the water-soluble radical initiator 2,2‘-azobis(2-amidinopropane) hydrochloride, on mixed dipalmitoylphosphatidylcholine/linoleic acid unilamellar vesicles (LP-LUV test). In both tests used, the extract and a fraction II showed a significant antioxidant/free-radical scavenging effect (fraction II, EC₅₀ = 11.6 μg/mL) in comparison to α-tocopherol (EC₅₀ = 10.1 μg/mL). Keywords: Xanthosoma violaceum; new cocoyams; C-glycosyl flavones; free-radical scavenging/antioxidant activity