Efficient and safe extraction of an antioxidant, 3,5,4’-trihydroxy-6,7-methylenedioxyflavone-3-O-glycoside, from indigo leaves using alkaline hydrolysis of modifying ester moieties

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Indigo plant (Persicaria tinctoria (Aiton) Spach) has been utilized as a dye material with antioxidant activity. To increase polyphenol yield, alkaline water was used for the extraction of indigo leaves. Total polyphenol content and hydrophilic oxygen radical absorbance capacity value of the alkaline water extract were higher than those of the pure water extract, whereas its β-carotene bleaching inhibitory activity and 1,1-diphenyl-2-picrylhydrazyl radical scavenging activity were lower. The predominant compound in the alkaline water extract was 3,5,4′-trihydroxy-6,7-methylenedioxyflavone (TMF)-3-O-β-d-glucopyranoside. β-Carotene bleaching inhibitory activity of TMF was higher than those of TMF-O-glycosides. TMF-3-O-β-d-glucopyranoside was hydrolyzed by β-glucosidase from rat small intestine most effectively among the TMF-O-glycosides. Our results showed that alkaline water extraction of indigo leaves is a useful method to increase the recovery of polyphenols, in which TMF-3-O-β-d-glucopyranoside is the predominant compound, which can be easily hydrolyzed in the small intestine to TMF with high antioxidant activity against lipid peroxidation.