In vitro activity-guided identification of antioxidants in aged garlic extract

Activity-guided fractionation was applied on an aged garlic extract (AGE), reported to show strong antioxidant activity, in order to locate the key in vitro antioxidant ingredients by means of the hydrogen peroxide scavenging (HPS) assay as well as the ORAC assay. Besides the previously reported four tetrahydro-β-carbolines, (1R,3S)- and (1S,3S)-1-methyl-1,2,3,4-tetrahydro- β-carboline-3-carboxylic acid and (1R,3S)- and (1S,3S)-1-methyl-1,2,3,4- tetrahydro-β-carboline-1,3-dicarboxylic acid, LC-MS/MS, LC-TOF-MS, and 1D/2D-NMR experiments led to the identification of coniferyl alcohol and its dilignols (-)-(2R,3S)-dihydrodehydrodiconiferyl alcohol, (+)-(2S,3R)- dehydrodiconiferyl alcohol, erythro-guaiacylglycerol-β-O-4′-coniferyl ether, and threo-guaiacylglycerol-β-O-4′-coniferyl ether as the major antioxidants in AGE. The purified individual compounds showed high antioxidant activity, with EC₅₀ values of 9.7-11.8 μM (HPS assay) and 2.60-3.65 μmol TE/μmol (ORAC assay), respectively.