Phenolics from hull of Garcinia mangostana fruit and their antioxidant activities

The air-dried fruit hulls of Garcinia mangostana Linn. were extracted with 70% MeOH, and then partitioned into the n-BuOH fractions. Furthermore, three major phenolic components related to their antioxidant activities were purified by silica gel column chromatography and Sephadex LH-20 and then identified as P1 (1,3,6,7-tetrahydroxy-2,8-(3-methyl-2-butenyl)), P2 [1,3,6-trihydroxy-7-methoxy-2,8-(3-methyl-2-butenyl) xanthone] and P3 (epicatechin) using UV–visible spectrophotometry, IR spectrophotometry and NMR spectroscopy, respectively. The antioxidant activities of three major phenolics were evaluated using different tests, including the free radical scavenging capability and total antioxidant activity in a linoleic acid peroxidation. These three phenolic compounds exhibited different antioxidant activities in these antioxidant tests. The hydroxyl radical and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capabilities and the activity against linoleic acid peroxidation of P1 were greater than those of P2 and P3, while the superoxide anion radical scavenging activity of P3 was greater than that of P1, but was close to that of P2 or α-tocopherol. An activity-guided isolation and purification process was used to identify the components showing the strong DPPH radical scavenging activity from G. mangostana Linn.