Isolation and identification of an antioxidant substance from heated garlic (Allium sativum L.)

The objectives of this study were to identify antioxidant substance in heated garlic juice (HGJ). We evaluated the antioxidant activities of heated garlic juice exposed to 120, 130, and 140 degrees C for 2 hr. The HGJ was partitioned using the solvents of hexane, chloroform, ethyl acetate, butanol, and water. The ethyl acetate fraction of HGJ treated at 130 degrees C for 2 hr showed strong antioxidant activity; this extract was isolated and purified using silica gel column chromatography and semi-preparative high-performance liquid chromatography. The structure of the purified compound was determined using spectroscopic methods, i.e., ultraviolet, mass spectrometry, infrared, H-1 NMR, C-13 NMR, DEPT, HMBC, and HMQC. The isolated compound was identified as thiacremonone (2,4-dihydroxy-2,5-dimethyl-thiophene-3-one). Thiacremonone showed strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-scavenging activity, with a 50% inhibition concentration (IC50) of 22.25 +/- 0.44 mu g/mL, which is much higher than that of the antioxidants ascorbic acid (30.06 +/- 0.42 mu g/mL), alpha-tocopherol (71.30 +/- 0.97 mu g/mL), and butylated hydroxyanisole (50.54 +/- 0.94 mu g/mL).