We evaluated antioxidant activities of heated pear juice (HPJ) exposed to 120, 130, and 140°C for 2 hr. HPJ was partitioned using n-hexane, chloroform, ethyl acetate, n-butanol, and water. The ethyl acetate fraction treated at 130°C for 2 hr showed strong antioxidant activity; thus, this extract was isolated and purified using silica gel column chromatography and preparative high performance liquid chromatography. The structure of the purified compound was determined using ultraviolet and mass spectrometry, (1)H-nucelar magnetic resonance (NMR), and (13)C-NMR. Antioxidant activities of the isolated compound were evaluated and compared with α-tocopherol, ascorbic acid, and butylated hydroxytoluene (BHT) using DPPH and ABTS assays. The isolated compound was identified as 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one (DDMP). The DPPH radical-scavenging activity (IC50) of DDMP occurred in the following order: ascorbic acid (45.3 μg/mL)> α-tocopherol (69.2 μg/mL)> DDMP (241.6 μg/mL)> BHT (268.0 μg/mL). Furthermore, DDMP showed strong ABTS radical-scavenging activity (569.0 mg AA eq/g).
Keywords: 2,3-dihydro-3,5-dihydroxy-6-methyl-4H-pyran-4-one; antioxidant activity; heat treatment; pear.