30A-20 |
The effects of chlorophyll, light and oxygen on the stability of 2,2-diphenyl-1-picrylhydrazyl radical in acetone and soybean oil |
B. OZCELIK1, J. Lee2, and D. B. Min2. (1) Food Engineering Department, Istanbul Technical University, Maslak-Istanbul 80626, Istanbul, 80626, Turkey, (2) Department of Food Science & Technology, The Ohio State University, 2015 Fyffe Court, columbus, OH 43210-1007 The 2,2-diphenyl-1-picrylhydrazyl radical (DPPH) has been used as a model free radical compound to evaluate the effectiveness of antioxidants. DPPH are considered to be very stable and to be destroyed only by antioxidants which can donate hydrogen atom. That is, the more effective the compound in destroying DPPH, the better the compound as antioxidant. To study the effects of light, oxygen, and chlorophyll on the stability of DPPH in acetone and soybean oil. The 30mL bottles containing 20mL of 0.05mM DPPH in acetone were prepared. Some samples were stored at 45oC under the dark or the light of 4,000 lux. Some bottles were flushed with nitrogen gas for 30 minutes to remove the dissolved and headspace oxygen. Some bottles were added with chlorophyll to get 4 ppm concentration to study the effect of singlet oxygen on the DPPH. The destruction of DPPH was measured at 517 nm every 30 minutes for 2 hr. The headspace oxygen contents of 2mL soybean oil containing 4 ppm chlorophyll in acetone with or without 0.05mM DPPH in 30mL vials were analyzed by gas chromatography. The DPPH in acetone was not changed under dark, but decreased by 20% under light for 1hr. The oxygen or chlorophyll did not affect the stability of DPPH under dark. The DPPH in acetone with chlorophyll was destroyed 7% more than without chlorophyll for 1 hr under light, which may be due to the reaction of DPPH with singlet oxygen produced by chlorophyll under light. The headspace oxygen contents of soybean oil with or without DPPH for 2 hours under light at 45oC were 12.5 or 16.3%, respectively, which indicated that DPPH acted as a pro-oxidant in soybean oil by providing free radicals. The destruction measurement of DPPH to evaluate the antioxidant effectiveness should be interpreted very carefully since DPPH can be destroyed by light or singlet oxygen.
Session 30A, Food Chemistry: Lipids
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