46C-9 |
Nuclear magnetic resonance (NMR) study on the electron donating ability of b-carotene by using 2,2-diphenyl-1-picrylhydrazyl (DPPH) |
J. H. LEE and D. B. Min. Department of Food Science and Technology, The Ohio State University, 2015 Fyffe Court, Columbus, OH 43210-1007 b-Carotene is an excellent singlet oxygen quencher and free radical scavenger. However, the free radical scavenging mechanism of b-carotene has not been scientifically reported. The objective of this study was to determine the free radical scavenging mechanism of b-carotene by using 1H NMR and spectroscopy. Ten mL of 0.05 mM DPPH containing 0, 0.05, 0.1, 0.2, or 0.5 mM b-carotene in acetone were prepared triplicate in 30-mL bottles. The concentration of DPPH was measured at 517 nm every 30 min for 5 hr at 25°C. Samples of 0.05 mM DPPH containing 0.05 mM b-carotene were prepared in CDCl3 with TMS as internal standard. Samples of 0.05 mM DPPH with 0.05 mM BHA in CDCl3 were used as controls. Samples were prepared in duplicate. NMR spectra of samples were measured every 10 min for 60 min by using a 400 MHz NMR, Bruker DPX-400. As the concentrations of b-carotene increased from 0 to 0.5 mM in acetone, the concentration of DPPH decreased from 15 to 75% for 5 hr, which indicates the free radical scavenging ability of b-carotene. NMR spectra of the samples containing the mixture of DPPH and b-carotene were the same for 60 min. However, NMR spectra of the samples containing the mixture of DPPH and BHA, which is a well-known hydrogen donating free radical scavenger, changed as the reaction time increased from 0 to 60 min. The new peak at 5.0 (d) for DPPH in the presence of BHA was formed. One peak at 6.6 (d) from BHA was split into 2 peaks by donating hydrogen. b-Carotene acted as free radical scavenger by donating electron. Data from 1H NMR clearly indicates that b-carotene may not be a hydrogen donating antioxidant in lipid oxidation.
Session 46C, Food Chemistry: Lipids, antioxidants and emulsifiers
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