Characterization of Free Radicals in Soluble Coffee by Electron Paramagnetic Resonance Spectroscopy
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- 作者：Ederlinda C. Pascual ; Bernard A. Goodman ; and Chahan Yeretzian
- 刊名：Journal of Agricultural and Food Chemistry
- 出版年：2002
- 出版时间：October 9, 2002
- 年：2002
- 卷：50
- 期：21
- 页码：6114 - 6122
- 全文大小：215K
- 年卷期：v.50,no.21(October 9, 2002)
- ISSN：1520-5118
文摘
EPR spectra of soluble coffee display single-line free radical signals in both the solid state and aqueoussolution, along with signals from the paramagnetic ions Fe(III) and Mn(II). The intensity of the freeradical signal in the pure solid was estimated to be ca. 7.5 × 1016 unpaired electrons/g, and therewas no significant change on dissolution in water. In aqueous solutions, however, the free radicalsignal declined rapidly over ca. 10-15 min in the temperature range 20-65 
C, after which onlyslow changes were observed. This decline, which was essentially independent of atmosphere, wasgreatest for the lowest temperatures used, and the intensity after 1 h fitted well to an exponentialcurve with respect to temperature. The free radicals responsible for the single-peak EPR signal didnot react with any of the spin traps tested in the present experiments, but unstable free radicals withparameters consistent with adducts of C-centered radicals were detected in coffee solutions in thepresence of PBN and 4-POBN spin traps. The presence of oxygen in the solutions increased theinitial rate of formation of these free radical adducts. No adducts were detected when DEPMPO wasused as spin trap. However, 
OH adducts of DEPMPO were shown to be unstable in the presenceof coffee, a fact which illustrates the strong free radical scavenging ability of coffee solutions.Keywords: Coffee; oxidation; EPR spectroscopy; free radicals; transition metal ions
C, after which onlyslow changes were observed. This decline, which was essentially independent of atmosphere, wasgreatest for the lowest temperatures used, and the intensity after 1 h fitted well to an exponentialcurve with respect to temperature. The free radicals responsible for the single-peak EPR signal didnot react with any of the spin traps tested in the present experiments, but unstable free radicals withparameters consistent with adducts of C-centered radicals were detected in coffee solutions in thepresence of PBN and 4-POBN spin traps. The presence of oxygen in the solutions increased theinitial rate of formation of these free radical adducts. No adducts were detected when DEPMPO wasused as spin trap. However, OH adducts of DEPMPO were shown to be unstable in the presenceof coffee, a fact which illustrates the strong free radical scavenging ability of coffee solutions.Keywords: Coffee; oxidation; EPR spectroscopy; free radicals; transition metal ions