Alkylpyridiniums. 2. Isolation and Quantification in Roasted and Ground Coffees

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• 作者：Richard H. Stadler ; Natalia Varga ; Christian Milo ; Benoit Schilter ; Francia Arce Vera ; and Dieter H. Welti
• 刊名：Journal of Agricultural and Food Chemistry
• 出版年：2002
• 出版时间：February 27, 2002
• 年：2002
• 卷：50
• 期：5
• 页码：1200 - 1206
• 全文大小：79K
• 年卷期：v.50,no.5(February 27, 2002)
• ISSN：1520-5118

文摘

Recent model studies on trigonelline decomposition have identified nonvolatile alkylpyridiniums asmajor reaction products under certain physicochemical conditions. The quaternary base 1-methylpyridinium was isolated from roasted and ground coffee and purified by ion exchange and thin-layerchromatography. The compound was characterized by nuclear magnetic resonance spectroscopy(¹H, ¹³C) and mass spectrometry techniques. A liquid chromatography-electrospray ionization tandemmass spectrometry method was developed to quantify the alkaloid in coffee by isotope dilution massspectrometry. The formation of alkylpyridiniums is positively correlated to the roasting degree in arabicacoffee, and highest levels of 1-methylpyridinium, reaching up to 0.25% on a per weight basis, werefound in dark roasted coffee beans. Analyses of coffee extracts also showed the presence ofdimethylpyridinium, at concentrations ranging from 5 to 25 mg/kg. This is the first report on the isolationand quantification of alkylpyridiniums in coffee. These compounds, described here in detail for thefirst time, may have an impact on the flavor/aroma profile of coffee directly (e.g., bitterness), or indirectlyas precursors, and potentially open new avenues in the flavor/aroma modulation of coffee.Keywords: Roasted and ground coffee; trigonelline; 1-methylpyridinium; 1,4-dimethylpyridinium;dialkylpyridinium; liquid chromatography-mass spectrometry (LC-MS); nuclear magnetic resonancespectroscopy (NMR)