School of Engineering and Science, Centre for Molecular Life Sciences, Jacobs University Bremen, Bremen, Germany.
Food Funct. 2012 Sep;3(9):976-84. doi: 10.1039/c2fo10260a. Epub 2012 Jul 26.
Coffee is one of mankind's most popular beverages obtained from green coffee beans by roasting. Much effort has been expended towards the chemical characterisation of the components of the roasted coffee bean, frequently termed melanoidines, which are dominated byproducts formed from its most relevant secondary metabolites - chlorogenic acids. However, impeded by a lack of suitable authentic reference standards and analytical techniques sufficiently powerful for providing insight into an extraordinarily complex enigmatic material, unsurprisingly little structural and mechanistic information about the products of coffee roasting is available. Here we report on the characterisation of low molecular weight melanoidine fractions of roasted coffee using a conceptually novel combination of targeted and non-targeted mass spectrometrical techniques. We provide an unprecedented account of the chemical composition of roasted coffee beans. Using a targeted analytical approach we show for the first time, by comparison to authentic reference standards obtained by chemical synthesis, that chlorogenic acids follow four distinct reaction pathways including epimerization, acyl migration, lactonisation and dehydration. The analytical strategy employed in a non-targeted approach uses high resolution mass spectrometry to identify the most abundant molecular formulas present in roasted coffee samples and model roasts followed by van Krevelen and homologous series analysis. We identified the molecular formulas formed from reactions of chlorogenic acids, carbohydrates and proteins, both between classes of compounds and within same classes of compounds. Furthermore, we identified two new classes of compounds formed from chlorogenic acids during roasting, chlorogenic acid acetates and O-phenolic quinoyl and shikimoyl esters of chlorogenic acids.
咖啡是人类最受欢迎的饮料之一，由烘焙的绿咖啡豆制成。人们花费了大量精力来研究烘焙咖啡豆成分的化学特性，这些成分通常被称为类黑素，它们主要是由其最相关的次生代谢产物——绿原酸形成的副产物。然而，由于缺乏合适的真实参考标准和足够强大的分析技术来深入了解这种极其复杂的神秘物质，关于咖啡烘焙产物的结构和机制信息，令人惊讶地很少。在这里，我们使用目标和非靶向质谱技术的新概念组合，对烘焙咖啡的低分子量类黑素馏分进行了表征。我们提供了烘焙咖啡豆化学成分的空前描述。通过与通过化学合成获得的真实参考标准进行比较，我们使用靶向分析方法首次表明，绿原酸遵循包括差向异构化、酰基迁移、内酯化和脱水在内的四条不同反应途径。非靶向方法中使用的分析策略使用高分辨率质谱来鉴定存在于烘焙咖啡样品和模型烘焙物中的最丰富的分子公式，并进行范·克里夫伦（van Krevelen）和同源系列分析。我们鉴定了由绿原酸、碳水化合物和蛋白质之间的反应形成的分子公式，包括不同化合物类别的反应和同一化合物类别的反应。此外，我们还鉴定了在烘焙过程中由绿原酸形成的两类新化合物，即绿原酸乙酸酯和 O-酚醌酰基和莽草酸酯的绿原酸。
