Understanding the fate of chlorogenic acids in coffee roasting using mass spectrometry based targeted and non-targeted analytical strategies† Rakesh Jaiswal, a Marius F. Matei, a Agnieszka Golon, a Matthias Witt b and Nikolai Kuhnert * a Received 18th November 2011, Accepted 24th June 2012 DOI: 10.1039/c2fo10260a 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. Introduction Globally, coffee is following water and black tea as the third most consumed beverage with an annual production of around 8 Mt and an average daily consumption of 2.3 billion cups a day. 1 In several countries, such as the USA or Germany, it is even the second most consumed beverage. Coffee is obtained from the seeds of the cherries of Coffea arabica or Coffea conifera (otherwise known as Robusta coffee) referred to as green coffee beans. To obtain the popular beverage green coffee beans are roasted at temperatures ranging from 180  C to 250  C with roasting times ranging from 5 to 30 minutes, producing so called light to dark roasts. 2 While the volatile compounds formed in coffee roasting have been thoroughly investigated and studied, with so far around 800 distinct volatile compounds identified, including heterocycles such as pyrazines, furanethiols, disulfides and aldehydes, 3–7 the chemistry and structure of the non-volatile components of roasted coffee have only been investigated on few occasions and a dramatic lack of knowledge exists on this extraordinarily important dietary material, consumed at levels of several millions of tons annually. 2,8–10 The non-volatile products of coffee roast- ing are usually referred to as melanoidines, which have been shown by Schols and co-workers to be composed from several fractions of varying molecular weight that can be readily sepa- rated using dialysis. 2,8 Due to the complexity of the material it has been impossible to obtain useful structural information on the majority of the compounds formed in coffee roasting due to a lack of analytical techniques and strategies available to solve this enormously difficult task. Coffee melanoidines are formed in the roasting process from the main constituents of the green coffee beans which are chlorogenic acids, the main secondary plant metabolites of the green coffee bean, carbohydrates and proteins. Chlorogenic acids (CGAs) by definition are hydroxycinnamate esters of quinic acid with caffeic and ferulic acid being the most common substituents and 5-caffeoyl quinic acid 1 being the a School of Engineering and Science, Centre for Molecular Life Sciences, Jacobs University Bremen, Campusring 8, 28759 Bremen, Germany. E-mail: n.kuhnertx@jacobs-university.de; Tel: +49 421 2003120 b Bruker Daltonics, Fahrenheitstrasse 4, 28359 Bremen, Germany † Electronic supplementary information (ESI) available. See DOI: 10.1039/c2fo10260a This journal is ª The Royal Society of Chemistry 2012 Food Funct. Dynamic Article Links C < Food & Function Cite this: DOI: 10.1039/c2fo10260a www.rsc.org/foodfunction PAPER Downloaded by McGill University on 09 August 2012 Published on 26 July 2012 on http://pubs.rsc.org | doi:10.1039/C2FO10260A View Online / Journal Homepage