Understanding the Effects of Roasting on Antioxidant Components of Coffee Brews by Coupling On-line ABTS Assay to High Performance Size Exclusion Chromatography Sebastian E.W. Opitz, a Bernard A. Goodman, b Marco Keller, c Samo Smrke, a Marco Wellinger, a Stefan Schenker c and Chahan Yeretzian a * ABSTRACT: Introduction – Coffee is a widely consumed beverage containing antioxidant active compounds. During roasting the phytochem- ical composition of the coffee bean changes dramatically and highly polymeric substances are produced. Besides chlorogenic acids that are already present in green coffee beans, melanoidins show antioxidant capacity as well. Objective – To employ post-column derivatisation by coupling high performance size exclusion chromatography (HPSEC) to an antioxidant assay to investigate the effect of roasting on the properties of antioxidant active compounds in coffee brews. Methodology – We have investigated the antioxidant capacity of Coffea arabica (Arabica) and C. canephora (Robusta) beans that were roasted over the full spectrum of roast conditions (four roasting speeds to three roast degrees) by comparing the results from HPSEC coupled on-line to the ABTS assay with those from two batch assays, Folin Ciocalteu (FC) and oxygen radical absorbance capacity (ORAC) assay. Results – The antioxidant capacity showed a general decrease towards slower and darker roasted coffee for all three assays, indicative of heat degradation of active compounds. Hence, low molecular weight (LMW) compounds such as chlorogenic acids (CGAs) decreased progressively already from relatively mild roasting conditions. In contrast, high molecular weight (HMW) com- pounds (e.g. melanoidins) increased from light to dark roast degrees with lowering magnitude towards slower roasting profiles. Conclusion – By coupling HPSEC on-line to the ABTS assay we were able to separately quantify the contribution of HMW and LMW compounds to the total antioxidant capacity, increasing our understanding of the roast process. © 2016 The Authors. Phytochemical Analysis Published by John Wiley & Sons Ltd. Keywords: coffee; antioxidants; post-column derivatisation; HPSEC; Folin–Ciocalteu; ABTS •+ ; ORAC Introduction Coffee is a highly valued beverage and is primarily produced com- mercially by roasting green coffee beans from two species, Coffea arabica (Arabica) and C. canephora (Robusta). The consumption of coffee beverages has been linked to several beneficial health effects, partly because of the high content of phenolic substances (Scalbert et al., 2005; Ludwig et al., 2014). However, many studies on the effects of polyphenols on health have focussed on analyses of their antioxidant properties irrespective of their origin, although there is now growing evidence that their beneficial modes of action are not identical (Ludwig et al., 2014; Vicente et al., 2014). Nevertheless, (poly)-phenols, mostly of plant origin, have been commonly quantified collectively using one of the many antioxi- dant assays (Fraga et al., 2010; Lopez-Alarcon and Denicola, 2013). Green coffee beans contain large quantities of chlorogenic acids (CGAs), a family of water-soluble phenols formed by esterification of (À)-quinic acid with one or more cinnamic acids ( Jaiswal et al., 2014). However, besides CGAs, coffee possesses substantial quantities of other molecules that contribute to the total antioxi- dant capacity, e.g. melanoidins and various volatile compounds (Yu et al., 2013). The polymeric melanoidins are not present in green coffee, but are formed during the roasting process by Maillard and caramelisation reactions, and have been associated with both antioxidant properties and health benefits [for review see (Moreira et al., 2012)]. Whilst melanoidins are formed, the roasting process also results in the loss of some of the CGAs that are either degraded or partly incorporated in the melanoidins maintaining their antioxidant active catechol group (Perrone et al., 2012). Furthermore, other factors associated with coffee preparation, e.g. brewing conditions, such as time, temperature * Correspondence to: Chahan Yeretzian, Zurich University of Applied Sciences, Institute of Chemistry and Biotechnology, Einsiedlerstrasse 31, CH-8820 Wädenswil, Switzerland E-mail: yere@zhaw.ch a Zurich University of Applied Sciences, Institute of Chemistry and Biotechnol- ogy, Einsiedlerstrasse 31, CH-8820, Wädenswil, Switzerland b College of Physical Sciences and Technology, Guangxi University, Nanning 530004 Guangxi, China c Bühler AG, Gupfenstrasse 59240, Uzwil, Switzerland This is an open access article under the terms of the Creative Commons Attribution-NonCommercial-NoDerivs License, which permits use and distribu- tion in any medium, provided the original work is properly cited, the use is non-commercial and no modifications or adaptations are made. Phytochem. Anal. 2017, 28, 106–114 © 2016 The Authors. Phytochemical Analysis Published by John Wiley & Sons Ltd. Special Issue Article Received: 20 June 2016, Revised: 22 September 2016, Accepted: 11 October 2016 Published online in Wiley Online Library: 23 December 2016 (wileyonlinelibrary.com) DOI 10.1002/pca.2661 106