The Compositional Basis of Coffee Flavour Wenny Bekti Sunarharum Bachelor of Agricultural Technology (STP) Master of Food Studies (MFoodSt) A thesis submitted for the degree of Doctor of Philosophy at The University of Queensland in 2016 Queensland Alliance for Agriculture & Food Innovation (QAAFI) Abstract Coffee trade is a billion-dollar industry and coffee remains one of the most traded commodities of economic importance to both the countries producing, and the countries consuming coffee. To ensure demand, it is of great importance to constantly maintain and, where possible, improve its quality. Flavour is crucial to coffee quality. However, describing coffee flavour is a very complex task as it is influenced by numerous factors from the farm to cup. These factors influence compositional properties of coffee and have a large impact on the perceived flavour. The ultimate aim of this project was to understand how different components in coffee influence flavour perception. The approach involved an exploration on the sensory and physicochemical profiles of sensorily diverse 26 commercial single-origin ‘specialty’ coffees. Sensory evaluation of these 26 selected coffees involves assessment on the brews while coffee ground and extracts were analysed for physicochemical profiles. An analytical method was developed and applied for rapid quantification of the targeted volatiles compounds in coffee. The results of sensory and physicochemical evaluation were modelled using a multivariate analysis to explore the relationship between attributes and to know potential sensory markers that could contribute to coffee flavour. Coffee proved to be a highly challenging matrix to study and required special preparation and presentation of individual samples at consistent temperature during sensory evaluation. Nevertheless, sensory profiles for the diverse range of coffees was achieved. Certain coffees were clearly distinctive: Ethiopian coffees registered fruity, citrus and aromatic spice sensory profile notes, Australian coffees exhibited milder profiles, while India Robusta coffees generally possess smoky, woody, earthy and cereals profile. Three analytical stable isotope dilution analysis/gas chromatography-mass spectrometry (SIDA/GC-MS) methods were developed and applied to quantify 27 key volatile compounds which were targeted due to their reported importance to coffee flavour. These methods involved a headspace-solid phase microextraction/gas-chromatography (HS- SPME/GC-MS) of coffee, steam distillation extraction of coffee followed by a HS- SPME/GC-MS and direct liquid injection of a steam distilled extract of coffee to GC-MS. i The 26 medium-roasted single-origin coffees investigated were quite diverse in physicochemical properties. It was clear that some coffees showed distinct physicochemical characters, for example, Robusta coffee contained doubled the caffeine content, higher concentrations of dicaffeoylquinic acids (diCQAs), higher pH, and higher L* value (a measure of lightness) but was lower in crude fat and trigonelline than the Arabica coffees. Principal component analysis (PCA) and partial least squares (PLS) regression were used as multivariate modelling techniques using compositional variables to mathematically predict coffee sensory attributes scoring. The models could be validated (Rv2≥0.4) for sensory attributes: aroma intensity, citrus, earthy, sourness, bitterness, flavour intensity and residual. For example: the prediction of sourness using caffeic acid, titratable acidity (TA), L* value and pyrazines; the prediction of citrus using ketones and aldehydes. The results indicated that those chemical components could be potential and contribute to certain sensory attributes of coffee. An additional study was conducted on the evolution of important chlorogenic acids from the green coffee beans to the coffee brews and to know the potential role to coffee flavour, specifically to volatile phenols. Chlorogenic acids were progressively lost during coffee processing with approximately only a fifth of the level in green coffee beans remains in a cup of coffee. The evolution of chlorogenic acids during coffee processing involves biochemical degradation and synthesis pathway that include acyl migration, isomerisation, lactonisation, epimerisation, hydrolysis, and polymerisation mechanism. Since there was no relationship found between the volatile phenols and chlorogenic acids, further investigation on the contribution of chlorogenic acids to coffee flavour will be beneficial. Since not all important components of coffee have been measured in this study, not every predictive model performed well. However, this is the first study to investigate sensory and physiochemical properties of a broad range of commercially diverse single-origin ‘specialty’ coffees as well as to quantify volatile monoterpenes especially geraniol. This study provided a new knowledge on an Australian coffees and specific coffee types such as Indonesia Luwak (Arabica) and Indian Monsooned Malabar. The present study also provides some interesting insight on coffee flavour. It has shown the potential for further coffee and flavour researches while offering advantages for industrial applications. ii Declaration by author This thesis is composed of my original work, and contains no material previously published or written by another person except where due reference has been made in the text. I have clearly stated the contribution by others to jointly-authored works that I have included in my thesis. I have clearly stated the contribution of others to my thesis as a whole, including statistical assistance, survey design, data analysis, significant technical procedures, professional editorial advice, and any other original research work used or reported in my thesis. The content of my thesis is the result of work I have carried out since the commencement of my research higher degree candidature and does not include a substantial part of work that has been submitted to qualify for the award of any other degree or diploma in any university or other tertiary institution. I have clearly stated which parts of my thesis, if any, have been submitted to qualify for another award. I acknowledge that an electronic copy of my thesis must be lodged with the University Library and, subject to the policy and procedures of The University of Queensland, the thesis be made available for research and study in accordance with the Copyright Act 1968 unless a period of embargo has been approved by the Dean of the Graduate School. I acknowledge that copyright of all material contained in my thesis resides with the copyright holder(s) of that material. Where appropriate I have obtained copyright permission from the copyright holder to reproduce material in this thesis. iii Publications during candidature Peer-reviewed journal and poster publications: Sunarharum, W.B.; Williams, D.J.; Smyth, H.E. 2014. Complexity of coffee flavour: A compositional and sensory perspective. Food Research International 62: 315–325 (Review article). Sunarharum, W.B.; Williams, D.J.; Smyth, H.E. 2013. Sensory profiling of coffee from around the world (poster: 46th Annual AIFST Convention, Brisbane, Australia July 14-16 2013 and QAAFI’s annual research meeting (ARM), Redcliffe, Australia on 6-7 August 2013). Sunarharum, W.B.; Mayze, J.; Williams, D.J.; Fox, G.; Smyth, H.E. 2014. Sensory Properties of Coffee from Different Geographical Origins (poster, World Food Day competition, The University of Queensland, Australia, 16 October 2014 and QAAFI’s annual research meeting (ARM), Brisbane, Australia on 25 November 2013). The aroma of commercial single-origin coffees from around the world (3rd International Congress on Cocoa Coffee and Tea, 22-24 June 2015, University of Aveiro, Portugal 2015). Exploring 26 single-origin coffees based on non-volatile composition (Tropical Agriculture Conference, TropAg 2015, 16-17 November, Brisbane, Australia). Oral presentations at conferences, seminars and competitions: Sensory profiling of coffee from around the world (student oral presentation competition at 46th Annual AIFST Convention, Brisbane July 14-16 2013). Investigation of chlorogenic acids and caffeic acid content on a range of green, roasted, and brewed Arabica coffee (2014 AIFST Food Science Summer School, Brisbane, 5-7 February 2014). Why coffee tastes good (National Science Week, Health & Food Science Precinct, 16-24 August 2014). Why coffee smells good (3MT-QAAFI-UQ Competition, July 2015). iv Publications included in this thesis Sunarharum, W.B.; Williams, D.J.; Smyth, H.E. 2014. Complexity of coffee flavour: A compositional and sensory perspective. Food Research International 62: 315–325 (Review article) – incorporated as Chapter 1 (p.1) and Chapter 2 (p.5). Contributor Statement of contribution Wenny B. Sunarharum (Candidate) Wrote and reviewed paper (90%) Edited paper (65%) Heather E. Smyth Wrote and reviewed paper (10%) Edited paper (30%) David J. Williams Edited paper (5%) v Contributions by others to the thesis Contributor Statement of contribution Australian Research Council Supporting project through ARC Linkage project funding scheme (project number LP130100376). Green Cauldron Coffee Australia, Providing commercial coffee samples. Carlini Coffee Company Australia, Kopi Luwak Nusantara Indonesia Heather Smyth (Principal Advisor, Designing the ultimate coffee project. Providing QAAFI) guidance in designing and conducting most of the experiments. Facilitating and providing assistance on data analysis