MODULATION OF COFFEE AROMA VIA GREEN COFFEE BEAN FERMENTATION AND AROMA ENCAPSULATION WITH EMPHASIS ON COFFEE BEAN FERMENTATION LEE LIANG WEI WILSON NATIONAL UNIVERSITY OF SINGAPORE 2016 MODULATION OF COFFEE AROMA VIA GREEN COFFEE BEAN FERMENTATION AND AROMA ENCAPSULATION WITH EMPHASIS ON COFFEE BEAN FERMENTATION LEE LIANG WEI WILSON (B. Sc. (Hons.), Nanyang Technological University) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2016 THESIS DECLARATION I hereby declare that this thesis is my original work and it has been written by me in its entirety, under the supervision of Associate Professor Liu Shao Quan, (in the Food Science and Technology research laboratory S13-05), Chemistry Department, National University of Singapore, between August 2012 and August 2016. I have duly acknowledged all the sources of information which have been used in the thesis. This thesis has also not been submitted for any degree in any university previously. The content of the thesis has been partly published in: 1. Lee, L. W., Liu, X., Wong, W. S. E., & Liu, S. Q. (2017). Effects of sucrose monopalmitate (P90), Tween 80 and modified starch on coffee aroma retention and release in coffee oil-based emulsions. Food Hydrocolloids, 66, 128- 135. 2. Lee, L. W., Tay, G. Y., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2017). Modulation of the volatile and non-volatile profiles of coffee fermented with Yarrowia lipolytica: II. Roasted coffee. LWT - Food Science and Technology, 80, 32-42. i 3. Lee, L. W., Tay, G. Y., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2017). Modulation of the volatile and non-volatile profiles of coffee fermented with Yarrowia lipolytica: I. Green coffee. LWT - Food Science and Technology, 77, 225-232. 4. Lee, L. W., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2016). Modulation of coffee aroma via the fermentation of green coffee beans with Rhizopus oligosporus: II. Effects of different roast levels. Food Chemistry, 211, 925-936. 5. Lee, L. W., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2016). Modulation of coffee aroma via the fermentation of green coffee beans with Rhizopus oligosporus: I. Green coffee. Food Chemistry, 211, 916-924. 6. Lee, L. W., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2015). Coffee fermentation and flavor – An intricate and delicate relationship. Food Chemistry, 185, 182-191. Lee Liang Wei Wilson 19 August 2016 Name Signature Date ii ACKNOWLEDGEMENTS First and foremost, I would like to express my sincere gratitude to my supervisor Associate Professor Liu Shao Quan for his supervision and constant guidance throughout the entire project, without which this project would not have been as smooth-sailing. I would also like to thank him for giving me the opportunity to embark on a coffee project which is an area I am very interested in. From this doctoral program, I have truly benefited from his vast research experience and invaluable advice on both research project-related issues and future career directions. Secondly, I would like to thank the National University of Singapore, Firmenich Asia Pte Ltd., for providing the NUS-IPP scholarship and Compass Foods Pte Ltd., for providing the funding for the aroma encapsulation project that I have worked on. Thirdly, I would like to thank Dr Yu Bin and Dr Cheong Mun Wai for their guidance and inputs from their immense wealth of knowledge in coffee aroma and analytical methodologies. I would also like to thank my fellow seniors, Dr Lee Pin Rou Christine, Dr Sun Jingcan, Dr Li Xiao, Dr Chen Dai and Mr Satya Dwi Putra for helping me familiarize with the laboratory environment when I first joined the research group. I would like to thank my current laboratory group mates, Mr Toh Mingzhan, Mr Lu Yuyun, Ms Zhang Wencan, Ms Vong Weng Chan and Ms Wang Chenhui for their help and encouragement. I would also like to thank the technical staff of the FST department, Ms Lee Chooi Lan, Ms Lew iii Huey Lee, Ms Jiang Xiaohui and Mr Abdul Rahaman Bin Mohd Noor for their help in administrative and technical matters. Last but not least, I would like to thank my family and fiancée for their unwavering emotional support and encouragement since I started embarking on this journey. iv PUBLICATIONS LIST Publications derived from this thesis 1. Lee, L. W., Liu, X., Wong, W. S. E., & Liu, S. Q. (2017). Effects of sucrose monopalmitate (P90), Tween 80 and modified starch on coffee aroma retention and release in coffee oil-based emulsions. Food Hydrocolloids, 66, 128- 135. 2. Lee, L. W., Tay, G. Y., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2017). Modulation of the volatile and non-volatile profiles of coffee fermented with Yarrowia lipolytica: II. Roasted coffee. LWT - Food Science and Technology, 80, 32-42. 3. Lee, L. W., Tay, G. Y., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2017). Modulation of the volatile and non-volatile profiles of coffee fermented with Yarrowia lipolytica: I. Green coffee. LWT - Food Science and Technology, 77, 225-232. 4. Lee, L. W., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2016). Modulation of coffee aroma via the fermentation of green coffee beans with Rhizopus oligosporus: II. Effects of different roast levels. Food Chemistry, 211, 925-936. 5. Lee, L. W., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2016). Modulation of coffee aroma via the fermentation of green coffee beans with Rhizopus oligosporus: I. Green coffee. Food Chemistry, 211, 916-924. v 6. Lee, L. W., Cheong, M. W., Curran, P., Yu, B., & Liu, S. Q. (2015). Coffee fermentation and flavor – An intricate and delicate relationship. Food Chemistry, 185, 182-191. Other related publication 1. Sun, J., Lee, L. W. W., & Liu, S. Q. (2014). Biosynthesis of flavour- active esters via lipase-mediated reactions and mechanisms. Australian Journal of Chemistry, 67(10), 1373-1381. vi TABLE OF CONTENTS Page THESIS DECLARATION .................................................................................... i ACKNOWLEDGEMENTS ................................................................................ iii PUBLICATIONS LIST ........................................................................................ v SUMMARY ......................................................................................................... xii LIST OF TABLES .............................................................................................. xv LIST OF FIGURES ......................................................................................... xviii LIST OF ABBREVIATIONS ........................................................................... xix CHAPTER 1 INTRODUCTION ......................................................................... 1 1.1 COFFEE .......................................................................................................... 1 1.2 CONVENTIONAL AVENUES OF COFFEE AROMA MODULATION ......................... 1 1.3 POTENTIAL AVENUES OF COFFEE AROMA MODULATION ................................. 3 1.4 PROJECT OBJECTIVES ..................................................................................... 5 CHAPTER 2 LITERATURE REVIEW ............................................................. 8 2.1 FORMATION OF COFFEE AROMA ..................................................................... 8 2.1.1 Thermal degradation of aroma precursors.......................................... 12 2.1.2 Maillard reactions ............................................................................... 13 2.1.3 Relationship between the non-volatile profiles of green coffee and the aroma profiles of roasted coffee ................................................................... 15 2.2 POST-HARVEST COFFEE PROCESSING ............................................................ 16 2.2.1 Effects of processing methods on coffee aroma ................................... 18 2.3 FERMENTATION IN COFFEE PROCESSING ....................................................... 23 2.3.1 Microbiology of coffee fermentation .................................................... 24 2.3.2 Issues with coffee fermentation during wet-processing ....................... 25 2.3.3 Optimization of coffee fermentation..................................................... 27 2.4 NOVEL MEANS OF COFFEE AROMA MODULATION VIA FERMENTATION ......... 30 vii 2.5 INSTANT COFFEE AROMA .............................................................................. 35 2.6 AROMA ENCAPSULATION OF COFFEE OIL ...................................................... 37 CHAPTER 3 MODULATION OF COFFEE AROMA VIA THE FERMENTATION OF GREEN COFFEE BEANS WITH RHIZOPUS OLIGOSPORUS: I. GREEN COFFEE ............................................................. 39 3.1 INTRODUCTION............................................................................................. 39 3.2 MATERIALS AND METHODS .......................................................................... 41 3.2.1 Chemicals, reagents and solvents ........................................................ 41 3.2.2 Green coffee beans and R. oligosporus starter cultures ...................... 42 3.2.3. Solid-state fermentation (SSF) of green coffee beans ......................... 42 3.2.4 Volatile profile analysis ....................................................................... 43 3.2.5 Non-volatile profile analysis ................................................................ 44 3.2.5.1 Sample pre-treatment ...................................................................