ADDIS ABABA UNIVERSITY ADDIS ABABA INSTITUTE OF TECHNOLOGY SCHOOL OF CHEMICAL AND BIO-ENGINEERING FOOD ENGINEERING PROGRAMME Effects of Coffee Roasting Technologies on Bioactive Compounds and Cup Quality of Specialty Coffee Beans Grown in Ethiopia A Thesis Submitted to the School of Chemical & Bio-Engineering in Partial Fulfillment of the Requirements for the Degree of Master of Science (M.Sc.) in Chemical Engineering (Food Engineering) By Muluken Zenebe Bolka November 7, 2019 Addis Ababa, Ethiopia Effects of Coffee Roasting Technologies on Bioactive Compounds and Cup Quality of Specialty Coffee Beans Grown in Ethiopia By Muluken Zenebe Bolka A Thesis Submitted in Partial Fulfillment of the Requirements for the Degree of Master of Science (M.Sc.) in Chemical Engineering (Food Engineering) School of Chemical and Bio-Engineering Addis Ababa Institute of Technology Addis Ababa University Advisor: Dr. Eng. Shimelis Admassu (Associate Professor) Title Page Copyright © Muluken Z. Bolka, 2019 i Declaration I, the undersigned, declare that this thesis presented for the attainment of the degree of Master of Science in Chemical Engineering (Food Engineering) has been composed solely by myself and has not been presented or submitted, in part or as a whole, for a degree in any other institution or university. The thesis presented is my original work and all sources of information or materials used for the thesis have been duly acknowledged. Mr. Muluken Zenebe Bolka Signature: _______________ Date: ___________________ M.Sc. Candidate This thesis has been submitted for examination with my approval and done under my supervision as University advisor. Dr. Eng. Shimelis Admassu Emire Signature: ______________ Date: ____________________ Advisor The undersigned members of the thesis examining board appointed to examine the thesis of Mr. Muluken Zenebe which is submitted for the degree of Master of Science in Chemical Engineering (Food Engineering) confirmed that the thesis fulfills the requirements of the graduate program and approved it to be accepted. Approved by the Examining Board: Signature Date _________________________________ _____________________ ___________________ Chairman, School’s Head Dr. Ing. Zebene Kifle _____________________ __________________ Internal Examiner Dr. Beteley Tekola _____________________ __________________ External Examiner ii Dedication I dedicate this thesis to my father for inspiring me as a young boy to have ambitious dreams. Thank you Ane! I have made it here with your inspiration. I also dedicate this thesis to my mother for teaching me what kind patience looks like in the face of tremendous obstacles. By your relentless prayers, I am here. I love you, Bayu! Additionally, I dedicate this work to my brothers, Tedla (Teddy), Zelalem (Oche), Tibebu (Abuye), and sister, Medhanit (Mimi). I am fortunate to be your brother. Finally, I dedicate this work to Bonna Coffee Processing for introducing me to my new found passion for “Coffee”. iii Acknowledgements First of all, I am so thankful to God for giving me the wisdom and strength to undertake and complete this study. Next, I am very grateful to my advisor, Dr. Eng. Shimelis Admassu for the confidence he had when he inspired me to undertake such an interesting and bold thesis dissertation title. His guidance and comments have were key to accomplish the research objectives. I am indebted to my sponsor Hawassa University and the School of Chemical and Bio Engineering, Addis Ababa University (AAU), for giving me the opportunity to pursue my graduate study. I would like to express my thanks to the managing director of Ethiopian Coffee and Tea Authority Coffee Quality Inspection and Certification Center (ECTACQICC), Mr. Berhanu Gezahegn for his kind permission to freely conduct the study at the center. His staffs at the coffee quality laboratory were very helpful, especially Mrs. Segenet, Mr. Seifedin and Mr. Tefera who shared their vast experience in coffee grading and sensory evaluation (cupping). I would like to also thank Mr. Taye and Mr. Agegnehu from Moyee Coffee PLC for allowing me to visit their company and use their roast analyzer device during their busy work time. My gratitude also goes to the staffs of Agricultural Quality Research Laboratory at the Ethiopian Institute of Agricultural Research (EIAR), especially Dr. Kassaye who granted me the permission to carry out part of my research in the institute’s laboratory. I would like to extend my special thanks from the bottom of my heart to Mr. Dinka Mulugeta for his priceless technical support when conducting the laboratory experiments at EIAR. Without him, this work may not have been possible. Last but not least, I would like to thank the staffs of EIAR at Wondogenet branch, especially Mr. Eyasu, Mr. Mulugeta and Mr. Bekri for their warm hospitality and technical support in finalizing my research. It remains for me to thank my family for their encouragements and love that in diverse ways made this study possible. I owe a special debt of gratitude to my uncle Mr. Asnake Bekele from whom I kindly obtained the samples for the study. Through him, I was able to access and get a hands on experience on the latest IKAWA® Pro roaster. A special thanks to the Aboneh’s family, Wondimagen’s family and Bonna Coffee Processing for making my stay in Addis enjoyable as always. I’m also grateful to Mr. Muluken Kebede and Mr. Woldeab Alemayehu for cheering me up throughout the entire journey. May God bless everyone who supported me during the study! iv Abstract The objective of this research was to study the effects of different type of coffee roasting technologies, namely Drum, Fluidized Bed and Traditional roasters on the cup quality and bioactive compounds of specialty coffee beans grown in Ethiopia. A total of 3 unwashed raw coffee varieties were selected for the study and collected from Yirgacheffe, Harar and Sidama coffee regions in Ethiopia. The sample coffee beans were specialty graded and roasted at light, medium & dark degree of roasts from 150°C - 200°C for 7 to 15 minutes. The roasted coffee beans were evaluated for cup quality at medium degree of roast by three professional cuppers. Next, the amount of caffeine, trigonelline and total chlorogenic acids present in each coffee samples were simultaneously analyzed using a high-performance liquid chromatography (HPLC). The amount of acrylamide formed in Yirgacheffe coffee during roasting was determined using UV-Visible Spectrophotometer. Based on cupping evaluation, traditional roaster resulted at the least total cup score for all the coffee varieties. Among other factors, only varietal difference and degree of roast were found to have significant (P < 0.05) effect on caffeine content of the sample coffee beans. Generally, a significant reduction in trigonelline and total chlorogenic acids content of the coffee beans was observed during roasting process, with darker roasts attaining the least values. A single analysis of variance on experimental results of acrylamide formation in roasted Yirgacheffe coffee showed significant (p < 0.05) differences for type of roaster and degree of roast. The highest acrylamide content, i.e. 2.303ppm was exhibited at light degree of roast using traditional roaster. Finally, drum roaster was found to be the best type of coffee roaster at medium degree of roast since it produced specialty coffee beans with the highest cup quality, optimum bioactive compounds content and minimum acrylamide formation at medium degree of roast. Keywords: Acrylamide, Bioactive Compounds, Cup Quality, Roaster, Specialty Coffee v T Table of Contents a Chapter Title Page № bl Title Page ......................................................................................................................................... i e Declaration ...................................................................................................................................... ii of Dedication ...................................................................................................................................... iii C Acknowledgements ........................................................................................................................ iv o Abstract ........................................................................................................................................... v n Table of Contents ........................................................................................................................... vi te List of Tables ............................................................................................................................... viii n List of Figures ................................................................................................................................ ix ts List of Abbreviations ...................................................................................................................... x List of Appendices ......................................................................................................................... xi 1. Introduction ........................................................................................................................... 1 1.1. Background ..................................................................................................................... 1 1.2. Statement of the problem .............................................................................................. 2 1.3. Research Question