COFFEE ROASTING: COLOR AND AROMA-ACTIVE SULFUR COMPOUNDS By ALBERTO MONTEIRO CORDEIRO DE AZEREDO A DISSERTATION PRESENTED TO THE GRADUATE SCHOOL OF THE UNIVERSITY OF FLORIDA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY UNIVERSITY OF FLORIDA 2011 1 © 2011 Alberto Monteiro Cordeiro de Azeredo 2 To God, for giving me the most caring wife, the most precious daughter, and the most supportive parents and family, who helped me in achieving this honorable milestone 3 ACKNOWLEDGMENTS I would like to give my deepest thanks to my advisors Dr. Balaban and Dr. Marshall for giving me this opportunity to pursue my PhD degree, and for their support, advice and friendship throughout this experience. Thanks to Dr. Rouseff for his invaluable help, assistance and time for my research, thanks for letting me be part of his lab. I also want to thank my other committee members, Dr. Sims and Dr. Welt, for all their expertise and help. I acknowledge all the assistance provided to me from the University of Florida, the Institute of Food and Agricultural Sciences, and the department of Food Science and Human Nutrition. I would also like to give my special thanks to Dr. Susan Percival for her continuous encouragement to pursue a PhD. I would like to thank Mr. Washington Rodrigues and Mr. Edgard Bressani from Ipanema Coffees, located in southern Minas Gerais, Brazil, for kindly providing green coffee beans for this research. I would like to thank my lab mates Milena and Maria for all their help and suggestions, and would like to extend my special thanks to Dr. Asli Odabasi and Lorenzo Fuentes for their time and expertise. Most of all, I thank my wife Gabriella, who gave me the strength to succeed and the support to accomplish my goals. I thank also my mom, Raquel, for her invaluable advices and most of all, for being an important influence in my life. For my daughter, Anna, who was born during my PhD program, and gave me extra enthusiasm to keep me going towards my goal. To my family in Brazil, I would like to give thanks for their encouragement. I thank my American parents, Shirley and Carl Romey, for their unconditional support and love. All of you made my moments in Gainesville the best time of my life. 4 TABLE OF CONTENTS page ACKNOWLEDGMENTS .................................................................................................. 4 LIST OF TABLES ............................................................................................................ 8 LIST OF ABBREVIATIONS ........................................................................................... 13 ABSTRACT ................................................................................................................... 15 CHAPTER 1 INTRODUCTION .................................................................................................... 17 Justification ............................................................................................................. 17 Objectives of Study ................................................................................................. 18 Specific Objectives.................................................................................................. 18 2 LITERATURE REVIEW .......................................................................................... 20 Coffee Origin and Market ........................................................................................ 20 Green Coffee Post-Harvest Processing .................................................................. 21 Dry or Natural Processing ................................................................................ 21 Wet Processing ................................................................................................ 22 Coffee Roasting ...................................................................................................... 23 General Aspects ............................................................................................... 23 The Process ..................................................................................................... 24 Heat and Mass Transfer ................................................................................... 24 Coffee Roasting Methods ................................................................................. 25 Rotating cylinder ........................................................................................ 25 Fixed drum with rotating paddles ............................................................... 26 Fluidized bed .............................................................................................. 26 Chemical Composition of Green and Roasted Coffees........................................... 27 Carbohydrates .................................................................................................. 27 Lipids ................................................................................................................ 27 Protein .............................................................................................................. 28 Alkaloids ........................................................................................................... 28 Chlorogenic Acids ............................................................................................ 29 Organic Acids ................................................................................................... 31 Physical Changes in Coffee during Roasting .......................................................... 32 Moisture............................................................................................................ 32 Surface and Structure of the Bean ................................................................... 32 Color ................................................................................................................. 33 Coffee Aroma and Flavor Development During Roasting ....................................... 34 Formation of Aroma Compounds ..................................................................... 36 Coffee Aroma Changes During Storage ........................................................... 37 5 3 COFFEE COLOR: KINETICS OF COLOR FORMATION DURING THE ROASTING PROCESS ........................................................................................... 52 Materials and Methods............................................................................................ 54 Sample Preparation .......................................................................................... 54 Color Analysis .................................................................................................. 55 Kinetic Considerations ...................................................................................... 56 L* values .................................................................................................... 57 a* and b* values ......................................................................................... 57 Statistical Analysis ............................................................................................ 58 Results .................................................................................................................... 58 Thermal Treatments ......................................................................................... 58 L* values........................................................................................................... 58 a* and b* values ............................................................................................... 60 Summary ................................................................................................................ 61 4 COMPARISON OF MINOLTA, HUNTERLAB AND MACHINE VISION IN ASSESSING THE COLOR OF ROASTED COFFEE AND THE AGTRON-SCAA ROAST COLOR CLASSIFICATION SYSTEM ........................................................ 73 Materials and Methods............................................................................................ 75 Agtron-SCAA Roast Color Classification System ............................................. 75 Coffee and Roaster Equipment ........................................................................ 76 Color Analysis .................................................................................................. 77 Sensory Analysis .............................................................................................. 79 Statistical Analysis ............................................................................................ 80 Results and Discussion........................................................................................... 80 Comparison of Color Measurement of the Agtron-RCCS with Different Instruments ................................................................................................... 80 Comparison of Color Measurement of Roasted Coffees Using Different Instruments ................................................................................................... 82 Correlation Between Sensory Analysis and Instrumental Measurements ........ 83 Summary ................................................................................................................ 86 5 COFFEE AROMA: FORMATION AROMA-ACTIVE SULFUR VOLATILES DURING COFFEE ROASTING .............................................................................. 97 Materials and Methods.........................................................................................