Kinetics of volatile generation during coffee roasting and analysis using Selected Ion Flow Tube-Mass Spectrometry THESIS Presented in Partial Fulfillment of the Requirements for the Degree Master of Science in the Graduate School of The Ohio State University By Sangeetha Krishnaswamy Graduate Program in Food Science and Technology The Ohio State University 2017 Master's Examination Committee: Dennis R. Heldman, Advisor Sudhir Sastry Christopher Simons Copyrighted by Sangeetha Krishnaswamy 2017 Abstract Roasting is a critical step comprising of a series of complex reactions that are responsible for flavor generation in coffee. This study presents a real-time analytical technique that predicts the mechanism of volatile generations during different roasting conditions which could be ultimately used for online process control to deliver a more consistent target roast profile. The objectives of this research were to 1) To monitor the volatile compound generation during coffee roasting in real-time using online SIFT-MS 2) To investigate the influence of the time-temperature process during coffee roasting on the kinetics of volatiles generated and develop predictive models to determine kinetic parameters of volatile compounds and 3) predict temperature distribution histories within the coffee bean at different roasting conditions. Colombian Arabica coffee beans were roasted in a horizontal drum roaster at 210, 220 and 230 °C for 10, 15 and 20 minutes respectively. The concentrations of 7 volatile organic compounds (VOC’s), with impact on coffee flavor, were measured in the gas stream at the exit from the roaster using online Selected Ion Flow Mass Spectrometry (SIFT-MS) and were compared to the amounts retained in the final coffee extract. Modified Gompertz and Logistic models were used to describe the rate of volatile generation and estimate the kinetic parameters for the Volatile Organic Compounds (VOC’s) during different roasting conditions. The activation energy coefficients were calculated using the Arrhenius relationship. A transient heat conduction model for ii unsteady state heat transfer was used to determine the temperature distribution within the coffee bean. A synergy existed between the VOC release pattern in the roaster gas and the VOC formation/retention trend in the coffee extract. Excessive roasting (230 °C beyond 15 minutes), led to lower VOC concentrations in the roaster gas and the coffee extract. The modified Logistic models provided good statistical fit to the experimental data and precise estimation of kinetic parameters based on low NRMSE and SEE%. The changes in the temperature influenced the kinetics of volatile generation during the roasting process. The rate constant and peak concentration increased significantly with increase in temperature for all VOC’s. The range of activation energy coefficient for volatile compounds indicates a very high temperature sensitivity for the volatile compounds. The mass average temperature was predicted considering the mass contribution of different regions within the coffee bean using transient heat conduction model. Model validation was performed by combining the reference kinetics parameters of volatile compounds with the predicted mass average temperature. A correlation between the rate of volatile generation and the mass average temperature within the coffee bean was evident. The results showed that the predicted VOC concentration was in good agreement with the experimental values. The simulation can be useful for predicting VOC release for different roaster types and optimizing the roasting conditions. iii Acknowledgments I would like to sincerely express my gratitude to my advisor, Dr. Dennis R. Heldman and to my committee members Dr. Sudhir Sastry and Dr. Christopher Simons. I would like to thank David Phinney for helping me with the experimental setup. Finally, I would like to thank my parents and my husband for their support and encouragement throughout my education. iv Vita 2006-2010 ......................................................B Tech. Chemical Engineering, Anna University 2015-present ...................................................M.S. Department of Food Science and Technology, The Ohio State University Fields of Study Major Field: Food Science and Technology v Table of Contents Abstract ............................................................................................................................... ii Acknowledgments.............................................................................................................. iv Vita ...................................................................................................................................... v List of Tables ..................................................................................................................... xi List of Figures .................................................................................................................. xiii Chapter 1: Introduction ....................................................................................................... 1 References ....................................................................................................................... 5 Chapter 2: Literature Review .............................................................................................. 6 2.1 Green bean constituents ............................................................................................ 6 2.2 Coffee Roasting ......................................................................................................... 7 2.2.1 Background ......................................................................................................... 7 2.2.2 Roasting Process ................................................................................................. 7 2.2.3 Roasting Equipment ........................................................................................... 8 2.2.4 Heat and Mass transfer inside the coffee bean during roasting .......................... 8 2.2.5 Physical changes during roasting ..................................................................... 10 vi 2.2.6 Volatiles of Roasted Coffee .............................................................................. 11 2.2.7 Mechanism of Volatile generation ................................................................... 16 2.2.8 Changes in coffee aroma profile during storage ............................................... 17 2.3 Analytical measuring techniques ............................................................................ 19 2.3.1 Gas Chromatography ........................................................................................ 19 2.3.2 Proton Transfer Reaction- Mass Spectrometry (PTR-MS) .............................. 19 2.3.3 Selective Ion Flow Tube-Mass Spectrometry .................................................. 20 2.4 Non-linear curve fitting models .............................................................................. 25 References ..................................................................................................................... 27 Chapter 3: Real-time analysis of volatiles during coffee roasting using Selected Ion Flow Tube-Mass Spectrometry .................................................................................................. 33 Abstract ......................................................................................................................... 33 3.1 Introduction ............................................................................................................. 35 3.2 Materials and Methods ............................................................................................ 40 3.2.1 Roasting Procedure ........................................................................................... 40 3.2.2 SIFT-MS method development ........................................................................ 40 3.2.3 SIFT-MS Roaster Gas Analysis ....................................................................... 41 3.2.4 SIFT-MS coffee brew analysis ......................................................................... 43 3.2.5 Gaussian function ............................................................................................. 44 vii 3.2.6 Statistical analysis............................................................................................. 44 3.3 Results and Discussion ............................................................................................ 45 3.3.1 VOC release from the roaster ........................................................................... 45 3.3.2 VOC formation in coffee extract ...................................................................... 47 3.3.3 Comparison of VOC generation during roasting and from coffee extract ....... 49 3.3.4 Gaussian function ............................................................................................. 50 3.3.5 Comparison of VOC parameters ...................................................................... 53 3.4 Conclusion ............................................................................................................... 55 References ..................................................................................................................... 56 Chapter 4: Kinetic parameters for volatiles generated during coffee roasting ................. 58 Abstract ........................................................................................................................