Chemical Components and Aromatic Profiles of Citrus
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CHEMICAL COMPONENTS AND AROMATIC PROFILES OF CITRUS AND COFFEE IN ASIA CHEONG MUN WAI NATIONAL UNIVERSITY OF SINGAPORE 2013 CHEMICAL COMPONENTS AND AROMATIC PROFILES OF CITRUS AND COFFEE IN ASIA CHEONG MUN WAI (B. Tech. (Hons.), MSc., Universiti Sains Malaysia) A THESIS SUBMITTED FOR THE DEGREE OF DOCTOR OF PHILOSOPHY DEPARTMENT OF CHEMISTRY NATIONAL UNIVERSITY OF SINGAPORE 2013 ACKNOWLEDGEMENTS This study would not have been completed without the constant support from many people who have helped me through this challenging period of my life. Gratitude must first go to my supervisor, Asst. Prof. Dr. Liu Shao Quan for entrusting this collaboration project to me; and for his advice and support throughout my study. Special thanks must also be made for the influence of my co-supervisor, Dr. Yu Bin, a truly creative and talented scientist, and a mentor for many lessons in life. Other outstanding characters I had had the fortune of learning from includes Prof. Zhou Weibiao who gave me valuable and constructive comments. Amongst many other sources of motivation and inspiration too numerous to be mentioned, the flavor creation team of Firmenich Asia Pte. Ltd. deserves special mention for their enthusiastic support of the whole project. I am very grateful to Mr. Philip Curran for having the foresight to commence this project; Mr. Kiki Pramudya who has volunteered himself in the sampling expeditions; Ms. Yeo Jinny, Ms. Chionh Hwee Khim and Ms. Yukiko Ando Ovesen for their time and effort. Special thanks, also, to my comrades, Weng Wai, Shen Siung, Jing Can, Christine, Li Xiao, Li Jie, Xiu Qing, Jingting, Zhi Soon, Danping, Jia Xin, Alena, Jeremy, Justin, Sheng Jie, for their contributions to all aspects of my work as well as other aspects of my life. i In addition, a huge thank you to the FST laboratory staff – Ms. Lee Chooi Lan, Ms. Lew Huey Lee, Ms. Jiang Xiao Hui and Mr. Abdul Rahman who, have always been instrumental in helping me with my experiments. I am deeply indebted to my family for their endless love and encouragements that allowed me to pursue my dream without fear. Last but not least, I would like to thank the National University of Singapore for granting the research scholarship. ii TABLE OF CONTENTS ACKNOWLEDGEMENTS i TABLE OF CONTENTS iii SUMMARY x LIST OF TABLES xii LIST OF FIGURES xiv LIST OF ABBREVIATIONS xvi LIST OF PUBLICATIONS xvii CHAPTER 1 Introduction and Literature Review 1 1.1. Background 1 1.2. Recent developments of flavor science 3 1.2.1. The search for novel flavor compounds 4 1.2.2. Biogenesis of fruit aroma 6 1.2.3. Thermal generation of flavors 7 1.2.4. Flavor release in complex food systems 8 1.3. Flavor isolation techniques 9 1.3.1. Solvent extraction techniques 10 1.3.2. Sorptive extraction techniques 13 1.4. Instrumental methods of flavor analysis 15 1.4.1. Chromatographic techniques 16 1.4.2. Gas chromatography-olfactometry 17 1.4.3. Mass spectrometric techniques 19 1.5. Sensory evaluation 20 1.6. Statistical analysis 22 iii 1.7. Exploration of authentic and indigenous citrus and coffee flavors in Asia 24 1.7.1. Pomelo (Citrus grandis (L.) Osbeck) and calamansi (Citrus microcarpa) 24 1.7.2. Arabica coffee in Asia 27 1.8. Objectives and research outline 30 1.9. Thesis outline 31 CHAPTER 2 Characterization of Volatile Compounds and Aroma Profiles of Malaysian Pomelo (Citrus grandis (L.) Osbeck) Blossom and Peel 33 2.1. Introduction 33 2.2. Experimental procedures 34 2.2.1. Pomelo materials 34 2.2.2. HS-SPME sampling procedure 35 2.2.3. GC-MS analysis 36 2.2.4. Sensory evaluation 36 2.3. Results and discussion 37 2.3.1. Volatile composition of pomelo blossoms 37 2.3.2. Volatile composition of pomelo peels 42 2.3.3. Sensory evaluation 46 2.4. Conclusion 47 CHAPTER 3 Identification of Aroma-Active Compounds in Malaysian Pomelo (Citrus grandis (L.) Osbeck) Peel by Gas Chromatography- Olfactometry 48 3.1. Introduction 48 3.2. Experimental procedures 49 3.2.1. Preparation of pomelo peel extracts 49 3.2.2. GC-MS/FID analysis 50 3.2.3. Sensory evaluation 50 3.2.4. Gas chromatography-olfactometry (GC-O) 51 3.2.5. Aroma model 52 iv 3.3. Results and discussion 52 3.3.1. Volatile composition of pomelo peel extracts 52 3.4. Conclusion 67 CHAPTER 4 Chemical Composition and Sensory Profile of Pomelo (Citrus grandis (L.) Osbeck) Juice 68 4.1. Introduction 68 4.2. Experimental procedures 69 4.2.1. Chemicals 69 4.2.2. Preparation of pomelo juice 70 4.2.3. Extraction of volatile compounds using HS-SPME 70 4.2.4. Extraction of volatile compounds using organic solvents 71 4.2.5. GC-MS/FID analysis 72 4.2.6. Physicochemical properties 72 4.2.7. Ultra-fast liquid chromatography (UFLC) instrumentation 72 4.2.7.1 HPLC analysis of sugars 73 4.2.7.2 HPLC analysis of organic acids 73 4.2.8. Sensory evaluation 74 4.2.9. Statistical analysis 74 4.3. Results and discussion 75 4.3.1. Volatile composition of pomelo juices 75 4.3.2. Physicochemical properties and non-volatile composition of pomelo juices 80 4.3.3. Sensory evaluation and correlation with instrumental data using multivariate analysis 82 4.4. Conclusion 88 CHAPTER 5 Characterization of Calamansi (Citrus microcarpa): Volatiles, Aromatic Profile and Phenolic Acids in the Peels 89 5.1. Introduction 89 5.2. Experimental procedures 90 v 5.2.1. Calamansi materials and chemicals 90 5.2.2. Extraction of volatile compounds 91 5.2.3. GC-MS/FID analysis 91 5.2.4. Extraction of phenolic acids 92 5.2.5. UFLC/PDA analysis of phenolic acid content 93 5.2.6. Statistical analysis 93 5.2.7. Sensory evaluation 94 5.3. Results and discussion 95 5.3.1. Volatile components of calamansi peel 95 5.3.2. Statistical analysis 101 5.3.3. Sensory evaluation 107 5.3.4. Phenolic acid content 109 5.4. Conclusion 111 CHAPTER 6 Characterization of Calamansi (Citrus microcarpa): Volatiles, Physicochemical Properties and Non-volatiles in the Juice 112 6.1. Introduction 112 6.2. Experimental procedures 114 6.2.1. Calamansi materials and chemicals 114 6.2.2. Solvent extraction of volatiles 115 6.2.3. Headspace-solid phase microextraction (HS-SPME) 115 6.2.4. GC-MS/FID analysis 115 6.2.5. Physicochemical properties 116 6.2.6. Extraction of phenolic acids 116 6.2.7. Ultra-fast liquid chromatography (UFLC) analysis 117 6.2.8. Statistical analysis 117 6.3. Results and discussion 118 6.3.1. Volatile components of calamansi juice 118 6.3.2. Physicochemical properties of calamansi juice 123 6.3.3. Sugar content of calamansi juice 124 6.3.4. Organic acid content of calamansi juice 125 vi 6.3.5. Phenolic acid content of calamansi juice 126 6.3.6. Principal component analysis (PCA) 128 6.4. Conclusion 131 CHAPTER 7 Simultaneous Quantitation of Volatile Compounds in Citrus Beverage through Stir Bar Sorptive Extraction Coupled with Thermal Desorption-Programmed Temperature Vaporization 132 7.1. Introduction 132 7.2. Experimental procedures 134 7.2.1. Materials and sample preparation 134 7.2.2. SBSE procedure 138 7.2.3. Analytical procedure 138 7.2.4. Optimization of TD-PTV injection process 139 7.2.5. Partial factorial design for SBSE extraction 141 7.2.6. Model evaluation and validation on model citrus beverage 142 7.3. Results and discussion 143 7.3.1. Optimisation of TD-PTV injection process 143 7.3.2. Understanding of SBSE extraction 149 7.3.3. Method evaluation and validation 153 7.3.4. Matrix effect of model citrus beverage on SBSE extraction 154 7.4. Conclusion 157 CHAPTER 8 Volatile Composition and Antioxidant Capacity of Arabica Coffee 158 8.1. Introduction 158 8.2. Experimental procedures 159 8.2.1. Coffee beans and chemicals 159 8.2.2. Preparation of coffee extracts 160 8.2.2.1 Extraction of volatile compounds 160 8.2.2.2 Extraction of phenolic acids 161 8.2.3. Instrumental analysis 161 vii 8.2.3.1 GC-MS/FID analysis 161 8.2.3.2 UFLC/PDA analysis 162 8.2.4. Determination of total polyphenol content 162 8.2.5. Determination of antioxidant activity 163 8.2.5.1 DPPH assay 163 8.2.5.2 FRAP assay 163 8.2.6. Statistical analysis 164 8.2.7. Sensory evaluation 164 8.3. Results and discussion 165 8.3.1. Volatile composition 165 8.3.2. Principal component analysis (PCA) 170 8.3.3. Phenolic acid components 173 8.3.4. Antioxidant activity 174 8.3.4.1 Determination of total polyphenol content 174 8.3.4.2 Radical scavenging activity by DPPH assay 175 8.3.4.3 Ferric reducing antioxidant power by FRAP assay 176 8.3.5. Sensory evaluation 177 8.4. Conclusion 179 CHAPTER 9 Pressurized Liquid Extraction on Coffee Bean 180 9.1. Introduction 180 9.2. Experimental procedures 181 9.2.1. Coffee beans and chemicals 181 9.2.2. PLE procedure 182 9.2.3. Solvent extraction 183 9.2.4. GC-MS/FID analysis 183 9.2.5. RSM and statistical analysis 183 9.2.6. Optimization and validation procedures 184 9.2.7. Sensory evaluation 185 9.3. Results and discussion 185 viii 9.3.1. Selection of extraction solvent, ratio of hydromatrix to sample and extraction cycle 186 9.3.2. Face-centered central composite design 189 9.3.2.1 Effect of PLE operating parameters 190 9.3.2.2 Interaction between PLE operating variables 193 9.3.2.3 Optimization of PLE operating variables 196 9.3.2.4 Validation of response surface model 197 9.3.3.