VOLATILE COMPOUNDS IN FRESH AND PROCESSED ORIENTAL MUSHROOMS A thesis in the fulfilment of the requirements for the degree of Doctor of Philosophy by Lina Ashmore B. Sci Hons (Food Science and Technology, UNSW, Australia) B. Sci (Nutrition, University of Sydney, Australia) School of Chemical Engineering UNSW Sydney, NSW, Australia March 2014 ORIGINALITY STATEMENT ‘I hereby declare that this submission is my own work and to the best of my knowledge it contains no materials previously published or written by another person, or substantial proportions of material which have been accepted for the award of any other degree or diploma at UNSW or any other educational institution, except where due acknowledgement is made in the thesis. Any contribution made to the research by others, with whom I have worked at UNSW or elsewhere, is explicitly acknowledged in the thesis. I also declare that the intellectual content of this thesis is the product of my own work, except to the extent that assistance from others in the project's design and conception or in style, presentation and linguistic expression is acknowledged.’ Signed …………………………………………….............. 14 March 2014 Date …………………………………………….............. COPYRIGHT STATEMENT ‘I hereby grant the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or part in the University libraries in all forms of media, now or here after known, subject to the provisions of the Copyright Act 1968. I retain all proprietary rights, such as patent rights. I also retain the right to use in future works (such as articles or books) all or part of this thesis or dissertation. I also authorise University Microfilms to use the 350 word abstract of my thesis in Dissertation Abstract International (this is applicable to doctoral theses only). I have either used no substantial portions of copyright material in my thesis or I have obtained permission to use copyright material; where permission has not been granted I have applied/will apply for a partial restriction of the digital copy of my thesis or dissertation.' Signed ……………………………………………....................... 14 March 2014 Date …………………………………………….......................... AUTHENTICITY STATEMENT ‘I certify that the Library deposit digital copy is a direct equivalent of the final officially approved version of my thesis. No emendation of content has occurred and if there are any minor variations in formatting, they are the result of the conversion to digital format.’ Signed ……………………………………………....................... 14 March 2014 Date …………………………………………….......................... ACKNOWLEDGEMENT I would like to thank my supervisor Dr. George Srzednicki and my co-supervisor Dr. John D. Craske for their constant support and constructive guidance, endless encouragement throughout my PhD studies. The transmission of their precious and huge scientific knowledge about the aroma world accumulated during several years of research was of a considerable help for the development of this work. Avery special thanks for Dr. Noel Arrold from Li-Sun Exotic Mushrooms Ltd for his kindness and prompt supply of the exotic mushrooms. I would like to thank Camillo Taraborelli and Dr. Victor Wong who trained and assisted me in using equipment in the laboratory and provided help with instruments. Moreover, I wish to thank my friends from the school of Chemical Sciences for making this journey interesting. A special thanks to my colleague and friend Wiyanto Bie for his help and the pleasant work atmosphere throughout this entire journey and Dr. Veronica Chandra Hioe for her help and support. I would like to thank my dear friend Shereene for her friendship and for her unconditional support during the difficult times. At last, but not least, my heartfelt acknowledgements must go to my parents and siblings for their support and patience. I would have not been at this point without their encouragement and understanding. ii ABSTRACT Consumption of mushrooms is as old as the civilisation of people all over the world. The aroma is typical and special for each of the species of edible mushrooms. Despite their high consumption, only few studies were concerned with their aroma. This research aims at characterising the quality of the fresh and processed oriental mushrooms based on their aroma profile. As the volatile compounds (VC) are produced via metabolic and non- metabolic pathways, non-aggressive yet powerful techniques are needed to investigate their chemical composition. Their volatile profile has a potential to be used as quality control instrument useful for the industry. Ambient temperature vacuum distillation was successfully optimised to extract VC from fresh, boiled under reflux, dried at different temperatures (40, 50, 60, and 70 °C), and dried and boiled under reflux mushrooms samples. Four oriental mushroom species, Agrocybe aegerita (chestnut), Flammulina velutipes (enoki), Pleurotus ostreatus (oyster), and Lentinus edodes (shiitake) were studied. VC were identified by gas chromatography-mass spectrometry (GC-MS) using solid phase micro-extraction (SPME). A storage study of 10 days was also conducted in order to detect changes in VC in the different mushroom species in order to monitor their deterioration. The main C8 compounds present in all the studied mushrooms were decreasing over time while aldehydes ‘content was increasing. Furthermore, sulphur compounds in shiitake contributing to the overall deterioration of the aroma of fresh mushrooms were also increasing. The quality of dried materials depends on the physical and chemical changes occurring as a function of the processing conditions. Mushroom samples were dried at different temperatures to determine the most suitable one for aroma development. As for shiitake, 40 °C was chosen as the most suitable drying temperature while for chestnut 60 °C and for enoki and oyster 50 °C was the most appropriate. Some compounds such as limonene, furfuryl alcohol, 2-undecanone and some conjugated dienal in chestnut and oyster, pyrazine in enoki mushrooms, and lenthionine in shiitake were only generated via heat. Rehydration temperature played an important role in the liberation of VC. In general the maximum release of alcohols, aldehydes, pyrazine and conjugated diene from the dried material was higher at 100 °C rehydration temperature compared to 25 °C. The concentration of the main C8 compounds in chestnut, oyster mushrooms was decreasing when the dried samples were boiled under reflux as opposed to freshly boiled under reflux. In contrast, their concentrations iii in enoki and shiitake samples did not vary significantly. The qualitative and quantitative composition of the VC can be used as quality indicator and highlight the intensity of the processes in the studied mushrooms in the course of processing and storage. The knowledge of aroma profiles can assist in understanding of the mechanisms of the volatiles formation, generating desirable aromas or spoiling the product. Furthermore, the minimisation of degradation and deterioration of mushrooms during thermal processes requires the knowledge of the kinetics of degradation and process conditions. The outcome of this study is expected to provide a contribution to the science and also to the mushroom and food industry interested in formation and retention of pleasant aroma in fresh and processed mushrooms. iv TABLE OF CONTENTS ACKNOWLEDGEMENT .................................................................................................................................. II ABSTRACT ....................................................................................................................................................... III TABLE OF CONTENTS .................................................................................................................................... V ABBREVIATIONS ..........................................................................................................................................VIII LIST OF FIGURES ............................................................................................................................................ IX LIST OF TABLES ............................................................................................................................................ XV 1. INTRODUCTION ............................................................................................................................................ 1 1.1 PROBLEM STATEMENT ........................................................................................................................................ 1 1.2 BACKGROUND ................................................................................................................................................... 1 1.3 AIMS ............................................................................................................................................................... 2 1.3.1. Optimisation of vacuum distillation ............................................................................................. 2 1.3.2. Identification of volatile compounds by Gas chromatography-Mass spectrometry (GC-MS) using solid phase micro-extraction (SPME) .................................................................................................... 3 1.3.3. Detection of spoilage .................................................................................................................... 3 1.3.4.