Unravelling the Phenolic Composition and in Vitro Activities of Australian Native Mints
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Unravelling the Phenolic Composition and In vitro Activities of Australian Native Mints A thesis in fulfilment of the requirements for the degree of DOCTOR OF PHILOSOPHY By Kitty Sze Chiu Tang School of Chemical Engineering Faculty of Engineering March 2016 THE UNIVERSITY OF NEW SOUTH WALES Thesis/Dissertation Sheet Surname or Family name: Tang First name: Kitty Sze Chiu Other name/s: Abbreviation for degree as given in the University calendar: School: Chemical Engineering Faculty: Engineering Title: Unravelling the phenolic composition and in vitro biological activities of Australian native mints. Abstract Australia native flora has served as food and medicine for the indigenous people for thousands of years. However, systematic scientific investigation into their health properties is still in the early stage and rather limited in scope. In this thesis, the phenolic composition and in vitro biological activities of two native Australian mints – river mint (Mentha australis R. Br.) and mint bush (Prostanthera rotundifolia R. Br.) were systematically investigated for the first time. The phenolic compounds were extracted using 80% (v/v) aqueous methanol and purified by adsorbent material XAD-7 Amberlite® resin. The mint extracts were investigated for their phenolic composition, antioxidant capacity and inhibition towards key enzymes related to diabetes, obesity and inflammation (α-glucosidase, α-amylase, pancreatic lipase and hyaluroniase). The purified extracts were also analysed using state-of-the-arts analytical instruments, including high performance liquid chromatography in conjunction with various mass spectrometric methods and nuclear magnetic resonance spectroscopy, to identify and quantify the phenolic compounds in the mints. Overall, river mint possessed high total phenolic contents, free-radical scavenging and ferric reducing ability, and exhibited strong inhibitory effects on peroxyl radical-induced oxidation superior or comparable to most common herbs such as spearmint. Mint bush exhibited lower total phenolic contents and antioxidant capacities than the Mentha species, but the results were superior to many common herbs. The crude extracts of the Australian mints were stronger inhibitors of pancreatic lipase than the other enzymes. Furthermore, the polyphenolic-rich extracts of the mint herbs were also effective inhibitors of α-glucosidase. Major compounds identified in river mint were rosmarinic acid (30.4%), neoponcirin (29.5%), chlorogenic acid (7.7%), narirutin (5.6%), and biochanin A (1.9%) and trace amount of caffeic acid, apigenin, naringenin and hesperetin. Major phenolic compounds identified in mint bush were verbascoside (48.8%), 4-methoxycinnamic acid (36.4%), glucose ester of p-coumaric acid (9.2%) and 1-O-β-ᴅ-glucopyranosyl sinapate (5.6%), while minor compounds were caffeic acid, p-coumaric acid, hesperidin and naringenin. Significantly, neoponcirin and biochanin A were identified for the first time in the Mentha genus. Furthermore, 4-methoxycinnamic acid, glucose ester of p-coumaric acid and 1-O-β-ᴅ-glucopyranosyl sinapate were identified for the first time in the genus of Prostanthera. Declaration relating to disposition of project thesis/dissertation I hereby grant to the University of New South Wales or its agents the right to archive and to make available my thesis or dissertation in whole or in 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 property 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 Abstracts International (this is applicable to doctoral theses only). ………………………………………………… …………………………..……………… ……….……………………...…….… Signature Witness Signature Date The University recognises that there may be exceptional circumstances requiring restrictions on copying or conditions on use. Requests for restriction for a period of up to 2 years must be made in writing. Requests for a longer period of restriction may be considered in exceptional circumstances and require the approval of the Dean of Graduate Research. FOR OFFICE USE ONLY Date of completion of requirements for Award: i 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 ……………………………………………….. Date ……………………………………………….. ii 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 ……………………………………………........................... 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 ……………………………………………........................... Date ……………………………………………........................... iii ACKNOWLEDGEMENT I would like to express my sincere gratitude to my supervisor Associate Prof. Jian Zhao for his guidance, patience and immense knowledge. At times when my project is not going as smoothly as expected, he has always shown me the right direction. To Dr. Izabela Konczak, I would like to send my thanks for her encouragement and support. Thank you so much to both of them for their supervision and invaluable advice. I am grateful to Mr. Camillo Taraborreli for his continued technical assistance in the laboratory and Dr. Robert Chan for his IT support throughout my PhD. To Mr. Lewis Alder and Dr. Martin Bucknall from the Bioanalytical Mass Spectrometry Facility, and Dr. James Hook from the Nuclear Magnetic Resonance Facility – many thanks for providing expert advice with using analytical instruments. Lastly, I would like to thank to my family and friends, who have been with me throughout this journey, especially Ka Wai Fan for his endless support. iv LIST OF PUBLICATIONS AND PRESENTATIONS Tang, K. S., Konczak, I. & Zhao, J. (2016). Identification and quantification of phenolics in Australian native mint (Mentha australis R. Br.). Food Chemistry, 192, 698-705. Tang, K. S., Konczak, I. & Zhao, J. (2014). Phenolic identification of Australian native herbs and their antioxidant capacity. Presented at the XXVIIth International Conference on Polyphenols & the 8th Tannin Conference (ICP2014), Nagoya, Japan, 2-6 September 2014 – poster presentation. Tang, K. S. & Zhao, J. (2013). Antioxidant capacity and total phenolic content of three australian native plants. Presented at the Institute of Food Science and Technology 13th Annual Meeting & Food Expo, Chicago, USA, 13-16 July 2013 – poster presentation. v TABLE OF CONTENTS TABLE OF CONTENTS ................................................................................................ 1 LIST OF TABLES .......................................................................................................... 5 LIST OF FIGURES ........................................................................................................ 7 ABBREVIATIONS ....................................................................................................... 10 ABSTRACT ................................................................................................................... 12 CHAPTER 1 INTRODUCTION ................................................................................. 13 CHAPTER 2 LITERATURE REVIEW ..................................................................... 18 2.1. Introduction .......................................................................................................................... 18 2.2. Phytochemicals identified from Australian edible native plants ...................................... 21 2.2.1. Phenolic compounds ..............................................................................................................