OPTIMIZATION OF BREWING, PROCESSING CONDITIONS AND THEIR EFFECTS ON THE CHEMICAL AND SENSORY QUALITY OF PURPLE-LEAFED KENYAN TEA EMILY CHERONO KILEL A Thesis Submitted to the Graduate School in Partial Fulfilment for the Requirements of the Doctor of Philosophy Degree in Food Science of Egerton University EGERTON UNIVERSITY NOVEMBER, 2019 DECLARATION AND RECOMMENDATION Declaration This thesis is my original work and has not, wholly or in parts, been presented for an award of a degree, in this or any other university. Signature ………………………………… Date: …………………………………………. Emily Cherono Kilel Reg. No.KD16/0458/14 Recommendation This thesis has been submitted with our approval as University supervisors: Signature ………………………………… Date: …………………………………………. Prof. Abdul Kipruto Faraj, Ph.D. Department of Dairy, Food Science and Technology, Egerton University, Njoro Signature ………………………………… Date: …………………………………… Dr. John Kanyiri Wanyoko, Ph.D. Formerly, Programme Leader, Tea Processing and Value Addition Programme, Kenya Agricultural and Livestock Research Organization (KALRO), Tea Research Institute (TRI), Kericho. Signature ………………………………… Date: …………………………………… Dr. Peninah Njiraine Ngoda, Ph.D. Department of Dairy, Food Science and Technology, Egerton University, Njoro. ii COPYRIGHT © 2019, Emily Cherono Kilel All rights reserved. Reproduction and dissemination of material in this thesis for educational or other non-commercial purposes are authorized without any prior written permission from the copyright holder provided the source is fully acknowledged. Reproduction of material in this thesis for resale or other commercial purposes is prohibited without written permission of the author or Egerton University. iii DEDICATION I dedicate this work to my family. iv ACKNOWLEDGEMENT I thank the Almighty God for his divine favour in this journey. I am indebted to Egerton University for giving me a chance to study and facilitating the whole process to completion. I salute the Tea Research Institute Director Dr. John Bore, for availing me an opportunity to conduct the research using the Institute‘s facilities. I acknowledge National Research Fund for awarding me research funds to partially support the study. I would like to recognise the financial support by Karatina University and the rare backing by the University management during the course of my study. I would like to thank my supervisors, Prof. Abdul Faraj, Dr. John Kanyiri Wanyoko, and Dr. Peninah Ngoda for their commitment in this work, their support, encouragement, knowledge and passion on the subject matter. The Tea Research Institute fraternity are highly appreciated for their support throughout the time when the research was being carried out. I acknowledge the tea tasters who facilitated the completion of this work, especially from the following tea factories; Kangaita, Nyansiongo, Nyankoba, Rionyamwamu, Kiamokama, Sanganyi, Nyamache and Gianchore. Mr. Vincent Mwingirwa and his team from KTDA Headquarters who tasted the green tea samples and their contribution are highly appreciated. Mr. Johnson Mwove, a cheerful good hearted man was resourceful in data analysis using SAS (Statistical Analysis Software), and his contribution is highly appreciated. Our Head of Department, in the Department of Food Science and Nutrition, Karatina University, Dr. Louise Ngugi and my dear colleagues have been part of this journey consistently and their contribution is cherished. I would like to thank my family members especially my husband Mr. Charles Bii, our sons Kelvy Kibet, Gim Saitira, Ken Kipkoech, Felix Kipruto, Marx Kiprono and my siblings especially Caleb Langat for their love, encouragement and support throughout my post graduate studies. To all those who supported and facilitated this research work in one way or another, your contribution is highly appreciated. v ABSTRACT The Tea Research Institute (TRI) developed TRFK 306 tea clone which is rich in anthocyanin as a strategy to diversify Kenyan teas. TRFK 6/8 was used as a control in the study being a standard clone used at the TRI. TRFK 306 can be utilized non-processed but there is no well researched, documented data on the best brewing conditions. Consumers add edible acids to its brew to improve the colour and taste but information on the acid effect is scanty. Information on the quality of products manufactured in various ways is equally scanty. Completely randomized block design replicated three times was adopted. Fresh TRFK 306 tea leaves were brewed using time temperature combinations of 70 0C and 92 0C timed at 5, 10 and 15 minutes prior to analysing for total anthocyanins and antioxidant activity. Citric acid concentration of 0.1 %, 0.2 %, 0.3 %, 0.4 % and 0.5 % were used to check their effect on total anthocyanins .antioxidant activity and sensory quality. Five- point hedonic scale was used in the sensory evaluation. Non-aerated and aerated orthodox and Crush, Tear and Curl (CTC) teas were processed at different withering times with an interval of 5 hours starting from 0 up to 20 hours. Aeration duration was varied at an interval of 30 minutes, from 30, to 90 minutes. Tea quality parameters were assayed using the Flavognost method, Roberts method, High Performance Liquid Chromatography (HPLC) and UV spectrophotometer. Experienced tea tasters tasted the processed samples subjectively. Data obtained were subjected to general linear model using SAS package version 9.1.3. Means were separated using Least Significant Difference at p < 0.05 significance level. Non- processed purple tea leaves brewed for five minutes using boiling water, had anthocyanins level of 92 mg/L and had over 87.7 % antioxidant activity without citric acid added. Citric acid lowered antioxidant activity though it improved the taste and colour. TRFK 306 non- aerated orthodox teas had more total catechins than CTC teas and best withered for 10-15 hours for higher antioxidant activity. Non- aerated TRFK 306 CTC teas had a score of 3.5 in liquor briskness while TRFK 6/8 teas highest scored was 2. Aerated TRFK 306 CTC teas had a highest theaflavins of 14.41 µmol/g compared to TRFK 6/8 CTC teas with highest value of 16.43 µmol/g. Aerated TRFK 306 orthodox teas had a highest liquor flavour score of 4 slightly lower than TRFK 6/8 orthodox teas with 4.4. It was concluded that, TRFK 306 can be utilized non-processed or can be processed into green orthodox or aerated CTC teas at withering hours not exceeding 15 hours and aeration time not exceeding 60 minutes for premium products. TRFK 306 tea leaves are recommended for direct use without much processing. vi TABLE OF CONTENTS DECLARATION AND RECOMMENDATION .................................................................. ii COPYRIGHT ......................................................................................................................... iii DEDICATION......................................................................................................................... iv ACKNOWLEDGEMENT ....................................................................................................... v ABSTRACT ............................................................................................................................. vi TABLE OF CONTENTS ...................................................................................................... vii LIST OF TABLES ................................................................................................................. xii LIST OF FIGURES ............................................................................................................. xiii LIST OF PLATES ................................................................................................................. xv LIST OF ABBREVIATIONS AND ACRONYMS ............................................................ xvi CHAPTER ONE ...................................................................................................................... 1 INTRODUCTION.................................................................................................................... 1 1.1 Background information .................................................................................................. 1 1.2 Statement of the problem ................................................................................................. 3 1.3 Objectives ........................................................................................................................ 4 1.3.1 General objective ...................................................................................................... 4 1.3.2 Specific objectives .................................................................................................... 4 1.4 Hypotheses ....................................................................................................................... 4 1.5 Justification ...................................................................................................................... 5 1.6 Scope and limitation ........................................................................................................ 5 1.7 Assumptions ..................................................................................................................... 6 1.8 Definition/description of terms ........................................................................................ 6 CHAPTER TWO ....................................................................................................................