Assessment of Levels of Monosodium Glutamate, Aspartame and Sodium Benzoate in Some Chili and Tomato Sauces in Nairobi County, Kenya
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ASSESSMENT OF LEVELS OF MONOSODIUM GLUTAMATE, ASPARTAME AND SODIUM BENZOATE IN SOME CHILI AND TOMATO SAUCES IN NAIROBI COUNTY, KENYA Elizabeth Waithira Oyiengo (BSc.) Reg/ No. I56/24613/2011 A thesis submitted in partial fulfillment of the requirements for the award of the Degree of Master of Science (Applied Analytical Chemistry) in the School of Pure and Applied Sciences of Kenyatta University NOVEMBER 2014 ii DECLARATION I hereby declare that this is my original work and has not been presented for the award of a degree in any other university. Elizabeth Waithira Oyiengo (BSc.) Chemistry Department Kenyatta University Signature ………………….. Date…………….. This thesis has been submitted with our approval as University supervisors. Prof. Jane Igoki Murungi Chemistry Department Kenyatta University Signature ………………….. Date ……………. Dr. Ruth Nduta Wanjau Chemistry Department Kenyatta University Signature…………………... Date ……………. iii DEDICATION I dedicate this work to my dear husband Calleb Oyiengo and our children John, Joshua and Japheth. iv ACKNOWLEDGEMENTS I wish to express my gratitude to all those who assisted me in one way or another to make this work successful. I am grateful to God for His grace and strength during the study period. My sincere thanks go to my supervisors, Prof. Jane Murungi and Dr. Ruth Wanjau for their exemplary guidance, suggestions and encouragement throughout the period of my study. I am so grateful to the staff of Government Chemist Department for their moral support and particularly to Mr. Lawrence Waweru for allowing me to do my research work in the Department. I also wish to thank Rose Sikuku, Geoffrey Anyona, Alexander Mbaye, Hezron Onyangore and Margaret Maina for their guidance during laboratory analysis. Special thanks also go to Eunice Wamuyu, John Kibuthi and Hudson Nyambunde for assisting in purchasing the chemicals. I thank the technical staff of Chemistry Department; Kenyatta University, specifically Mr. Denis Osoro for guiding me in data analysis. I finally thank my family particularly my husband Calleb for his moral and material support throughout the period of my study, and who together with our children missed my presence during the study period. May the almighty God bless each and every one of you, Amen. v TABLE OF CONTENTS TITLE PAGE………………………………………………………………………………i DECLARATION……………………………………………………………………….…ii DEDICATION…………………………………………………........................................iii ACKNOWLEDGEMENTS……………………………………………………..………..iv TABLE OF CONTENTS……………………………………………………………….....v LIST OF TABLES…………………………………………………………………….......x LIST OF FIGURES……………………………………………………………………...xii LIST OF PLATES…………………………………………………………………...….xiii ABBREVIATION AND ACROYNMS……………………………...............................xiv ABSTRACT………………………………………………..………………………….....xv CHAPTER ONE………………………………………………………………………....1 INTRODUCTION…………………………………………………………………….....1 1.1 Background…………………………………………………………………………....1 1.2 Problem statement and justification…………………………………………………...3 1.3 Hypotheses………………………………………………………………………...…..5 1.4 Research question…………………………………………………………..................5 1.5 Objectives…………………………………………………………………………......5 1.5.1 Main objective…………………………………………………………………...….5 1.5.2 Specific objective……………………………………………………………………5 1.6 Significance of the study…………………………………………………….………...6 vi 1.7 Scope and limitations...………………………………………………………………..6 CHAPTER TWO…………………………………………………………..…………….7 LITERATURE REVIEW………..……………………………………………..……….7 2.1 Food additives…………………………………………………………………………7 2.2 Food additives and health……...……………………………………………………...8 2.2.1 Monosodium glutamate……………………………………………………………..9 2.2.2 Aspartame………………………………………………………………………….10 2.2.3 Sodium benzoate…………………………………………………………………...11 2.3 Chili and tomato sauce…………………………………………………………….....12 2.3.1 Chili sauce………………………………………………………………………….13 2.3.2 Tomato sauce………………………………………………………………………14 2.4 Method of analysis…………………………………………………………………...15 2.5 High performance liquid chromatography (HPLC)…………...……………………..15 CHAPTER THREE………………………………………………………………...…..17 RESEARCH METHODOLOGY……………..……………………………………….17 3.1 Research design………………………………………………………………...........17 3.2 Sampling and sample pre-treatment…………………………………………..……...17 3.3 Cleaning of glassware ……………..…………………………………...…………....18 3.4 Solvents and reagents………………………………….………………………..…....18 3.5 Instruments……………..…………………….……………………………….……...19 3.6 Analytical procedure…………………………………………………………………20 3.6.1 Sample preparation for monosodium glutamate analysis………………………….20 3.6.2 Sample derivatization for monosodium glutamate analysis……………………….20 vii 3.6.3 Sample preparation for aspartame analysis………………………………………...20 3.6.4 Sample preparation for sodium benzoate analysis…………………………………21 3.7 Standards preparation………………………………...…………….………...…..….21 3.8 Method validation……………………………………………………………....…....22 3.8.1 Linearity…………………………………………………………………………....23 3.8.2 Precision, accuracy and reproducibility……………………………………..……..23 3.8.3 Confirmation of additives and recoveries…………………………..………….…..23 3.8.4 Limit of detection………………………………………………………………..…24 3.9 Sample analysis………………………………………………………………………24 3.9.1 Analysis of monosodium glutamate…………………….………………………….24 3.9.2 Analysis of aspartame………………………………….…………………………..24 3.9.3 Analysis of benzoic acid………………………….………………………………..25 3.10 Quantification of the food additives………………………….…………………….25 3.11 Data analysis…………………………………………………...…………………...26 CHAPTER FOUR……………………….……………………………………………...27 RESULTS AND DISCUSSION……..………………………………………………....27 4.1 Method validation………………………………………………………………..…..27 4.1.1 Limits of detection……………………………………………………………..…..27 4.1.2 Linearity…...…………………………………………………………………...…..28 4.1.3 Precision, accuracy and reproducibility…………………………………..…..……28 4.1.4 Spiking of samples with standards……………...……………………….................30 4.2 The level of MSG in sauces………………………………………….……………....31 4.2.1 The MSG levels (g/kg) in various brands of chili sauces……………..…………...31 viii 4.2.2 The MSG levels (g/kg) in various batch numbers of chili sauces…………………33 4.2.3 The MSG levels (g/kg) in various brands of tomato sauces…………………....….34 4.2.4 The MSG levels (g/kg) in various batch numbers of tomato sauces………………36 4.2.5 Comparison of MSG levels in chili and tomato sauces from the four supermarkets……………………………………………………………………….38 4.3 Aspartame levels in sauces……………………………………………………….….39 4.3.1 Aspartame levels (mg/kg) in various brands of chili sauces…………………..…..39 4.3.2 Aspartame levels (mg/kg) in tomato sauces………………………………….……39 4.4 Benzoic acid levels in sauces…………………………………………………….…..40 4.4.1 Benzoic acid levels (mg/kg) in various brands of chili sauces…………………….40 4.4.2 The benzoic acid levels (mg/kg) in various batch numbers of chili sauces………..42 4.4.3 Benzoic acid levels (mg/kg) in various brands of tomato sauce…………………...43 4.4.4 The benzoic acid levels (mg/kg) in various batch numbers of tomato sauces……..46 4.4.5 Comparison of benzoic acid levels in chili and tomato sauces from the four supermarkets………………………………………………………………...…….47 CHAPTER FIVE……………………………………………………………………….52 CONCLUSIONS AND RECOMMENDATIONS……….………….………………...52 5.1 Conclusions…………………………………………………………………….….....52 5.2 Recommendations……………………………………………………………………52 5.2.1 Recommendations from this study……………………………………….…..….....52 5.2.2 Recommendation for further work…………………………………………………53 REFERENCES……………………………………………………………………...…..54 APPENDICES…………………………………………………………………………..59 Appendix I Map of Kenya showing Nairobi city centre………...………….……............59 ix Appendix II Different sauce brands sold in Nairobi supermarkets……..………..……....60 Appendix III Laboratory labeling and registration of sauces purchased from the supermarkets …….......................................................................................61 Appendix IV Batch numbers of the brands that were sampled from supermarkets A, B, C and D………………………...……………………………….…62 Appendix V Calibration curve for monosodium glutamate....…………..…………….…63 Appendix VI Calibration curve for aspartame……..…...…..…….……….……………..64 Appendix VII Calibration curve for benzoic acid………..………………………..……..65 Appendix VIII Chromatogram of monosodium glutamate standard…...….……..…..…66 Appendix IX Chromatogram of a sample analyzed for monosodium glutamate...…...…67 Appendix X Chromatogram of aspartame standard……...…………..…………………..68 Appendix XI Chromatogram of a sample analyzed for aspartame……...……………….69 Appendix XII Chromatogram of benzoic acid standard…………..……….……………70 Appendix XIII Chromatogram of a sample analyzed for benzoic acid…………..……...71 Appendix XIV The MSG levels (g/kg) in various chili sauce brands……...……………72 Appendix XV The MSG levels (g/kg) in various tomato sauce brands…..……………..73 Appendix XVI Comparison of MSG levels (g/kg) in chili and tomato sauces from the four supermarkets………………………………….………....74 Appendix XVII Benzoic acid levels (mg/kg) in various brands of chili sauce...………..75 Appendix XVIII Benzoic acid levels (mg/kg) in various brands of tomato sauce..……..76 Appendix XIX Comparison of benzoic acid levels in chili and tomato sauces from the four supermarkets……………...……………...……………....77 x LIST OF TABLES Table 2.1 Free and natural glutamate levels in variety of foods………...………………...9 Table 4.1 Detection limits of monosodium glutamate, aspartame and benzoic acid using HPLC……………………………………………………………………27 Table 4.2 Injection repeatability data and recoveries of three different amounts of reference standards………………………………………………..29 Table 4.3 Results of spiking the standard into the samples..…………………………….30 Table 4.4 The MSG levels (g/kg)