University of Ghana http://ugspace.ug.edu.gh COLLEGE OF BASIC AND APPLIED SCIENCES SCHOOL OF BIOLOGICAL SCIENCES MICROBIAL INACTIVATION BY GAMMA IRRADIATION OF POWDERED SUN-DRIED LEGON-18 PEPPER (CAPSICUM ANNUUM L.) AND ITS IMPACT ON PRODUCT QUALITY BY BERNARD TAWIAH ODAI THIS THESIS IS SUBMITTED TO THE UNIVERSITY OF GHANA, LEGON, IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF DOCTOR OF PHILOSOPHY DEGREE IN FOOD SCIENCE DEPARTMENT OF NUTRITION AND FOOD SCIENCE July, 2019 University of Ghana http://ugspace.ug.edu.gh DECLARATION i University of Ghana http://ugspace.ug.edu.gh DEDICATION This thesis is dedicated to the Glory of God and to the memory of my late daddy, Julius Nii-Odai who was a source of motivation to me in my academic endeavour. ii University of Ghana http://ugspace.ug.edu.gh ACKNOWLEDGMENTS My sincerest and profound gratitude to the Almighty God for bringing me this far in my career. I am grateful to all my supervisors for their support throughout this study. Grateful for their inputs. Thanks to the Ghana Atomic Energy Commission especially, Prof. B. J. B. Nyarko, Prof. K. E. Danso and Mr. A. Adu-Gyamfi for the permission granted me to pursue the programme. I am highly indebted to Mr. M. L. Akye and Mr. C. Bonsu of Noguchi Memorial Institute for Medical Research (NMIMR) for the various assistance offered during the period of working in the Bacteriology Department of the Institute. I am grateful for the assistance offered to me by the staff of the Central Laboratory at KNUST, Dr. D. Azanu, Mr. W. Appaw and colleagues, and Mr. Solomon Dowuona of Food Research Institute. Finally, I so much appreciate the supportive role played by family, especially my mother and siblings. iii University of Ghana http://ugspace.ug.edu.gh ABSTRACT Pepper powder (being a spice) has been known to be contaminated with several pathogenic microorganisms. These organisms tend to make red pepper powder a source of potential health hazard. The FAO/WHO preliminary report indicated a global concern on the management of these pathogens in foods and the need to reduce or eliminate the health hazards associated with them. Some of these pathogens have been identified with both dried and powdered pepper samples in Ghana. This warranted a study to investigate the use of gamma irradiation on these pathogens in Legon-18 (Capsicum annuum L.) pepper powder and also to determine the impact of the gamma radiation treatment on the quality parameters of the samples stored at two different temperatures. Samples of powdered Legon-18 pepper were obtained from a local farmer. Known weights of the samples were sterilised by gamma irradiation at 20 kGy, and a cocktail of Listeria monocytogenes, Bacillus cereus, Salmonella Typhimurium, Staphylococcus aureus and Escherichia coli of pre-determined cell count (colony forming unit/millilitre), were inoculated into them. The samples were irradiated at 1, 2, 4, and 5 kGy with 0 kGy as control, to determine an effective dose of gamma irradiation that could lead to complete inactivation of the pathogens inoculated in the samples. The samples were stored at 4 oC and 28±2 oC. Enumeration of the different pathogens was carried out on days 0, 2, 5, 12, 21, 30, 45 and 60 in storage. The effects of gamma irradiation and storage on the quality parameters of unsterile samples were determined. These were irradiated at 1, 2, 4 and 5 kGy. Unirradiated samples served as control (0 kGy). The CIELAB colour components were determined using the Minolta Chroma-meter. Carotenoids and capsaicinoids in the samples were quantified using high performance liquid chromatography. The results suggest that gamma irradiation treatment completely inactivated L. monocytogenes and S. Typhimurium only at day 60 at 2 and 4 kGy. E. coli could not thrive in the samples after 30 days of storage when not exposed to gamma irradiation. S. aureus could be completely inactivated at 4 kGy only after 45 days (no detection of S. aureus in the samples after). All iv University of Ghana http://ugspace.ug.edu.gh the pathogens could be completely inactivated at 2, 4 and 5 kGy. The optimum dose for complete inactivation of the pathogens excluding B. cereus was 2 kGy which is subject to a storage period of over 45 days. All pathogens used in the study were completely inactivated at 5 kGy even on day zero. Gamma irradiation treatments and storage significantly (p<0.05) affected the quality parameters of the samples. Losses of colour parameters, carotenoids and capsaicinoids were more pronounced in the samples that were stored at 28±2 oC as compared with the samples that were stored at 4 oC. Percentage losses for the samples stored at 4 oC were in the range of 83.32 and 83.81%, 50.00% to 53.72%, 33.53% to 37.80%, 54.52% to 58.60%, 40.25% and 56.00%, 78.35 to 81.71% and percentage increase in the range of 372.36% to 429.14% for lightness, redness, yellowness, browning index, chroma, hue and total colour difference respectively. The total colour difference, hue, chroma, browning index, yellowness, redness and lightness of the samples that were stored at 28±2 oC were in the range of 410.72% to 417.50%, 80.13% to 84.75%, 39.55% to 57.00 %, 50.69% to 54.02%, 32.98% to 37.37%, 51.86 to 55.06, 72.77 to 76.98% respectively. Moisture content, total titratable acidity and pH of the samples were stable. Capsaicinoid content ranged from 118 in the unirradiated samples to 221.00 (mg/100g) in the irradiated samples. At the end of the storage period there was a loss of 22.46%, 9.95%, 11.78%, 9.86% and 9.53% in the samples that were irradiated at 0, 1, 2, 4and 5 kGy respectively and stored at 4 oC and for the unirradiated samples, 16.43%, 11.11%, 10.31% and 10.67% for the samples that were irradiated at 1, 2, 4 and 5 kGy respectively and stored at 28±2 oC. Gamma irradiation caused an increase of 6.33, 17.68, 18.79 % and 20.95% in the samples irradiated at 1, 2, 4 and 5 kGy respectively. Beta cryptoxanthin, beta carotene and capsanthin ranged from 1.04 to 2.11, 5.36 to 10.27 and 1.12 to 1.48 (mg/100 g) in the irradiated samples, respectively. Gamma irradiation and storage caused some reductions in the contents of all the pigments analysed (p<0.05). v University of Ghana http://ugspace.ug.edu.gh TABLE OF CONTENTS DECLARATION ................................................................................................................. i DEDICATION .................................................................................................................... ii ACKNOWLEDGMENTS ................................................................................................. iii ABSTRACT ...................................................................................................................... iv TABLE OF CONTENTS .................................................................................................. vi LIST OF TABLES ............................................................................................................. xi LIST OF FIGURES ......................................................................................................... xiii LIST OF ABREVIATIONS ............................................................................................. xv CHAPTER ONE ................................................................................................................. 1 1.0 GENERAL INTRODUCTION .................................................................................... 1 1.1 Background ............................................................................................................... 1 1.2 Rationale ................................................................................................................... 2 1.3 Objectives .................................................................................................................. 3 1.3.1 Main Objective ................................................................................................ 3 1.3.2 Specific objectives .......................................................................................... 4 CHAPTER TWO ................................................................................................................ 5 2. 0 LITERATURE REVIEW ............................................................................................ 5 2.1 Spices ........................................................................................................................ 5 2.2 Peppers: origin, botany and production .................................................................... 6 2.3 Nutritional Composition ........................................................................................... 7 2.4 World production and economic importance .......................................................... 10 2.5 Characteristics and quality indices of chili pepper and pepper products ................ 11 2.5.1 Colour ............................................................................................................ 11 2.5.2 Pungency ....................................................................................................... 12 2.6 Uses of chili pepper and pepper products ............................................................... 14 2.7 Pepper production in Ghana .................................................................................... 14 2.8 Microbial ecology of chili pepper powder .............................................................. 15 2.9 Processing ..............................................................................................................