NUTRITIONAL COMPOSITION AND IN VITRO STARCH DIGESTIBILITY OF CRACKERS FROM PEARL MILLET AND WHEAT COMPOSITED WITH MUSHROOMS A THESIS SUBMITTED IN FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE IN AGRICULTURE (FOOD SCIENCE AND TECHNOLOGY) OF THE UNIVERSITY OF NAMIBIA BY ERICK N. UUKULE 201146924 MARCH 2020 SUPERVISOR: DR. KOMEINE NANTANGA (UNIVERSITY OF NAMIBIA) ABSTRACT Type 2 diabetes is a global problem that can be controlled by a diet that consists of carbohydrates with substantial amounts of slowly digestible starch amongst others. Pearl millet (Pennisetum glaucum (L) R. Br.) is an underutilised cereal crop that in recent times, raised interest due to its health benefits. The low starch hydrolysis rate of pearl millet is particularly of interest in type 2 diabetes modulation. To contribute to the value-addition and food diversification using pearl millet, this project investigated the nutritional content and starch digestibility of composite flours and crackers made of pearl millet-wheat, truffle (Kalaharituber pfeilii) and Oyster mushroom (Pleurotus ostreatus) composite flours and crackers. Equal amounts of fermented whole pearl millet grain and bread wheat flour were mixed. Of this mixture, 5%, 10% and 15% were substituted with Oyster mushroom and Kalahari truffle powders. The moisture, fat, protein, ash and minerals contents, water absorption (WAI) and water solubility (WSI) indices, total starch and starch digestibility of the flour formulations and the resultant crackers were determined. The consumer acceptance of the composite crackers was also assessed. The ash content, WSI and WAI were higher in the mushroom flours than in the cereals composite flours. Contrary, mushroom containing flours had the lowest starch content of all the flours. For crackers, ash content, WAI and WSI were directly proportional to the levels of mushroom incorporation. In terms of consumer acceptance, 5% oyster mushroom and 5% Kalahari truffle incorporated crackers scored the highest on the 9 point hedonic scale. Starch digestibility of mushroom incorporated flours and crackers were lower than those of cereal composite products. The higher the mushroom incorporation level, the slower the glucose release rate, showing that mushroom incorporation may be beneficial to people with type 2 diabetes. i LIST OF PUBLICATIONS OF CONFERENCE PROCEEDINGS Uukule, E.N., Embashu, W., Nantanga, K.K.M. and Kadhila-Muandingi N.P. Towards improved control of Type 2 diabetes: use of pearl millet and Kalahari truffle. PowerPoint presentation at the second annual International Conference on Agriculture and Natural Resources (ICANR), 15-16 October 2018, Neudamm Campus, University of Namibia. ii TABLE OF CONTENTS ABSTRACT ............................................................................................................. i LIST OF PUBLICATIONS OF CONFERENCE PROCEEDINGS .......................... ii LIST OF TABLES ................................................................................................. vii LIST OF FIGURES .............................................................................................. viii LIST OF ABBREVIATIONS AND ACRONYMS ................................................. ix ACKNOWLEDGMENTS ........................................................................................ x DEDICATION....................................................................................................... xii DECLARATIONS ................................................................................................ xiii CHAPTER 1 ............................................................................................................ 1 INTRODUCTION ................................................................................................... 1 1.1 BACKGROUND OF THE STUDY ................................................................... 1 1.2 Statement of the problem ................................................................................... 2 1.3 Research questions ............................................................................................. 4 1.4 Hypotheses......................................................................................................... 4 1.5 Significance of the study .................................................................................... 5 CHAPTER 2 ............................................................................................................ 6 LITERATURE REVIEW ......................................................................................... 6 2.1 Pearl millet ......................................................................................................... 6 2.1.1 Production and distribution .......................................................................... 6 2.1.2 Grain structure ............................................................................................. 7 2.1.3 Nutrient composition ................................................................................... 9 2.1.4 Processing and uses of pearl millet..............................................................10 2.1.4.1 Milling .................................................................................................10 2.1.4.3 Grain fermentation ...............................................................................11 2.1.5 Effect of pearl millet on health ................................................................13 2.2 Edible mushrooms.............................................................................................15 2.2.1 Oyster mushrooms (Pleurotus ostreatus) and Kalahari truffle (Kalaharituber pfeilli) .....................................................................................................................16 2.2.2 Oyster mushrooms .........................................................................................16 2.2.2.1 Production and Distribution .....................................................................16 2.2.2.2 Structure ..................................................................................................17 2.2.2.3 Composition ............................................................................................19 iii 2.2.2.4 Processing and uses .................................................................................20 2.2.2.5 Health benefits of oyster mushroom consumption ....................................23 2.2.2.5.1 Anti-diabetic properties .....................................................................23 2.2.2.5.2 Antimicrobial and anti-oxidant properties ..........................................24 2.2.3 Desert Truffles (Kalaharituber pfeilii) ............................................................24 2.2.3.1 Growth and distribution ...........................................................................25 2.2.3.2 Structure ..................................................................................................26 2.2.3.3 Composition ............................................................................................27 2.2.3.4 Uses .........................................................................................................27 2.2.3.5 Health benefits of truffles consumption ....................................................28 2.3 Crackers Manufacturing ................................................................................29 2.3.1 Why crackers?.........................................................................................30 2.3.2 Crackers and nutrition .............................................................................31 2.4 Starch digestibility ............................................................................................32 2.5 Sensory evaluation ............................................................................................33 CHAPTER 3 ...........................................................................................................35 RESEARCH ...........................................................................................................35 Pearl millet-wheat, Kalahari truffle and Oyster mushroom composite flours: Some functional and nutritional aspects ............................................................................36 Abstract ...............................................................................................................36 3.1 Introduction ...................................................................................................37 3.1.2 Materials and methods ................................................................................38 3.1.2.1 Pearl millet and wheat flours ................................................................38 3.1.2.2 Mushrooms ..........................................................................................39 3.1.2.3 Composite flours formulation ...............................................................40 3.1.2.4 Proximate composition of composite flours ..........................................40 3.1.2 .5 Water absorption and Solubility indices...............................................40 3.1.2.6 In vitro starch digestibility ....................................................................41 3.1.2.7 Statistical analysis ................................................................................41 3.1.3 Results and Discussion ...............................................................................41