ABSTRACT
Irvingia gabonensis (IG) Baill and Celtis zenkeri (CZ) plant are used for various purposes such as timber and medicine. Physicochemical, spectroscopic and rheological studies of IG and CZ were carried out on the exudates. The analyses were carried out using standard procedures and the results were tested and compared with that of Acacia Senegal gum exudates. The results of the physiochemical analysis of Irvingia gabonensis and Celtis zenkeri gum exudates revealed that the gums are highly soluble in water with high amount of total dissolved solids. The exudates were odourless, tasteless and with pH values of 5.42 and 4.61 for Irvingia gabonensis and Celtis zenkeri gum exudates respectively. The viscosity values of the gum exudates were found to decrease with increase in temperature while increase in concentrations of the exudates was found to increase the viscosity of the gums. Addition of electrolytes such as KCl, KBr and AlCl3 was found to increase the viscosity of the gums. The concentration of metals presence in the study gums are manganese (213-146mg/kg), iron (375-311mg/kg), zinc (41-10mg/kg), lead (63-15mg/kg), magnesium (2285-2274mg/kg), cadmium (1.6-1.0mg/kg), calcium (2315-652mg/kg), copper (16.6-16.4mg/kg) and nickel (79-48mg/kg) for IG and CZ gums respectively. Surface morphology analyses indicate the shapes and dimension of the particles in addition to the amorphous nature of the gum particles. The measurement of fibre and pore shows that the pore areas for IG gum and CZ gums were 0.71μm2 and 0.02μm2 respectively while the fibre length ranged from 1.03 to 21.34μm and 53.35 to 1.52μm respectively. The Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the presence of C-C bending, CO2 bending, C-O stretch, C-H wag, C-H in plane bending, C=C stretch, C-D and C=O asymmetric stretch for both 1G and CZ gums. The data obtained from the different analyses give an insight into the possibility of using the plant gums as food additive, pharmacological and industrial applications.
TABLE OF CONTENTS
Cover page i Title page ii Declaration iii Certification iv Dedication v Acknowledgement vi Table of contents vii List of Tables xi List of Figures xii List of Plates xv Abbreviations xvi Abstract xvii CHAPTER ONE
1.0 INTRODUCTION 1
1.1 Justification for the Study 3 1.2 Aim of the Study 4 1.3 Objectives of the Study 4 CHAPTER TWO
2.0 LITERATURE REVIEW 5
2.1 Gums 5 2.1.1 Origin of gums 6 2.1.2 Classification of gums 6 2.1.3 Types of plant gum 7
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2.2 Gums Selected for the Study 9 2.2.1 Irvingia gabonensis 9 2.2.2 Celtis zenkeri 10 2.2.3 Acacia senegal (Reference gum) 11 2.3 Properties and Application of Plant Gum 11 2.4 Physicochemical Properties of Plant Gums 12 2.5 Measurement of Viscosity 17 2.5.1 Dilute solution viscosity 18 2.6 Studies on GC-MS, FTIR and SEM of Gums 18 2.7 Studies on Rheology of Gums 21 2.7.1 Effect of electrolytes on gums solution 24 2.8 Spectrophotometry and Spectroscopy 27 2.8.1 Absorption spectrophotometry 27 2.8.2 Ultra-violet (UV) spectroscopy 27 2.8.3 Atomic absorption spectroscopy 28 2.8.4 Scanning electron microscope 28 CHAPTER THREE
3.0 MATERIALS AND METHODS 30
3.1 Materials 30 3.2 Tapping of Gums 30 3.3 Purification of the Gum 31 3.4 Physicochemical Analysis 31 3.4.1 Determination of pH and conductivity 31 3.4.2 Determination of solubility in various solvents 31 3.4.3 Density 32
3.4.4 Determination of the viscosity of the gum mucilage 32
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3.5 Effect of Temperature, Concentration and Electrolytes on Viscosities of Gums 33 3.6 Heavy Metals 34 3.7 SEM Analysis 34 3.8 FTIR Analysis 35 3.9 GC-MS Analysis 35 CHAPTER FOUR
4.0 RESULTS 37
4.1 Physicochemical Properties 37 4.2 Effects of Temperature, Concentration and Addition of Electrolytes on the Viscosity of the Gum Solutions 37 4.3 Metals Concentration 37 4.4 Surface Morphology 37 4.5 SEM Elemental Analysis 56 4.6 Fibre and Pore Measurement 56 4.7 FTIR 56 4.8 GC-MS 56 CHAPTER FIVE
5.0 DISCUSSION OF RESULTS 100
5.1 Physicochemical Properties 100 5.2 Effects of Increase in Temperature and Concentration of the Gum on Viscosity Value 101 5.3 Effects of Electrolytes on the Viscosity of the Gums 102 5.4 Metals Composition 103 5.5 Surface Morphology 105 5.6 SEM Elemental Analysis 106 5.7 Fibre and Pore Measurement 107
5.8 FTIR 108
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5.9 GC-MS 109 CHAPTER SIX
6.0 CONCLUSION AND RECOMMENDATION 111
6.1 Conclusion 111 6.2 Recommendation 112 REFERENCES References 113 APPENDICE Appendix 1 124 Appendix 2
CHAPTER ONE
1.0 INTRODUCTION A gum in general, is any water-soluble or water-swellable polysaccharide that is extractable from marine and land plants, or from microorganisms that possess the ability to contribute viscosity or gelling ability to their dispersions (Abu Baker et al., 2007). The most fundamental property of a gum therefore is its water solubility and high viscosity in aqueous dispersions. Among the advantages of natural gums over their synthetic counterparts are their biocompatibility, low cost, low toxicity (eco-friendliness) and relative widespread availability (Odeku, 2005; Emeje et al., 2009; Nep and Conway, 2010; Ogaji and Okafor, 2011). Plant gums are organic substances obtained as an exudation from fruits, trunk or branches of the trees spontaneously or after mechanical injury of the plant by incision of the bark or after the removal of the branch or after invasion by bacteria or fungi (Ahmed et al., 2009). They are capable of displaying colloidal properties in an appropriate solvent or swelling agent. According to Ahmad et al. (1994), most plant gums are polyelectrolytes, which is a class of polymers that bears a large number of ionizable groups on the main chain. Gums have numerous applications in several industries. For example, Albizia zygia and some Albizia lebbeck gums have been found to be useful as natural emulsifiers for food and pharmaceuticals (Mhinzi, 2002). According to DePaula et al. (2001) Albizia lebbeck gum exudate is also used as a substitute for Arabic gum in the metallurgical industries. Guar and some other gums have a number of applications in the mining and mineral processing industry (Ma and Pawlik, 2007). In the froth flotation of base metal and platinum group metal ores, guar gum is used as a depressant of naturally hydrophobic waste minerals such as talc. The role of the polysaccharide is to adsorb on the talc surface, render it hydrophilic and prevent its flotation (Ma and Pawlik 2007).
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The principal use of plant gums is in foodstuffs because of their ability to impart desired qualities to foods by influencing their viscosity, body and texture; most frequently in confectionery food, flavouring and soft drinks. They also have pharmaceutical and industrial applications as demulcents, adhesives in pill manufacture, lithography, paints, inks, corrosion inhibitors and as emulsifying agents. The use of natural gums exudates and extracts of plants, have been given a strong consideration due to its high value for industrialization and to the international market, example being Gum Arabic which in current production potential, is around 30,000 to 40,000 tonnes per annum, Virtually all gum arabic in the Sahelian zone is exported, either immediately or after a period of storage or stockpiling. Sudan dominates the world exports, accounting for 70% to 80%, the balance being accounted for by the Sahelian countries of West Africa (Nigeria, Mali, Niger, Burkina Faso, Chad, Tanzania and Kenya). One billion pounds are consumed in the United States each year where the growth in demand exceeds 8% per year (Yusuf et al., 2006). Another example is the cashew gum, which by natural exudation or by means of incisions, produces a gum or resin of a yellowish colour, soluble in water, and which presents a great potential for industrialization, appears on the trunk and branches of the cashew tree. It is similar to gum arabic and may be used as a substitute for liquid glue for paper. In the pharmaceutical and cosmetic industry it is used as an agglutinant for capsules and pills while in the food industry as a stabilizer of juices, beer and ice cream, as well as for clarification of juices, and can also be utilized in the making of cashew wine. Besides proving to be strong wood glue when mixed with water, it presents a fungicidal and insecticidal action and because of this it is much used in book binding. Research already exists on its utilization in the making of inks and varnishes (Emeje et al., 2009)
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These gums find wider application because of their physical, rheological and chemical properties such as properties include solubility, water sorption, swelling capacity, pH, effect of temperature, and viscosity among others (De Paula et al., 2001). Ficus glumosa is an example of lesser known plant producing gum the plant commonly called African rock fig tree in English and „Kawuri‟ in Hausa belongs to the family, Moraceae. Ficus glumosa, a tall plant of about 24 meters in height and about 3 meter in diameter, occurs on rocky outcrops, where it splits rocks; along dry water course or in open boundry; frequently in valleys, where it reaches its greatest size (Keay, 1989) The species also occurs in fringe forest in savannah areas, especially in swampy ground, and in swamp forest in coastal areas (Arbonnier, 2004). The bark also contains abundant sticky white latex which is used in Northern Nigeria like bird-lime to trap crickets (Ameh, et al., 2012). The exudate is also chewed (chewing-gum) and used for fastening arrowheads to their shaft. 1.1 Justification of the Study There is increasing demand for gums globally because of their vast applications leading to increase in prices of the existing ones in the local and international markets. For the price to be stable and less expensive there is need to look for alternative suitable natural gums which will have similar characteristics to the existing ones. In view of the numerous applications that have been discovered for plant gums and the dependence of the applications on physicochemical, rheological, surface morphology and other properties of the gums, there is the need to assess these properties for gums that have not been adequately studied and thereby providing a means of references for future use.
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1.2 Aim of the Study The aim of the study is to determine the physical and chemical properties of the plant gums from Irvingia gabonensis and Celtis zenkeri, and compare the properties of the plant gums with Gum Arabic (Acacia senegal) which is one of the most commercially used plant gum. 1.3 Objectives of the Study The above aim will be achieved through the following objectives:
i. Tapping and purification of the gum exudates from the parent plant species;
ii. Investigating the functional groups present using fourier transform infrared spectroscopy (FTIR);
iii. Analyzing the chromopores present within the chemical components using ultra violet spectroscopy (UV);
iv. Identifying the metals present using atomic absorption spectrometry;
v. Determining the rate of flow of the gums by the use of a cannon ubbelohde cappilary viscometer;
vi. Determining the effects of temperature, concentration and addition of electrolytes on the viscosity of the gums;
vii. Determining the fibre and pores measurement using scanning electron microscope;
viii. Analyzing the surface morphology by the use of scanning electron microscope;
ix. Determining the elements present using scanning electron microscope.
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