ENHANCEMENT OF THE NUTRITIVE VALUE OF COCOA (THEOBROMA CACAO) BEAN SHELLS FOR USE AS FEED FOR ANIMALS THROUGH A TWO- STAGE SOLID STATE FERMENTATION WITH PLEUROTUS OSTREATUS AND ASPERGILLUS NIGER

Thesis Overview

<p> <b>1.0 INTRODUCTION</b></p><p><b>1.1 BACKGROUN D STUDY&nbsp;</b></p><p>&nbsp;Cocoa (Theobroma cacao) tree is widely cultivated in Ghana. In addition to the highly flavoured cocoa products, cocoa tree provides by-products such as Cocoa Bean Meal (CBM), Cocoa Pod Husk (CPH) and Cocoa Bean Shell (CBS), among others. Cocoa bean shell (CBS) is an industrial ligno-cellulosic waste material produced at cocoa and chocolate factories, especially in the industrialized countries and it forms 12-14% of the roasted cocoa bean (Aina, 1998). CBS is a potential tropical feed resource and its utilization in animal feeding will greatly reduce the disposal problem facing the cocoa processing factories (Aina, 1998). The dried CBS contains 13.12% crude protein; 13.00% crude fibre; 8.71% ether extract; 9.15% ash (Olupona et al., 2003). Several studies on broilers, cockerel chick finishers and laying hens have established the inclusion rate of CBS in these poultry rations though they reported a low growth performance at higher inclusions due to several factors (Olubamiwa et al., 2000; Hamzat and Babatunde, 2006) Gohl (1981) attributed the limited use of CBS in animal feeds to its theobromine content in spite of its high nutritive value. Theobromine belongs to the same naturally occurring methylated xanthine group as caffeine (Ching and Wong, 1986). When taken in modest quantities, it acts as a stimulant like caffeine but intake of more than 0.0279kg per body weight is injurious to animals (Menon, 1982). Menon (1982) indicated that the anti-nutritional compound could be reduced by heat, sun-drying and boiling. Poor monogastric utilization of CBS- based diets is partly attributed to the high fibre content of CBS (Hamzat et al., 2006) Most of these by-products, which are often referred to as agro-industrial by-products (AIBPs) contain certain complex carbohydrates termed lignocellulose which are very difficult to degrade naturally into simpler forms (Howard et al., 2003). Lignocellulose is the major structural component of woody plants and non-woody plants such as grass and represents a major source of renewable organic matter. Lignocellulose consists of lignin, hemicellulose and cellulose (Howard et al., 2003). The chemical properties of the components of lignocellulosics make them a substrate of enormous biotechnological value (Malherbe and Cloete, 2003). Large amounts of lignocellulosic materials are generated through forestry and agricultural practices, paper-pulp industries, timber industries and many agro industries and they pose an environmental pollution problem. Majority of these lignocellulose wastes are often disposed of by biomass burning, which is not restricted to developing countries alone, but is considered a global phenomenon (Levine, 1996). However, the huge amounts of residual plant biomass considered as “waste” can potentially be converted into various different value-added products including biofuels, chemicals, and cheap energy sources for fermentation, improved animal feeds and human nutrients. Lignocellulytic enzymes also have significant potential applications in various industries including chemicals, fuel, food, brewery and wine, animal feed, textile and laundry, pulp and paper and agriculture. With the advent of fungal biotechnology, highly fibrous agro-wastes can be made useful to animals particularly monogastrics by fermentation with certain fungi such as Pleurotus spp. capable of improving protein quality and fibre digestibility (Alemawor et al., 2009). The fermentation process also enhances micronutrient bioavailability and aids in degrading antinutritional factors (Achinewhu et al. 1998). The use of fungi for the conversion of lignocelluloses into food or feed rich in protein offers an alternative for developing nonconventional sources of proteins as food or feed (Vijay et al., 2007). Mushroom is defined by Chang (1980) as a fungus with a distinctive fruiting body which can be either epigeous or hypogenous and has visible growth on lignocellulosic materials used as substrates. Mushroom forming fungi are therefore amongst nature’s most powerful decomposers, secreting strong extracellular enzymes due to their aggressive growth and biomass production (Adenipekun, 2009). They are primary decomposers and saprophytic fungi, which grow easily in clusters on decomposing lignocellulosics, capable of utilizing a wide range of substrate materials with high biological efficiency and good mycelia growth rate (Achio, 2009). They undergo extracellular digestion hence their capability of producing a wide range of enzymes such as laccases, cellulases and hemicellulases that are responsible for the breakdown of complex polysaccharides such as lignin, cellulose and hemicellulose respectively into simpler soluble substances which are highly absorbable for growth and development (Sharma et al., 1999). Mushrooms therefore grow very well on lignocellulosic substrates containing mainly cellulose and lignin converting them into digestible materials which may be used as animal feed (Sharma et al., 1999). Some of the lignocellulosic materials are sawdust, rice bran, rice straw, corncobs, cocoa by-products, sugarcane leaves, grasses, rice hull, cassava peels, etc. These agricultural wastes can be used for the cultivation of mushroom which provides not only food and feed at low cost but also help reduce the incidence of environmental pollution (Sharma et al., 1999). Pleurotus ostreatus is a white- rot fungus which forms a sheet of white-like spores on the surface of substrates on which they colonize. A wide range of lignocellulosic substrates are used for cultivation of Pleurotus species. Amongst the cereal straws, Garcha et al., (1984) reported paddy straw to be the best substrate for the cultivation of oyster mushroom and further reported the use of pearl millet stalks in the cultivation of P. sajor-caju. Rice straw waste, lawn grass, maize cobs, banana wastes (Bonatti et al., 2004) and maize straw (Bahukhandi and Munjal, 1989) were reported as suitable substrates for cultivation of different Pleurotus spp. A study conducted by Alemawor et al., (2009) on fermentation of cocoa pod husk, a cocoa byproduct with Pleurotus ostreatus reported that the alkaloids in the cocoa pod husk was not affected by the P. ostreatus fermentation unlike the polyphenols such as tannins which was significantly reduced. However, Aspergillus niger has proven to be capable of biodegrading alkaloids such as theobromine when used in the fermentation of cocoa by-products by using the theobromine as its sole carbon and energy sources (Adamafio et al., 2011). Aspergillus niger is a fungus and one of the most common species of the genus Aspergillus. It is known for its black sporulation and ubiquitous nature hence a major contaminant in laboratory cultures. A. niger is often cultured for the industrial production of many substances. Various strains of A. niger are used in the industrial preparation of citric acid (E330) and gluconic acid (E574) (Papagianni et al., 1994) and have been assessed as acceptable for daily intake by the World Health Organization. A. niger fermentation is "generally recognized as safe" (GRAS) by the United States Food and Drug Administration (US FDA) (Schuster et al., 2002) <br></p>