1.0 Introduction
1.1 Background of Study
Starch is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. This polysaccharide is produced by all green plants as an energy store. It is the most common carbohydrate in the human diet and is contained in large amounts in such staple foods as potatoes. Wheat maize (corn) rice and cassava (Michael et al, 2005). Pure starch is white tasteless and odorless power that is insoluble in cold water or alcohol. It consists of two types of molecules: the linear and helical amylase and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylase and 75 to 80% amylopectin. Glycogen, the glucose store of animals is a more branched Version of amylopectin (Mclver et al, 1999).
Starch is processed to produce many of the sugars in processed foods. Dissolving starch in warm water gives wheatpaste that can be used as a thickening; stiffening or gluing agent. The biggests industrial non-food use of starch is as adhesive in the papermaking process (Miller et al, 2008) Starch molecules among themselves in the plant in semi-crystalline granules. Each plant species has a unique starch granular size: rice starch is relatively small (about 2µm) while potato starches have large granules (up to 100um). Although in absolute mass only about one quarter of the starch granules in plants consist of amylase; there are about 150 times more amylase molecules than amylopectin molecules. Amylase is a much smaller molecule than amylopectin. (Willem et al, 2003).
Starch becomes soluble in water when heated the granules swell and burst; the semi-crystalline.
Structure is lost and the smaller amylase molecules start leaching out of the granule; forming a network that holds water and increasing the mixtures viscosity. This process is called starch gelatinization. During cooking the starch becomes a paste and increases further in viscosity. During cooling or prolonged storage of the paste; the semi-crystalline structure partially recovers and the starch paste thickness, expelling water. This is mainly caused by the retrogradation of the amylose. This process is responsible for the hardening of bread or stalling; and for the water layer on top of a starch gel (Synersesis) (Theisen et al, 2007).
1.2 Statement of Problem
Micro-organisms had made significant contribution to the production of foods and beverages in the last three decades.
This is mainly due to the extracellular enzymes produced by some of them. These extracellullar amylase produced have been found applicable in the bioconversion of starches and starch based substrates. These raw starch degrading enzymes are ubiquitous and produced by plants, animals and micro-organisms. Although microbial sources according to (Haiyan et al, 2009) is the most preferred one for large scale production.
1.3 Aim and Objective
The aim of this work is
- To isolate and screening of micro-organisms capable of degrading raw starch
- To assess the bacteria associated with starch
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