PRODUCTION OF COLD WATER SOLUBLE CASSAVA STARCH USING AQUEOUS SODIUM HYDROXIDE AND UREA SOLVENT SYSTEM
ABSTRACT
Starch obtained from cassava tubers was solubilized with aqueous NaOH/Urea (1:1) solvent system of varying concentration (2-8 wt%) at 250C . Reprecipitation of starch with ethanol resulted to products that were cold water soluble. The solubility of the product however, declined slightly from 92% that was obtained when the concentration of solvent system was 2% to 89% when 8% NaOH/Urea solution was used as solvent, The scanning electron micrograph of the modified starch revealed that dissolution and reprecipitation resulted in product of smaller particle size compared to the native starch.
CHAPTER ONE
1.0 INTRODUCTION
1.1 Starch is one of the most abundant materials produced by nature which has already been found in numerous industrial applications. It is a white tasteless substance that occurs in the form granules composed of two glucosidic macromolecular components. Amylose and Amylopectin. Amylopectin is a soluble polysaccharide (Amylose and Amylopectin, 2010) highly branched polymer of glucose found in plants. Amylose is a helical polymer made of L-D –glucose units, bound to each other. Nelson et al, (2008), starch is one of the cheapest biopolymer and could be totally biodegraded, this leading to the growing interest in non-food usage of starch. Starch has been the choice material for application in synthetic polymers. But the nature deficiencies of starch (such as insolubility in cold water, alcohol and other solvents, retrogradation at low temperatures e.t.c) limited its application.
Therefore, starch is usually modified to obtain a particular property, Great efforts has been made on production of starch derivatives to broaden the application range of this biopolymer. Further work for solvent that is suitable for solubulizing starch has been going. (Wim et al, 2006). However, the intact starch granules inhibit chemical reagents from making contact with the molecules in the crystalline region thus, chemical reactivity and reaction efficiency of native starch is usually low Le corre et al, (2012). There are many methods to modify the structure in crystalline structure, or decrease the size of crystalline regions to increase reaction activity of starch and convert native starch into gold water soluble starch. wim et al, (2006). Chemical methods like cross-linking, etherification, grafting and hydrolysis are applied in starch modification (Jane, 1992). Modification of starch is carried out to enhance positive attributes and get rid of short comings of native starch. They are developed to expand the usefulness of starch in industries.
Pregelatinized starch or cold water soluble starch is one of important physical modified starches used in pre-cooked or instant type foods. However, the pregelatinized starch upon dispersing in cold water shows more graininess, less sheen and less flexibility to processing conditions. Putchon, et al,(1981). Cold water solubility (CWS) is an important indicator for evaluating the physical properties of starch. It shows binding of water capacity of starch. Cold water solubility is related with the molecular structure of starch, particle size and content of amylase Singh and Singh (2003).
Cold water soluble starch was first produced by Eastman and Moore 1984, by slurry corn starch in selected aqueous alcohol under high temperature and pressure. Jane and stib, (1991) demonstrated an alcoholic alkali treatment for preparing cold water soluble starch which can be used on waxy and high amylase starches. This method was carried out by treating starch with mixture of alkali and ethanol, sodium hydroxide to swell starch granules. Treated starches are then neutralized with HCl, washed, and dried. Cold water soluble starch have been made subsequently from starches of diverse origin such as cold water soluble corn starch. Singh and Singh, (2003) potato starch, and banana starch was prepared using the same method (Arturo et al, 2000).
These processes that was used are costly and rigorous and often starches that are yielded possesses slight different morphology with viscosity that is usually lower than the corresponding native starch Singh and Singh, (2003) observed that alcoholic alkali treatment substantial changes in physio-chemical, morphological thermal and rheological properties of starches and so efforts have been made to find solvent system that can solubulize starch in a mild condition, With minimal degradation of polymer structure.
Recently, Xin et al (2012) employed NaOH (urea aqueous solution in solubulizing corn starch at low temperature below 25oc and consequently generated cold-water soluble starch from it, by precipitating with ethanol.
The aqueous NaOH/urea solvent system initially was utilized by Zhou and Zhang in 2000 for solubulization of cellulose. And so there is need to study its applicability to other starches of different source and examine the properties of different resulting solutions too.
In this work project because of the earlier mentioned problems of cost and rigorous process used in generating cold-water soluble starch using alcohol-alkali treatment and also the yield of starch that possesses a slight difference with viscosity that is lower than that of the corresponding native starch.
1.2 AIM AND OBJECTIVES
The study is aimed of producing cold-water soluble starch. However for the purpose of this study the objective is:
*To improve the cold-water solubility of cassava starch using NaOH/urea solvent system
*To determine some qualities of the resulting cold-water soluble starch from
cassava (I.e observing the granular structure of modified starch using an scanning electron microscope (SEM).
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