PRODUCTION OF COLD WATER SOLUBLE CASSAVA STARCH USING AQUEOUS SODIUM HYDROXIDE AND UREA SOLVENT SYSTEM

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 25^oc 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).