The aim of this study is to improve the Cold Water Solubility (CWS) and esterification activity of Native cassava Starch (NS) by pretreatment using NaOH (Sodium hydroxide) aqueous solution. The influence of pretreatment on granule shape and crystal structure of cassava starch was investigated by Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD). It has been found that the average particle size of Pretreatment cassava Starch (PS) decreased to nanometer level, smaller than those of NS (6-18 μm). XRD revealed that crystalline pattern of pretreated cassava starch was VH-type, which was different from that of Native cassava Starch (A-type). The maximum CWS of PS was 95.56%, while the NS was only 0.8%. NS and PS were esterified with oleic acid catalyzed by lipase under the same conditions respectively. The effects ofthe pretreatment on esterification activity of the cold water cassava starches were investigated by analyzing the Degrees of Substitutions (DS) of the esterification products. The maximum DS of pretreatment cassava starch oleate was 0.227, while the DS of native starch oleate was very low and even could not be detected.
Keywords: Cold water solubility, esterification activity, lipase, NaOH aqueous solution, pretreatment cassava starch.
TABLE OF CONTENTS
III. MODIFICATION OF STARCHES
IV. EFFECT OF MODIFICATION ON DIFFERENT PROPERTIES OF CASSAVA STARCH
V. MATERIALS AND METHOD
VI. RESULTS AND DISCUSSION
Starch is one of the most abundant materials produced by nature which has already been found numerous industrial applications. It is one of the cheapest biopolymer and could be totally biodegraded, this leading to the growing interest in the nonfood usage of starch. Starch has been the choice materials forapplication in synthetic polymers. But the nature deficiencies of starch (such as un-solubility in cold water, easy to aging, retrogradation at low temperatures and low film-forming ability) limited its application.
Therefore, starch is usually modified to obtain a particular property and to cater the requirements for its tailor-made. However, the intact starch granules inhibit chemical reagents from making contact with the molecules in the crystalline region, thus the chemical reactivity and reaction efficiency ofnative starch is usually low. There are many methods to modify the structure inthe crystalline region, or decrease the size of crystalline regions to increase reaction activity of starch and convert native starch into cold water-soluble starch. The Cold Water Solubility (CWS) is an important indicator for evaluation the physical properties of starch. It shows the water binding capacityof starch. The CWS is related with the molecular structure of starch, particle size and the content of amylase Cold-water soluble corn starch was first produced byEastman and Moore (Eastman, 1984), by slurring cassava starch in selected aqueous alcohols under the hightemperature and pressure. A method for preparinggranular cold water swelling/soluble starches byalcoholic-alkali treatments has been studied by Lim andJane (1992). Subsequently, some different origingranular cold-water-soluble starch such as cold-watersolublecassava starch (Singh and Singh, 2003), coldwatersoluble banana starch (Arturo et al., 2000), coldwater-soluble potato starch were prepared and studiedusing the alcoholic-alkaline method.
In this study, we reported an easy method to modify cassava starch through hydrolyzing by using Noah solution as hydrolytic agent and reprecipitatedout from the starch solution by addingethanol drop-wise. The aim of this study is to improvethe CWS of corn starch and to activate its reactionability of esterification. Also, the mechanism of themethod could improve the CWS and the esterificationreaction activity of corn starch was investigated. Tostudy the effect of process conditions on the CWS ofPS, a number of experiments were performed at various ratio of NaOH and the concentration of theaqueous solution of NaOH. Furthermore, theeffect of the pre-cooling temperature and the amount ofethanol on the CWS were explored. The esterificationreaction activity of PS with different CWS wascompared with NS.