Abstract
The role of reaction variables on carboxymethylation of cassava starch was investigated using a statistically experimental design approach. The reaction; was carried out in an isopropanol-water mixture at 40degreesC for 3 h. The reaction parameters under investigation included water fraction in the reaction medium, the ratio of sodium hydroxide to anhydroglucose unit (AGU) and the ratio of sodium, monochloroacetate (SMCA) to AGU. The dependent responses were degree of substitution (DS) of CMS and the reaction efficiency (RE) of the carboxymethylation. Carboxymethyl cassava starches with DS in the range of 0.01 to 0.86 were prepared. The result from regression analysis indicated that the most important factors in controlling the DS of CMS were sodium hydroxide and SMCA contents followed by water content. Response surface plots suggested! that the optimal levels of sodium hydroxide and water content to achieve CMS with high DS were at the intermediate values. Similar effects of sodium hydroxide and water content were also observed on the RE while SMCA content had a negative effect; increasing SMCA content resulted: in lower RE, The optimal, conditions to achieve the highest DS and RE were found to be at a water content of 17-19% with a molar ratio of sodium hydroxide to AGU of 1.8-1.9, and a molar ratio of SMCA to AGU between 1.1-1.5. Carboxymethyl cassava starch with various DS was also prepared. The properties of CMS as affected by the degree of modification were also discussed.
