Exploratory Studies on the Carboxymethylation of Cassava Starch in Water-miscible Organic Media

The carboxymethylation of cassava starch using sodium monochloroacetate (SMCA) as an etherification agent was investigated. Mixtures of water and water-miscible organic liquids were selected as carboxymethylation reaction medium to obtain a high degree of substitution (DS) without changing the granular form and to prevent gelatinization. Factors that affect the process of chemical modification of cassava starch, including the type of solvents, the mass percentage of water in the reaction medium, the mass percentage of starch, the molar ratio of NaOH to SMCA, the theoretical DS (DSt), and the temperature were investigated experimentally. Isopropanol and tert-butanol appear to be the best solvents for the carboxymethylation process of cassava starch, and the optimum condition for this etherification reaction are a reaction medium consisting of about 10 wt% water, a reaction temperature between 50 and 55°C and a starch mass percentage between 4–8 wt%. When applying these conditions in combination with a DSt of 2.5, granular modified cassava starch with a DS of 1.4 can be obtained. The experimental results will be compared with those reported for other types of granular starches.