Study on the effect of carboxymethylation on properties of rice starch

Using rice starch as a raw material,and chloroethanoic acid as ethrifying agent,the carboxymethyl rice starch of different substitution degree(DS=0.34~0.74) was prepared with isopropanol solvent method.The properties of the carboxymethyl starch,such as solubility,turgidity,transparency,freeze-thaw stability,retrogradation,gelatinization characteristic and particle structure,were investigated. The results of IR spectra showed that carboxymethyl carboxymethyl groups were introducted into rice starch molecules. The impact of carboxymethylation on the morphology of starch was analyzed by SEM. The results of scanning electron microscope indicated that carboxymethylation damaged the structure of starch granule and the extent of damage was related with DS. The results showed that retrogradation property of the carboxymethyl rice starch decreased due to the introducing of hydrophilic carboxymethyl groups. Compared with raw starch,the modified starch had better freeze-thaw stability,higher transparency,turgidity and solubility,and all these properties increased with the increase in carboxymethyl substitution degree. Besides, the gelatinization temperature significantly reduced and viscosity increased.