Preparation and physicochemical properties of dialdehyde tapioca starch

Tapioca starch was oxidized by periodic acid (sodium metaperiodate plus hydrochloric acid) to form dialdehyde tapioca starch (DAS). The influence of periodate concentration (NalO(4), 0.05 N, 0.1 N, 0.2 N and 0.3 N) on the physicochemical properties of DAS such as aldehyde and carboxyl contents, relative crystallinity, thermal properties, pasting properties, swelling power, solubility and molecular weight distribution was investigated. The results indicated that aldehyde and carboxyl contents of DAS increased linearly with the increasing of periodate concentration. X-ray diffraction patterns of DAS remained unchanged after periodate oxidation whereas the relative crystallinity decreased as periodate concentration increased. Furthermore, the gelatinization temperatures (T-o and T-p) of DAS were also increased, whereas the gelatinization enthalpy decreased. As determined in the Rapid Visco Analyser, the periodate oxidation increased the pasting temperature and peak viscosity as well as breakdown of the tapioca starch. The swelling power of DAS was higher than that of unmodified tapioca starch at 60 degrees C and 70 degrees C, but was lower at 80 degrees C and 90 degrees C. However, the solubility was higher than that of native tapioca starch at all incubation temperatures. Both amylose and amylopectin fractions were degraded during the oxidation reaction as measured by HPSEC. The thermal stability of DAS at boiling temperature was also investigated and depolymerization of the DAS could not be detected at any heating time as demonstrated for the thermal stability of the DAS.