Presently, rice cultivars are categorized according to amylose content into three groups: low, medium and high amylose content cultivars. The correlation of amylose content with gelatinization properties, retrogradation, and pasting properties of eleven cultivars of Thai rice were investigated. Rice flour was prepared from milled rice by the wet grinding process. Onset (To), peak (Tp) and conclusion (Tc) temperatures of gelatinization, (determined by DSC) were found to be highly positively correlated with amylose levels. This correlation could be used for prediction of amylose content of rice flour. Low amylose starch could also be characterized by low degree of retrogradation (%R). The data obtained from RVA‐viscograms (peak viscosity, breakdown, setback, and pasting temperature) can be used only for characterization of the group of low amylose starches (waxy rice). It was demonstrated that low amylose rice starch provided the highest peak viscosity and breakdown and the lowest setback and pasting temperature among the groups investigated.

Tapioca starch was partially hydrolyzed in hydrochloric acid solution at room temperature for various lengths of time to obtain high‐crystalline starches. RVA viscoamylograms of acid‐modified starches demonstrated a very low viscosity as compared to that of native tapioca starch. The relative crystallinity of native and acid‐modified tapioca starches were measured by X‐ray diffraction ranging from 39.53% to 57.75%. The native and acid‐modified tapioca starches were compressed into tablets using various compression forces. The % relative crystallinity of starch increased with the increase in hydrolysis time and the crushing strength of the tablet was also increased in line with the crystallinity while the amylose content decreased when the crystallinity increased. These results suggested that the erosion of amylose might cause the rearrangement of starch structure into a new more tightly packed form, which provided the higher crushing strength for the tablets.

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The efficiency of sago and tapioca starch stearates for encapsulating lemon oil were studied and compared to the efficiency of gum arabic. The stearates were prepared by esterification of stearic acid with starch. To accomplish esterification, the stearic acid was first coated on the surface of the starch granules. Then the coated granules were heated at 150°C for 2 h to obtain sago or tapioca starch stearate (SSS or TSS). SSS or TSS can be prepared as ready-to-use products in the form of pregelatinized-hydrolyzed sago or tapioca starch stearate (PGHSSS or PGHTSS). The resulting modified starches were used for encapsulation of lemon oil. The lemon oil encapsulating efficiency for SSS with DS 0.009 and 0.014 were close to that of gum arabic, whereas the encapsulating efficiency for PGHSSS with DS 0.0052 and 0.016 were higher than that of the gum arabic. The TSS and PGHTSS provided encapsulating efficiencies lower than the gum arabic.

Tapioca starch was oxidized by periodic acid (sodium metaperiodate plus hydrochloric acid) to form dialdehyde tapioca starch (DAS). The influence of periodate concentration (NaIO4, 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 (To and Tp) 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°C and 70°C, but was lower at 80°C and 90°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.