Gelatinization and thermal properties of modified cassava starches

The thermal properties of seven commercial modified cassava starches, including oxidized, acetylated, cross-linked, and combined acetylated and cross-linked starches were studied by differential scanning calorimetry (DSC) in the glassy and rubbery states. Increase in gel hardness in the rubbery state during storage was also monitored, as well as gelatinization behavior. The modified starches were prepared from granular starch and had a degree of substitution in the range 0-0.053. The glass transition temperatures (T-g) of the modified starches were 3-6 degrees C significantly lower than that of the non-modified starch. The physical aging peak temperatures were also significantly reduced by 2-3 degrees C, compared to the non-modified starch, while aging enthalpies increased. Starch modifications did not decrease amylopectin retrogradation significantly. During storage, the oxidized starch gel became significantly harder than the non-modified starch gel, while the hardness of the acetylated and/or cross-linked starch gels was significantly reduced, which confirmed that acetylation or cross-linking can decrease hardness, even when the extent of modification is limited. Different modifications controlled different properties of the starch system, with cross-linking and acetylation influencing the gelatinization behavior and the changes in starch gel texture during storage, respectively.