Characterization of low-substituted hydroxypropylated canna starch

Starch isolated from rhizomes of edible canna (Canna edulis) was hydroxypropylated with propylene oxide at 40 °C and pH 5.5, and its physicochemical, morphological, thermal and gel textural properties were investigated. The extent of hydroxypropylation measured as molar substitution (MS) was 0.01, 0.02, 0.03, 0.07 and 0.11 when propylene oxide at 0.5, 1.0, 2.0, 5.0 and 10.0% (v/w), respectively, was used. Granular size and shape, as well as X-ray diffraction pattern of the modified starches, were similar to those of the native starch. Investigation on pasting properties of 6% starch by using Rapid Visco Analyzer (RVA) showed that pasting temperature and setback value of the modified starches decreased by 1–8 °C and 16–59%, respectively, whereas peak viscosity increased by 28–106%, compared to the native starch. Hydroxypropylated starches had lower gelatinization parameters (To, Tp, Tc and ΔH) than those of the native starch. Gelatinization temperature (Tp) of the modified starches was in the range of 60–69 °C, whereas that of the native starch was 70 °C. Hardness value of canna starch gel was considerably lowered by hydroxypropylation. The gel of native canna starch was opaque, whereas that of the hydroxypropylated starches with MS of 0.07 and 0.11 was still clear after being kept at 4 °C for 7 days. Stability of the canna starch to low pH and high shear was insignificantly altered, but freeze-thaw stability was substantially improved by hydroxypropylation.