Abstract:
Starches isolated from rhizomes of two cultivars of edible canna (namely;Thai-green and Thai-purple) were hydroxypropylated with propylene oxide at 40 ?C and pH 5.5 in order to reduce retrogradation and increase gel stability. The extent of hydroxypropylation measured as molar substitution (MS) were 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, were used. Scanning electron micrographs showed that the granular size and shape of the modified starches were similar to those of the native starch. The canna starch granules were characterized as a B type X-ray diffraction pattern. Investigation on pasting properties of 6% starch by using Rapid Visco Analyzer showed that pasting temperature and setback value of the modified starches decreased whereas peak viscosity increased, compared to
native starch. Hydroxypropylated starches had lower gelatinization parameters and enthalpy (?H) than the native starch. Gelatinization temperature (Tp) of the modified starches was in the range of 60-69 ?C where that of the native starch was 70 ?C. Hardness values of hydroxypropylated starch gels were considerably lower than that of the native starch gel. Stability of the canna starch to low
pH and high shear was insignificantly altered, but freeze-thaw stability was substantially improved by hydroxypropylation. Similar effect of hydroxypropylation on physicochemical properties of the Thai-purple starch was found. Paste and gel properties of the hydroxypropylated canna starch were
better/comparable to the commercial starches.