Factors influencing the properties of hydroxypropylated potato starches

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Starches separated from four potato cultivars were hydroxypropylated and their physico-chemical, morphological, thermal and rheological properties were compared. The extent of hydroxypropylation measured as molar substitution differed significantly among the starches from different potato cultivars. Kufri Jyoti hydroxypropylated starch showed highest molar substitution, while Kufri Chandermukhi hydroxypropylated starch showed the lowest. The hydroxypropylated starches showed higher swelling power, solubility, solubility in dimethyl sulphoxide (DMSO) and paste clarity than their counterpart native starches. Light transmittance of hydroxypropylated starches did not change significantly during refrigerated storage while a substantial decrease in the same was observed for native starches. SEM pictures showed that the hydroxypropylated starch granules from all the potato cultivars differed in shape and size from the native starch granules, and showed the presence of slight fragmentation and a distinct groove in their central core region along the longitudinal axis. Hydroxypropylation treatment showed more pronounced effect on large size granules than small size granules. The extent of granule disruption was observed to be higher for hydroxypropylated starch gels that later developed numerous rod shaped or fuzzy clustered microfibrils with diameters ranging from 15 to 20 μm, after 30 days of refrigerated storage. The studies on the phase transitions associated with gelatinization of starches showed lower gelatinization parameters ( T o, T p, T c, and Δ H gel) among the hydroxypropylated starches in which Kufri Jyoti and Kufri Sindhuri starches were the most affected. Hydroxypropylated potato starches exhibited higher peak G′, G″ and lower tan δ during rheological measurements on the dynamic rheometer. Whereas the native starches did not possess freeze-thaw stability, upon hydroxypropylation there was a pronounced decrease in the tendency towards syneresis.