Some physicochemical and rheological attributes of phosphorylated and hydroxypropylated wheat starches

Chemical modification of starch is of the prevalent used methods in order to improve its physicochemical attributes. In this study phosphorylated and hydroxypropylated wheat starches were produced with 0.096 and 2.106% degree of substitution, respectively; and then some of their physicochemical and rheological attributes were studied. The implemented chemical changes due to hydroxypropylation and phosphorylation on native wheat starch were exhibited by FT-IR. X-ray diffraction (XRD) results showed that the native and phosphorylated wheat starches had the most and least amount of crystallinity with 17.34 and 16.14%, respectively. The influence of temperature on swelling power revealed that the native (E_a=46.111) and hydroxypropylated (E_a=26.603) wheat starches had the most and least thermal sensitivity, respectively. Besides, in the case of solubility index, it was observed that native (E_a=77.674) and phosphorylated (E_a=44.478) starches had the most and least thermal sensitivity, in the order given. The high value of determination coefficient (0.895-0.979) attained from the modeling results of the solubility changes with temperature using two power law equations, demonstrated the high capability of these models in prediction. It was seen that hydroxypropylation and phosphorylation of wheat starch resulted in 2.65 times increase and 17.58 times decrease in paste clarity compared to native starch (p<0.05), respectively. Among the used rheological models, the Herschel-Bulkley model was found to be more suitable to predict the flow characteristics of the starch samples.