Effect of chemical modifications on thermal, rheological and morphological properties of yellow sorghum starch.

Starch isolated from yellow sorghum grains was subjected to chemical modifications like acetylation, hydroxypropylation and benzylation. Proximate compositions of these, such as crude protein, crude fat, moisture content and ash content were determined. The effects of modifications on thermal, rheological and morphological properties of yellow sorghum starch were investigated. Differential Scanning Calorimetry studies showed that the gelatinization temperature and enthalpy of modified yellow sorghum starches decreased when compared to that of native starch. The results showed that peak, hot pasting, final, breakdown and setback viscosities were significantly reduced except in hydroxypropylated starch that showed increase in breakdown and setback viscosities. Scanning electron microscopy pictures showed that the modified starch granules had disrupted surfaces compared to native starch granules; hydroxypropylated starch showed the presence of slight fragmentation and a distinct groove in their central core region. The extent of granule disruption was observed to be higher for hydroxypropylated starch than other modified starches.