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

Abstract

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.

Developments in Hydroxypropylation of Starch: A Review

“…Hydroxypropylation also changed the pasting and paste properties of starch, but in a somewhat less consistent manner. Pasting and peak temperatures/times, trough/hot‐paste viscosity, and setback decreased, while peak viscosity and breakdown increased after hydroxypropylation of normal starches, with changes being a function of MS. The effects of hydroxypropylation on the waxy maize starch were considerably less than they were on normal maize starch.…”

“…None of the studies reporting on granule size, shape, and surface characteristics before and after hydroxypropylation used a control, which would be subjecting the starch granules to the same pH, temperature, and type and concentration of salt for the same time used in the modification process to determine if any morphological changes might owe to reaction conditions rather than substitution. Nevertheless, only slight or no erosion of the starch surface following hydroxypropylation has been observed . Size of amylomaize starch granules increased as MS increased, undoubtedly the result of increased swelling.…”

“…Nevertheless, only slight or no erosion of the starch surface following hydroxypropylation has been observed. [25,27,[46][47][48][49][50][51][52] Size of amylomaize starch granules increased as MS increased, [49] undoubtedly the result of increased swelling.…”

“…Almost all reports of investigations of changes in thermal properties report reductions in the onset and peak temperatures (and usually conclusion temperature) and of the enthalpy of gelatinization [25,31,32,38,40,46,47,[48][49][50][51]53,54,[56][57][58][59][60][61][62][63][64][65] as a function of increasing MS. Hydroxypropylation of acid-modified Kudzu root starch produced the same effects. [37] The magnitude of the changes vary for different starches and different degrees of substitution.…”

“…Hydroxypropylation also changed the pasting and paste properties of starch, but in a somewhat less consistent manner. Pasting [10,25,31,46,47,49,55,59,62,63,66,70] and peak [25,26,31,47,55,59,63] temperatures/times, trough/hot-paste viscosity, [25,47,55,[61][62][63] and setback [25,26,46,47,55,59,63,66] decreased, while peak viscosity [10,25,26,31,46,47,55,59,[61][62][63]66] and breakdown [10,25,26,31,47,51,…”