1998 Volume 49 Issue 9 Pages 985-992
The physical properties of double-modified (hydroxypropylated (HP) and cross-linked) wheat starch and unmodified starch were compared. Three wheat starch samples differing in the degree of modification were used. The properties measured were the granule size distribution, X-ray diffraction, thermal characteristics, swelling power and solubility, transmittance, viscosity, texture, dynamic viscoelasticity, and Hunter whiteness of the gel.
The average granule size of the modified wheat starch with a low degree of substitution was greatest, while that of the unmodified starch with a high degree of substitution was least, suggesting that the difference depended on the starting starch and perhaps not on any modification.
The three hydroxypropylated samples became pasted about 9 t below the unmodified wheat starch, and required less pasting energy.
The HP wheat starch showed increased swelling and solubility below 80°C but these parameters decreased above 80°C Differences in swelling and solubility above 80 °C may have been attributable to differences in cross-linking.
The viscosity-rise onset temperature of each HP wheat starch was lower by about 20°C than that of the unmodified wheat starch. One HP starch showed the highest maximum viscosity and the largest setback, which is consistent with less HP substitution and a low degree of cross-linking.
Each HP wheat starch paste had high cohesiveness, showing an inner binding force higher in the HP starch samples than in the unmodified wheat starch. The gel from the HP wheat starch with the highest pasting curve was firm and non-sticky, while the other two gels tended to be soft and sticky. A firm gel would be expected with a low degree of modification.
Dynamic rheometry of the gels (the starch concentration was 12%) showed that, in general, each the HP wheat starch gel had a lower storage modulus than that of the unmodified wheat starch.
Hunter whiteness measurements show that the HP wheat starch gel had high clarity, two of the HP starch samples being transparent.
