Influence of reaction conditions on MS values and physical properties of waxy maize starch derivatized by reaction with propylene oxide

Waxy maize starch was hydroxypropylated under different swelling conditions (pH, temperature, salt type, salt concentration) to determine the effect of reaction conditions on the extent of modification. MS, pasting temperatures, and paste characteristics of the products were determined. pH had the greatest effect on the extent of reaction. MS values increased as the pH was raised from 10.7 to 11.7. In most cases, samples hydroxypropylated in the presence of NaCl had lower or equal MS values as compared to those reacted in the presence of Na2SO4, and reactions carried out in the presence of NaCl were more sensitive to changes in pH than were those conducted in the presence of Na2SO4. The lower MS values for samples reacted in the presence of NaCl was most notable at the lowest pH value. Temperature had less effect on reaction efficiency. No substantial differences were found in pasting temperature or peak viscosity. Under conditions that promoted greatest swelling, viz. highest pH (11.7) and highest temperature used (54 °C), some granules reacted in the presence of NaCl gelatinized, i.e. NaCl failed to prevent pasting. Therefore, it was confirmed that Na2SO4 better protects against gelatinization than does NaCl. The concentration of Na2SO4 (0.395 vs. 0.527 m) only slightly affected MS values.