Influence of reaction conditions on the location of reactions in waxy maize starch granules reacted with a propylene oxide analog at low substitution levels

A constant amount of an anionic propylene oxide analog was reacted with waxy maize starch under conditions in which temperature, pH, and swelling-inhibiting salt type and concentration were varied. Reaction sites were located utilizing a reflectance confocal laser scanning microscopy (R-CLSM) method. Results confirm that uniformity of reaction within granules and molar substitution (MS) levels are a function of reaction conditions. In most cases, increasing pH from 10.7 to 11.7 increased the extent of reaction. Changes in temperature between 44 and 54 °C had little effect. Reactions carried out in the presence of NaCl produced more derivatization than did reactions carried out in the presence of Na2SO4 under identical conditions. More reaction was observed in the presence of a lower concentration (0.395 m) of Na2SO4 as compared to a higher concentration (0.527 m). Salt concentration effects were not discernible when reactions were done in the presence of NaCl (0.471 and 0.629 m).