Effect of sulfate and citrate salts on derivatization of amylose and amylopectin during hydroxypropylation of corn starch

Common corn starch was modified in 0.56 M sodium sulfate solution and in 0. 31 M potassium citrate solution. It was found that about 1.8 times the amou nt of reagent (propylene oxide) was needed to get a same molar substitution (MS) when potassium citrate was used. Hydroxypropylated starches. were fra ctionated on a size-exclusion column to separate amylose from amylopectin, and MS values of the whole starch, the amylose, and the amylopectin were de termined. In all preparations, amylose was derivatized to a greater extent than was amylopectin. The data indicate that, with common corn starch: (1) the greater the overall derivatization, the greater was the preference for derivatization of amylose; and (2) the preference for amylose derivatizatio n was greater for corn starch modified in potassium citrate solution than i n sodium sulfate solution when the MS values for the two preparations were essentially the same. (C) 2000 Elsevier Science Ltd. All rights reserved.