Analysis of Hydroxypropyl Starch
Corn starch is modified by hydroxypropylation for food applications. The modification helps keep the starch viscous for gravys, puddings, etc.
We dissolve about 5 mg of the sample in D2O slightly acidified. We run our 1H spectrum at 85 C suppressing the water peak at 4.30ppm. The starch spectrum is shown on the next page.
We can determine the level of hydroxpropylation by integrating the signals from the methylgroup 1.20ppm vs the signals from the anomeric H's from 5.8 to 4.5ppm. Notice that the later group of signals includes those from the reducing endgroups and from the 1-6 connections. ( The amylopectin in starch contains 1-6 as well 1-4 glucosides.) Values range from 5% to 12% propylene oxide, dry solids basis. .