Level and position of substituents in cross-linked and hydroxypropylated sweet potato starches using nuclear magnetic resonance spectroscopy

Using 1H NMR the molar substitution of hydroxypropylation was determined to be 0.155-0.165. The hydroxypropylation predominantly occurred at O-2 (61%), and the level of substitution at O-6 (21%) was slightly higher than that at O-3 (17%). In dual modified starch, the preceding cross-linking procedure resulted in a slightly lower level of hydroxypropylation, where the substitution at O-6 decreased more compared to the substitution at O-2 and O-3.