Determination of the level and position of substitution in hydroxypropylated starch by high-resolution H-1-NMR spectroscopy of alpha-limit dextrins

Eleven hydroxypropylated starch samples were thinned by bacterial alpha-amylase at 80 degrees C prior to H-1-NMR analysis on a 400 MHz instrument. Hydroxypropyl (HP) levels were calculated from the intensity of the HP methyl signal (1.18 ppm) compared with that of the methylene and methine (HCO) multiplet (3.2-4.1ppm). HP values determined by H-1-NMR correlated well with those determined by the colorimetric Johnson procedure. Anomeric proton signals in the spectra of alpha-limit dextrins were used to identify the positions of KP substitution. Methyl 2-O-, 3-O- and 6-O-hydroxpropyl-alpha-D-glucopyranosides were synthesized, and only the 2-ether shifted the H-1 signal. Eight HP starches with a molar substitution of 0.05-0.23 had 67-78% HP on O-2, 15-29% on O-3 and 2-17% on O-6. (C) 1997 Academic Press Limited