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 alph a-amylase at 80 degrees C prior to H-1-NMR analysis on a 400 MHz instr ument. Hydroxypropyl (HP) levels were calculated from the intensity of the HP methyl signal (1.18 ppm) compared with that of the methylene a nd methine (HCO) multiplet (3.2-4.1ppm). HP values determined by H-1-N MR correlated well with those determined by the colorimetric Johnson p rocedure. Anomeric proton signals in the spectra of alpha-limit dextri ns 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 a nd 2-17% on O-6. (C) 1997 Academic Press Limited