An improved method to determine the hydroxypropyl content in modified starches by 1H NMR

Hydroxypropyl (HP) starches are used as thickeners and stabilizers in foods. The properties of the etherified starches are dependent on the degree of hydroxypropylation. The objective of this study was to develop an improved acid hydrolysis method to degrade and solubilize HP starches for determining HP content in modified starches by H-1 NMR. The effects of acid (DCl) concentration and temperature on hydrolysis and solubilization of hydroxypropylated starches were examined. The optimal conditions proposed to hydrolyze HP starches were 10% starch solid content, 3.5% (wt%) DCl in D2O as the solvent, sodium acetate as an internal standard, and heating at 90 degrees C for 1 h. Optionally, 6% (v/v) TFA-d may be added as the water-peak shifting reagent. Six hydroxypropylated starches and two cross-linked and hydroxypropylated starches were hydrolyzed with this improved acid method, and the results of the HP content were in agreement with those from an enzyme-catalyzed method.