New ¹H NMR Procedure for the Characterization of Native and Modified Food-Grade Starches

Abstract

A novel, fast, and straightforward procedure is presented for the characterization of starch (the largest energy component in food) and modified starches (such as octenyl succinic anhydride (OSA)-modified starches used as a dispersing agent in the food industry). The method uses (1)H NMR to measure the degree of branching and also, for modified starches, the degree of chemical substitution. The substrate is dissolved in dimethyl-d(6) sulfoxide; addition of a very low amount of deuterated trifluoroacetic acid (d(1)-TFA) to the medium gives rise to a shift to high frequency of the exchangeable protons of the starch hydroxyl groups, leading to a clear and well-defined (1)H NMR spectrum, which provides an improved way to determine the degrees of both branching and chemical substitution. Measurements of the size and molecular weight distributions by multiple-detector size exclusion chromatography show that degradation by TFA does not affect the accuracy of the method.