Quantification of food polysaccharide mixtures by ¹H NMR

Polysaccharides are food ingredients that critically determine rheological properties and shelf life. A qualitative and quantitative assessment on food-specific polysaccharide mixtures by ¹H NMR is presented. The method is based on the identification of intact polysaccharides, combined with a quantitative analysis of their monosaccharide constituents. Identification of the polysaccharides is achieved by ¹H NMR line shape fitting with pure compound spectra. The monomeric composition was determined using the Saeman hydrolysis procedure, followed by direct monosaccharide quantification by ¹H NMR. In the quantification, both the monosaccharide degradation during hydrolysis, as well as a correction for the non-instantaneous polysaccharide dissolution were taken into account. These factors were particularly important for the quantification of pectins. The method showed overall good repeatability (RSD_r=4.1±0.9%) and within-laboratory reproducibility (RSD_R=6.1±1.4%) for various food polysaccharides. Polysaccharide mixtures were quantitatively resolved by a non-negative least squares estimation, using identified polysaccharides and their molar monosaccharide stoichiometry as prior knowledge. The accuracy and precision of the presented method make it applicable to a wide range of food polysaccharide mixtures with complex and overlapping ¹H NMR spectra.