RESUMO
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 (RSDr=4.1±0.9%) and within-laboratory reproducibility (RSDR=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.
