NMR-based identification of thickeners in membrane-filtered food premixtures

Abstract

Premixtures for food production are complex mixtures typically containing thickeners due to their water binding capacity. Here, we report an improved protocol for the fast identification of food thickeners by 1H-NMR spectroscopy. The method is based on four steps: (i) dissolving of the dry premixture in water, (ii) centrifugation of the solution using centrifugal concentrators with a cut-off of 100 kDa, (iii) re-dissolving of the freeze-dried filtrate and the filter residue in small volumes of deuterated water, respectively, and (iv) 1H-NMR analysis of these fractions focusing on specific marker signals. Using this procedure, the high molecular weight thickeners (above 100 kDa) ĸ-carrageenan, galactomannans, gum arabic and pectin were unequivocally identified in the NMR spectra of the filter residues from different premixtures, whereas low molecular substances (below 100 kDa) including sucrose and glucose were determined in the filtrates. Graphical abstract: [Figure not available: see fulltext.].