Binding site of xanthan/galactomannan synergistic interaction investigated by NMR

Mixtures of xanthan and galactomannan is one of the most extensively studied synergistic gelling system. A variety of methods were performed, and a plenty of experimental data have been accumulated, but the molecular origin of synergistic interaction has been in dispute in the past 30 years. For example, is the galactomannan really directly bound to xanthan? If so, where is the binding region? We prepared low molecular weight samples to improve NMR spectra, and applied a method, nuclear Overhauser effect (NOE), which is one of the NMR techniques useful for finding the binding region, and found (1) a direct evidence of intermolecular binding of xanthan and galactomannan in semi-dilute region and that (2) the pyruvate group locating at the terminal mannose of side chain in xanthan and the mannose backbone are the binding region. The binding region of locust bean gum is mannose backbone, which was proposed by many papers.