Solution Structure of Molecular Associations Investigated Using NMR for Polysaccharides: Xanthan/Galactomannan Mixtures

Abstract

Although the intermolecular nuclear Overhauser effect (NOE) signal was valuable to elucidate molecular association structure, it could not always be observed for associated molecules due to the short spin-spin relaxation time T2 in NMR measurements, especially for high molar mass systems. While almost no study has been reported for high molar mass polymers (>1 × 10(6)), especially for polysaccharide-polysaccharide interactions, NOE signals were observed for the first time between two different types of polysaccharides, xanthan and galactomannan (locust bean gum), forming a synergistic gel, as a direct evidence of intermolecular binding of polysaccharides. The NOE peak was found between pyruvic acid in xanthan and anomeric proton of mannose of galactomannan. This NOE signal was observed only when mixing time >0.5 s, indicating indirect NOEs caused by spin diffusion. Therefore, this NOE could not be used to construct the molecular models. However, it is a direct evidence for the binding between two different types of polysaccharide to elucidate the synergistic gelation. This NOE signal was observed only for low molar mass galactomannans (1.4 × 10(4)). T2 of pyruvate methyl drastically decreased at low temperatures in the presence of synergistic interaction, suggesting that pyruvate group at terminal end of side chain in xanthan plays an essential role in synergistic interaction.

Hydrophobized cellulose nanocrystals enhance xanthan and locust bean gum network properties in gels and emulsions

“…The enhancement of the hydrophobe retention was attributed to an increase in local hydrophobicity due to interactions of XG side chains with smooth (unsubstituted) segments of LBG (Grisel et al, 2015). Additionally, NMR studies demonstrated motional restrictions of the XG pyruvate group in the presence of LBG (Takemasa & Nishinari, 2016), which confirms involvement of this hydrophobic moiety at the terminal end of XG side chains in the intermolecular interactions between XG and LBG. This implies that the structural and rheological properties of LBG/XG mixtures can be further modified with moderately hydrophobic additives.…”

“…It is hypothesised that smooth (unsubstituted) segments of the LBG macromolecules interact with the side chains of XG molecules. There is specific evidence that the pyruvate group at the terminal end of the xanthan side chain is involved in this interaction (Takemasa & Nishinari, 2016). The introduction of both hydrophilic and hydrophobized CNCs into the LBG/XG synergistic gel led to significant changes of the viscoelastic properties, with a greater increase in the elastic modulus observed for hydrophobized CNCs.…”

Locust Bean Gum, a Vegetable Hydrocolloid with Industrial and Biopharmaceutical Applications

“…Different authors tried to explain where these interactions take place: between side chains of xanthan helices and smooth regions of the galactomannan backbones [ 95 ], between the xanthan helix and those smooth regions [ 96 ], or between the disordered xanthan and galactomannan structures [ 97 ]. Respectively, those possible scenarios are called the “Tako model”, the “Unilever model” and the “Norwich model”, as described by Takemasa and Nishinari ( Figure 3 ) [ 98 ].…”

“… Different models of Xanthan Gum—Galactomannan synergies [ 98 ]: ( a ) Unilever model [ 99 ], ( b ) Norwich model [ 100 ], ( c ) Tako model [ 101 ] (G, galactomannan; X, xanthan gum). …”

The Food Colloid Principle in the Design of Elderly Food

“…According to Morris (), a common feature for synergistic interaction is as follows: (1) One polysaccharide undergoes coil‐helix conformational transition, such as agarose, carrageenan, furcellaran, gellan and xanthan gum; (2) The backbone linkage of the other polysaccharide in the mixture is β(1,4) linkage, such as in konjac glucomannan or galactomannan or xyloglucan. Takemasa recently elucidated the mechanism of the synergistic interaction using nuclear overhauser effect (NOE), and excluded the gelation model for mixed polysaccharides based on phase separation (Takemasa and Nishinari ).…”