One of the key functionalities of xanthan gum that set it apart from other hydrocolloid thickeners is its ability to interact synergistically with galactomannans such as guar gum, cassia gum, tara gum and locust bean gum and with structurally similar polysaccharides such as the glucomannan konjac. This interaction results in either a synergistic increase in viscosity in the case of guar gum or the formation of strong self supporting gels as seen with locust bean gum and konjac glucomannan. Initial studies proposed a model in which the unsubstituted, galactose free (smooth) regions of the galactomannans bind to xanthan in its ordered state. This model has been used to explain the difference in degree of interaction between galactomannans of differing degrees of substitution. For example locust bean gum which has a galactose content "of 17 - 26% forms self supporting gels with xanthan gum whereas guar gum which has a galactose content of 33 - 40% forms weak gel networks resulting in a synergistic increase in viscosity. Subsequent studies, which showed that interactions were enhanced after heating the mixture to temperatures above the coil-helix transition of the xanthan, were interpreted as evidence that the binding occurred with the cellulosic backbone of the xanthan gum in the ordered state. An alternative explanation was that when the hydrocolloids are mixed at temperatures below the setting point of the gel, they form an inferior, disrupted network with melting and resetting giving a stronger, coherent gel. More recent studies tend to support this interpretation which favours the original model of Morris et al.
展开▼
