Mixed Gels Formed with Konjac Mannan and Xanthan Gum

Abstract

Konjac Mannan (KM) is a β-D-(1-4) linked glucomannan and contains 1-3 linked branches occurring at C-3 of glucose and mannose residues. Whereas native KM is soluble in water, deacetylation results in the formation of a thermally irreversible gel. Xanthan gum has a β-D-(l-4) linked glucan backbone with short trisaccharide side-chains consisting of α-D-mannose, β-D-glucuronic acid, and β-D-mannose on alternating glucose residues. Xanthan gum does not form true gels in aqueous solution but it has been shown to undergo a thermally induced conformational change that is sensitive to the presence of electrolyte. Mixtures of xanthan + KM have been reported to form thermally reversible gels and the gels produced are much stronger and have higher melting points than those formed between xanthan and galactomannans. Early work suggested that a specific interaction occurred between the ordered xanthan molecule and the galactomannan or glucomannan chain. M. Tako concluded that intermolecular interaction occurs between the xanthan side chains and the galactomannan backbone and that the molecules adopt the same ordered conformation as in the solid state. G. J. Brownsey suggested that intermolecular binding involves co-crystallization of sections of the disordered xanthan chain with the structurally similar segments of the galactomannan or glucomannan chain. This chapter presents a paper with the purpose to providing further evidence of intermolecular binding between xanthan and KM and to shed further light on the gelation mechanism. It is concluded that KM interacts with xanthan molecules in two different conformational forms.