A fibrous model for gellan gels from atomic force microscopy studies

Abstract

Atomic force microscopy has been used to investigate the mechanism of gelation and the nature of the long-range molecular structure in gellan gum gels. Gellan gum has been studied as a model for thermoreversible polysaccharide gels. Images have been obtained of aggregates, gel precursors, aqueous films and bulk 3D aqueous gels. In the absence of gel-promoting cations helix formation leads to the formation of elongated partly branched filaments. These filaments are of constant height and width, and association appears to involve just helix formation, without side-by-side aggregation of the helices. In the presence of the gel-promoting cation potassium gel precursors consisting of branched fibres of variable height and width are formed. These are believed to arise from side-by-side aggregation of the helical filaments. Similar branched fibrous structures have been observed forming the network structures of aqueous gellan films or 3D gels. The gel structure is seen to be a continuous branched network. There are no discrete junction zones: rather cation binding and helix association is continuous throughout the network.