Direct visualization of changes in deacylated Na+ gellan polymer morphology during the sol-gel transition

Abstract

Changes in gellan polymer morphology during the sol-gel transition were directly visualized by transmission electron microscopy and a model incorporating these changes and existing physical data is proposed. Our observations suggest that the most thermodynamically stable conformations of gellan polymers in solution, in the absence of added cations, are the double helix and double-helical duplexes. We have demonstrated two forms of lateral aggregation of gellan helices in the presence of Ca(2+) and K(+) ions. One type forms junction zones that lead to network formation and gelation, while the second type leads to the formation of isolated fibers of aggregated helices and inhibition of gelation. The proposed model of gellan gelation is based on these observations where thermoreversibility, gel strength, and endothermic transitions of gellan gels can be explained.