Direct visualization of the side-by-side self-assembly of high and low acyl gellan gum by AFM

Abstract

This study explores the gelation mechanisms of high and low acyl gellan gum (HAGG and LAGG) by analyzing their chain conformations and self-assembly behaviour during cooling. Using statistical analysis of atomic force microscopy (AFM) images, differential scanning calorimetry (DSC), and rheological measurements, we examined the cooling process from 90 °C to 25 °C for HAGG and from 90 °C to 10 °C for LAGG. Both types of gellan gum transitioned from single-stranded chains to double-helical structures. HAGG exhibited semi-flexible single and double-helical chains with shorter persistence lengths, prominent kinks, and larger kink angles, forming double helices through intra- and interchain interactions. These helices then underwent side-by-side self-assembly into multi-branched, elastic networks. Conversely, LAGG displayed more rigid chains with longer persistence lengths, fewer kinks, and smaller kink angles, forming double helices via interchain interactions, followed by side-by-side self-assembly into less-branched, rigid networks. AFM directly visualized these structural transitions, notably the side-by-side self-assembly for the first time, supported by DSC and rheological data. The results provide new evidence on gellan gum's gelation mechanisms and self-assembly behaviour in pure water.