posted on 2022-10-24, 21:05authored byJenny Fjodorova, Robin Held, Gerd Hublik, Jorge M. Esteban Vazquez, Volker Walhorn, Thomas Hellweg, Dario Anselmetti
Xanthan gum is a polysaccharide that is widely used as
a thickening
agent in numerous food, cosmetic, and technical applications. Therefore,
the knowledge of the molecular interplay that builds up and stabilizes
water-binding networks is crucial for the optimization of xanthan
thickening performance. Using atomic force microscopy, rheometry,
and inductively coupled plasma optical emission spectroscopy, we show
a clear correlation between xanthan thickening properties and the
ability to form characteristic secondary structures as well as the
valence and amount of cations coordinated at the polysaccharide side
chain. Based on these findings and the Debye–Hückel
theory, we derive an ion-interaction model in which divalent cations
mediate bridging of adjacent single polymer strands due to chelate-like
coordination building stable secondary structures. We furthermore
demonstrate in a cation exchange assay that xanthan secondary structures
can be modified in a directed and reversible manner, which, in turn,
alters its thickening properties.