Xanthan double-stranded chains

The native sample E (Fig. 3) contains a relatively large amount of aggregated structures. Most of them appear to rearrange into perfectly matched double-stranded chains after incubation at 80 °C for 2 months (27). This rearrangement is reported to result in a fivefold increase in the apparent viscosity at a shear rate of 1 s-1 (27). A similar rearrangement of xanthan assemblies is also observed in a unpasteurized fermentation broth after exposure of the sample... 

Xanthan gum includes D-glucosyl, D-mannosyl, and D-glucuronyl acid residues together with 0-acetyl and pyruvyl residues [4]. The content of pyruvic acid varies substantially based on the species, which in turn leads to varying viscosities of xanthan solutions. Xanthan is considered to assume rigid double-strand helical conformation in its native form [85], with side chains positioned parallel to the helix axis and stabilizing the structure [24]. In solutions, the helical structure turns into flexible coils [85]. 

Figure 2.8. Model proposed by Holzwarth and Prestridge (1977) to explain their electron microscopy observations on xanthan. The section of native xanthan is thought to denature into shorter strands because of breaks in one or other chain of the double helix. The renaturing process is a reverse procedure but imperfections arise during the reassembly, causing small hockles , as shown in the renatured molecule.

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