Xanthan gum (XG) is a water-soluble extracellular polysaccharide that exhibits high viscosity and pronounced shear-thinning behavior. In this study, it was found that an aqueous mixture of unmodified XG and XG modified by high-temperature and high-pressure treatment (autoclaving) forms gels after a heat–cool process. While XG has been known to interact with other polysaccharides such as locust bean gum or glucomannan to form gels, gelation induced by mixing unmodified and modified XG can present a novel mechanism.

Modified XG (XG_AC240) was prepared by autoclaving a 1.5 wt% XG solution at 135 °C for 240 min, followed by precipitation with isopropanol to recover. Molecular weights were determined using the size exclusion chromatography coupled with multiple-angle light scattering, whereas organic acid concentrations were quantified by the post-column detection and high-performance liquid chromatography. Rheological properties for the aqueous mixtures of unmodified and modified XG were examined on a MCR 302 rheometer before and after the heat–cool cycle, which was performed by holding the sample at 80 °C for 10 min, cooling to 10 °C at a rate of 5 °C/min, and maintaining at 10 °C for 180 min prior to the measurement of the frequency dependence of dynamic viscoelasticity in the range of 0.1–100 rad/s. Atomic force microscopy (AFM) observation was carried out using a MultiMode 8-HR in tapping mode on samples prepared by air-drying the aqueous mixtures on a mica surface.

Results showed that XG _AC240 had a lower weight-average molecular weight (approx. 380K) compared to unmodified XG (approx. 1,600K). In addition, pyruvic acid content for XG _AC240 decreased to 1.4 wt% from 5.9 wt% for unmodified XG. Rheological analysis revealed that both 1.5 wt% untreated XG and the mixed system for 0.75% unmodified XG and 0.75% XG_AC240displayed weak-gel type mechanical spectra. The mixed system exhibited lower frequency-dependence of dynamic storage modulus compared to unmodified XG, indicating more solid-like structure for the mixed system. AFM imaged the aggregations between unmodified XG and XG_AC240, forming the supramolecular assemblies.

These findings suggest that the gelation occurs as a result of the supramolecular cluster formation between the two components, and the resulting structure is more likely to be the fractal-like network rather than the homogeneous polymer matrix. To support this hypothesis, circular dichroism spectroscopy is currently being conducted on the modified XG. This study provides new insights into the design of xanthan-based gels through controlled thermal modification, offering potential applications in food and material sciences.