- Xanthan is an extracellular polysaccharide produced by the bacterium Xanthomonas campestris, a plant-pathogenic microorganism. It is one of the most widely used microbial polysaccharides, valued for its unique rheological and stabilizing properties.
- Structurally, xanthan is a heteropolysaccharide composed of a cellulose-like backbone of β-(1→4)-linked D-glucose units, to which trisaccharide side chains are attached. These side chains typically consist of mannose–glucuronic acid–mannose, with varying degrees of acetylation and pyruvylation. The presence of charged groups, such as carboxyl groups from glucuronic acid and pyruvate, imparts xanthan with a polyanionic character, which greatly influences its solubility, viscosity, and interaction with ions and other polymers.
- One of xanthan’s most notable features is its ability to produce highly viscous solutions at low concentrations. It is a pseudoplastic polymer, meaning its viscosity decreases under shear stress but recovers once the stress is removed. This shear-thinning property makes xanthan ideal for applications where controlled flow is needed, such as in salad dressings, sauces, and cosmetics. Unlike many other polysaccharides, xanthan maintains its viscosity over a broad range of temperatures, pH values, and salt concentrations, giving it exceptional stability under diverse processing conditions.
- In nature, xanthan functions as a protective extracellular matrix for Xanthomonas, contributing to biofilm formation and enhancing bacterial survival on plant surfaces. Its ability to retain water and form viscous solutions also helps protect the bacteria against desiccation and host defense mechanisms. From an industrial perspective, xanthan is produced through microbial fermentation using carbohydrate feedstocks such as glucose or sucrose, followed by recovery and purification of the polymer. Its microbial origin ensures a sustainable and scalable supply, making it one of the earliest biopolymers to be produced commercially at large scale.
- The applications of xanthan are diverse and span multiple industries. In the food industry, it is widely used as a thickener, stabilizer, and suspending agent in products ranging from dressings and sauces to beverages and gluten-free baked goods. In the pharmaceutical and biomedical fields, xanthan is employed in drug delivery systems, controlled-release formulations, and as a component of hydrogels and wound dressings, owing to its biocompatibility and ability to form stable gels. In the oil industry, xanthan is used in enhanced oil recovery and drilling fluids, where its viscosity and salt tolerance improve fluid performance under extreme conditions. It also finds uses in cosmetics, agriculture, and biodegradable materials research.
- From a scientific perspective, xanthan continues to be of interest due to its unique molecular conformation and rheological behavior. In solution, xanthan chains adopt a stiff helical structure stabilized by intramolecular hydrogen bonds, which contributes to its high viscosity and stability. Its interactions with other biopolymers, such as guar gum or locust bean gum, can produce synergistic effects, enhancing gel formation and thickening properties. Such interactions expand its range of functionality and have been exploited in food and pharmaceutical formulations.
