The food industry has shown a strong interest in the widespread adoption of microbial-derived polysaccharides. This is primarily due to the expensive nature of carbohydrate polymers from plant and animal sources and the skilled labor required for extracting them [1]. Xanthan gum (XG), a widely utilized food additive and thickening agent, is a polysaccharide derived from specific strains of the bacterium Xanthomonas campestris [2]. It is commonly produced by a fermentation process for commercial purposes. XG exhibits an anionic structure due to the presence of acetate and pyruvate groups, making it highly amenable to conformational modifications. Additionally, it can form strong intermolecular interactions and multiple helical structures (single, double, and triple helices), creating an intricate network structure [3]. XG is non-toxic and possesses distinctive characteristics, including biodegradability, biocompatibility, water solubility, the ability to form highly viscous solutions even at low concentrations, thermal stability, and stability in acidic and alkaline environments [4]. Xanthan has applications in various industries, such as pharmaceuticals, cosmetics, textiles, agriculture, mineral ore processing, and paper production. In the food industry, it is used as a stabilizer, emulsifier, texture enhancer, and flavor enhancer in salad dressings, bakery products, soups, meat products, and dairy products [5].

XG was classified by the FDA [6] as an additive that can be added directly to foods for human consumption. China and Australia are world leaders in the production of XG. The market is expected to reach a value of 1.2 billion US dollars with a growth rate of 4.5 % between 2019 and 2024 [4]. One of the most significant challenges in commercial xanthan production is the high cost of the fermentation medium, which can be mitigated by using low-cost, sustainable agro-industrial by-products [4,7].

Hydrogels are 3D polymeric structures that form natural configurations with water but absorb and retain other biological fluids. Xanthan is among the most widely used natural polymers [4]. Polyphenol-based hydrogels are created by adding polyphenols to the structure by physical and chemical cross-linking, significantly improving their 3D structure and properties [8]. XG can be easily modified through physical (high-pressure homogenization, the addition of emulsion, blending protein, metal/nonmetal ions), chemical (crosslinking agent), chemo-enzymatic, and plasma irradiation processes due to the presence of abundant hydroxyl and carboxylic groups [9]. Studies on changes in rheological properties of polysaccharides in solution in the presence of phenolic compounds are limited [[10], [11], [12], [13], [14], [15]]. Dridi and Bordenave [16] examined the effect of vanillin, caffeic acid, gallic acid, and epigallocatechin gallate on guar, β-glucans, and xanthan gums.

Wine lees (WL) can be regarded as a viable source of phenolic compounds, owing to the capacity of the yeast employed during the fermentation process to interact with and adsorb these compounds [17]. WL is defined by European Economic Community regulation (No. 337/79) as a residue formed at the bottom of wine containers after fermentation, during storage, or after authorized treatments [18]. Unlike other winemaking residues, WL has a high chemical oxygen demand (>30,000 mg L−1) [19]. This important by-product, discarded during wine production, should be utilized better. The typical composition of red wine lees includes yeast, tartaric acid, phenolic compounds, and other inorganic substances [20]. Felix et al. [17] investigated the combined effects of XG and phenolic compounds on the stability of oil-in-water emulsions. They reported that the addition of WL from white wine to XG helped maintain the stability of the emulsions. Lastra Ripoll et al. [21] studied the rheological properties of XG-based coating solutions enriched with phenolic mango peel extracts. These authors observed that the addition of phenolic extracts showed a dose-dependent increase in the viscosity of the solutions. However, there is limited research on the specific effects of phenolic chemicals on XG. Beyond only reducing the cost of the fermentation medium, XG can be innovatively enhanced by integrating bioactive components produced from agricultural waste. In addition to improving its technological and functional qualities, this method also decreases operational expenses. The use of these agricultural by-products makes XG modification more economically and ecologically sound, providing a double benefit in the form of reduced production costs and a more responsible use of scarce resources.

The primary objective of our study was to improve the structure of XG using WLE (wine lees extract) from red wine, a readily available waste material. The aim was to achieve the desired effect with lower concentrations of XG in a wide range of products, thereby promoting an environmentally friendly and cost-effective approach. For this purpose, the rheological characteristics, water holding, and oil binding capacities of hydrogels were examined, and mathematical modeling was employed to determine the optimal combination of different concentrations of XG and WLE at various cross-linking temperatures. Additionally, the functional properties of hydrogels were determined, and their structural characterization was carried out.