Sichuan pepper, the spice behind the famous numbing tingle of Chinese cuisine, has long been prized for its flavor and its role in traditional medicine. Now, scientists have found a way to squeeze far more value out of the plant’s discarded parts. In a study published in Food Chemistry: X, researchers led by Mengjia Wu and colleagues report that deep eutectic solvents, a new generation of environmentally friendly liquids, can extract health-promoting polysaccharides from the pericarps and leaves of Zanthoxylum bungeanum with yields several times higher than conventional water-based methods. Remarkably, the recovered molecules were not only more abundant but also more biologically potent, and the team went a step further by turning them into functional hydrogels with promising material properties.
The target molecules are plant polysaccharides, long chains of sugars that have attracted growing scientific interest for their antioxidant, anti-fatigue, and immunomodulatory effects. Previous studies have suggested that polysaccharides from Zanthoxylum bungeanum leaves can combat physical fatigue by regulating glycogen metabolism and bolstering the body’s antioxidant defenses, while pericarp polysaccharides have shown antitumor, analgesic, antibacterial, and antioxidant activities in earlier research. The problem has been getting them out of the plant efficiently. Traditional hot water extraction is simple and cheap but slow and energy-hungry, while enzyme-assisted approaches, although gentler, add cost and complicate purification on an industrial scale.
Deep eutectic solvents offer an elegant alternative. These solvents are formed by mixing a hydrogen bond acceptor, such as choline chloride or betaine, with a hydrogen bond donor, such as an organic acid or alcohol. The components lock together through an intricate hydrogen-bonding network to form a homogeneous liquid that is non-volatile, biodegradable, low in toxicity, and highly tunable. By adjusting the chemical identity and molar ratio of the two components, chemists can essentially design a solvent with properties matched to a specific target molecule. That tunability is precisely what the Chinese team exploited in their screening of twelve different solvent systems.
Among the twelve candidates tested under ultrasound assistance, one clear winner emerged: a combination of choline chloride and oxalic acid in a 2:1 molar ratio, designated DES1. Choline chloride is generally recognized as safe and widely used in food and pharmaceutical applications, and oxalic acid is a naturally occurring organic acid. The researchers propose that this particular solvent outperforms its rivals because of stronger electrostatic interactions with the target polysaccharides. The acidic oxalic acid component also appears to promote the hydrolysis of glycosidic linkages in the plant cell wall, loosening the rigid cellulose, hemicellulose, and pectin network that normally locks the polysaccharides in place. Adding 30 percent water reduced the solvent’s viscosity and improved mass transfer, while ultrasound cavitation further battered the cell walls open.
To squeeze the maximum performance out of the winning solvent, the team ran single-factor experiments followed by a rigorous response surface optimization using a Box-Behnken design of seventeen experimental runs. Temperature, extraction time, and solvent-to-solid ratio all mattered, with temperature exerting the strongest influence on yield. Yields climbed as temperatures rose to 80 degrees Celsius but declined beyond that point, likely because heat weakened solvent-solute interactions and degraded heat-sensitive molecules. Extraction times of roughly one hour proved optimal, with longer sonication apparently degrading the polysaccharides, and a solvent-to-solid ratio of about 70 milliliters per gram gave the best recovery. The statistical models fitted the data impressively well, accounting for more than 98 percent of response variability.
The verified results were striking. Under optimized conditions, the deep eutectic solvent extracted 25.88 percent polysaccharide by weight from pericarps and 29.79 percent from leaves, matching the model predictions almost exactly. When plain deionized water was substituted under otherwise identical ultrasound-assisted conditions, yields fell to just 6.27 percent and 12.13 percent respectively. That translates to a 4.13-fold improvement for pericarp polysaccharides and a 2.46-fold improvement for leaf polysaccharides over the aqueous control, and a clear advantage over previously reported ultrasound-assisted water extraction of pericarp polysaccharides, which had peaked at around 14 percent. The higher leaf yield likely reflects the thinner, less lignified cell walls of leaf tissue compared with the tougher protective pericarp.
Structural analysis showed that the solvent-extracted and water-extracted polysaccharides share the same basic building blocks. High-performance liquid chromatography after acid hydrolysis revealed that all four samples contained mannose, rhamnose, glucuronic acid, galacturonic acid, glucose, galactose, xylose, and arabinose, with glucose and galactose dominating and pointing to abundant arabinogalactan and glucan components. Infrared spectroscopy confirmed characteristic polysaccharide features, including hydroxyl stretching, esterified and non-esterified carboxyl groups, and pyranose ring vibrations. Crucially, however, the deep eutectic solvent samples carried higher ratios of glucuronic to galacturonic acid, suggesting the acidic solvent selectively enriches uronic acid-rich, negatively charged polysaccharide fractions.
That subtle structural shift appears to translate directly into biological performance. In radical scavenging assays, the solvent-extracted polysaccharides dramatically outperformed their water-extracted counterparts against hydroxyl radicals, one of the most damaging reactive oxygen species in living systems. The concentration needed to neutralize half of the hydroxyl radicals was just 0.231 milligrams per milliliter for pericarp polysaccharides and 0.513 for leaf polysaccharides, compared with 2.385 and 2.701 for the water-extracted versions, and at 2 milligrams per milliliter the solvent-extracted pericarp polysaccharides quenched over 95 percent of hydroxyl radicals. The pattern reversed for ABTS radicals, where water-extracted samples fared better, suggesting the two extraction methods selectively preserve or enrich subfractions operating through different radical-quenching chemistries, hydrogen atom transfer in the acidic solvent environment versus single electron transfer in water.
As a proof of concept, the team then folded the potent solvent-extracted polysaccharides into chitosan hydrogels crosslinked with citric acid. Scanning electron microscopy revealed dense, regular three-dimensional pore networks, with the leaf polysaccharide hydrogel reaching an average pore size of 97.6 micrometers. The composite gels swelled to roughly 1200 percent of their dry weight, far exceeding the blank chitosan gel, and achieved polysaccharide loading efficiencies of about 68 to 70 percent. Encouragingly, both hydrogels passed a basic hemocompatibility test, keeping hemolysis below the standard 5 percent safety threshold at loading concentrations of up to 2.0 and 4.0 milligrams per milliliter. Although immobilization in the gel network modestly reduced radical scavenging relative to free polysaccharides, the gels retained substantial antioxidant activity.
The authors are candid about the limits of their work: the polysaccharide structures were characterized only at a preliminary level, deproteinization efficiency was not quantitatively verified, and the hydrogels have yet to face cytotoxicity, antimicrobial, or in vivo wound healing tests. Residual solvent components and co-extracted phenolics could also contribute to the measured antioxidant effects, and rigorous purification and control experiments will be needed to attribute activity purely to the polysaccharides themselves. Even so, the study delivers a powerful demonstration that designer green solvents can do far more than replace hazardous chemicals. They can chemically tailor what they extract, boosting both quantity and quality, and turn an agricultural by-product into a platform for functional biomaterials. For a spice industry that discards tons of pericarps and leaves each year, that tingle of opportunity is hard to ignore.
Subject of Research: Green extraction of bioactive polysaccharides from Zanthoxylum bungeanum using deep eutectic solvents and their hydrogel applications
Article Title: Green extraction of bioactive polysaccharides from Zanthoxylum bungeanum using deep eutectic solvents: enhanced yield, antioxidant activity, and functional hydrogel formation
Article References: Wu, M., Yu, G., Hu, W., Liu, Y., & Liu, Y. (2026). Green extraction of bioactive polysaccharides from Zanthoxylum bungeanum using deep eutectic solvents: enhanced yield, antioxidant activity, and functional hydrogel formation. Food Chemistry: X, Article 104612. https://doi.org/10.1016/j.fochx.2026.104612
Image Credits: AI Generated
DOI: Not provided
Keywords: deep eutectic solvents, Zanthoxylum bungeanum, polysaccharides, green extraction, antioxidant activity, hydrogels, Sichuan pepper, ultrasound-assisted extraction, response surface methodology, chitosan, biomaterials, food chemistry
News Source: Bethany Barker. (October 14, 2026). Green Solvents Unlock Powerful Antioxidants from Sichuan Pepper Waste. Scienmag.
