Xylanase itself is a fascinating target. The enzyme, classified as endo-1,4-beta-xylanase (EC 3.2.1.8), specifically attacks xylan, the complex polysaccharide that ranks as the second most abundant polymer in nature after cellulose and forms a major structural component of plant cell walls. By cutting the beta-1,4-glycosidic bonds threaded through xylan chains, the enzyme releases xylose and xylooligosaccharides, sugars with enormous commercial value. Xylanases are sorted by the carbohydrate-active enzymes database into glycoside hydrolase families, with GH10 and GH11 by far the best characterized; their members differ subtly in substrate specificity, catalytic mechanism, and optimal operating conditions, which in turn shapes their industrial niches. In food processing, xylanases modify the water-binding behavior of bread dough, increasing loaf volume and improving crumb structure, while in animal feed they reduce the viscosity of non-starch polysaccharides to boost nutrient absorption. Beyond food, the same enzyme pre-bleaches kraft pulp in the paper industry and helps open up lignocellulosic biomass for bioethanol production.

The enzyme is sourced from an impressively diverse biological roster. Bacterial genera such as Bacillus, Streptomyces, and Clostridium produce xylanases prized for their thermal and pH robustness — Bacillus species in particular yield thermostable variants suited to high-temperature processing. Fungal producers, including Aspergillus, Trichoderma, and Penicillium, dominate food and feed applications thanks to their efficiency at degrading complex xylans. Plants make xylanases during germination and fruit ripening, and certain herbivorous insects and termites harbor gut microbes that degrade plant cell walls with the enzyme’s help, though plant and animal sources remain marginal industrially. Recombinant DNA technology now allows xylanase genes to be cloned and expressed in hosts such as Escherichia coli and Pichia pastoris, multiplying yields far beyond what natural fermentation achieves. Even so, free enzymes remain fragile in industrial reactors, which is precisely where immobilization — attaching the enzyme to a solid support — enters the picture, a concept dating back to 1916 when charcoal-embedded invertase was first shown to hydrolyze sucrose.

Metal-organic frameworks emerged in the late 1990s as a new class of crystalline solids built from metal ions or clusters coordinated to organic linkers into extended, lattice-like networks. Their defining feature is porosity taken to an extreme: some MOFs boast surface areas exceeding 7000 square meters per gram, among the highest of any known material, offering a vast internal landscape for hosting guest molecules. Just as importantly, MOFs are programmable. By swapping metal nodes and organic struts, chemists can tune pore size, pore shape, and surface functionality with a precision unavailable to conventional carriers such as chitosan beads, alginate gels, or polyaniline films. Synthesis routes are equally varied, ranging from conventional hydrothermal heating under pressure to solvent-free mechanochemical grinding, electrochemical deposition on electrodes, and rapid microwave-assisted growth that produces highly crystalline particles in a fraction of the usual time.

For xylanase, the review highlights several standout MOF platforms. Manganese-doped ZIF-67, a zeolitic imidazolate framework, was used in a comparative study to immobilize xylanase via an in-situ method, with striking results. Encapsulated xylanase retained 85.7 percent of its activity after two hours at 70 degrees Celsius, while the free enzyme plummeted to 28.7 percent. Both the standard and manganese-doped versions kept more than 70 percent of their initial activity through eight consecutive reaction cycles, and the doped variant showed the highest substrate affinity. Functionalized UiO-66-NH2, a zirconium-based framework, served as the scaffold for co-immobilizing beta-xylosidase and endoxylanase, a pairing that maintained over 95 percent relative activity at 95 degrees Celsius in a 50 percent acetone solution and halved the enzyme’s Km value, indicating markedly improved substrate binding. A magnetic Fe3O4@polydopamine@MOF composite achieved protein loading of 80.67 milligrams per gram through multipoint interactions while tolerating both acidic and alkaline conditions.

The immobilization chemistry itself spans a spectrum of strategies, each with distinct trade-offs. Physical adsorption, the simplest approach, relies on weak van der Waals forces, hydrogen bonds, and electrostatic attraction to tether the enzyme to the MOF surface, preserving the protein’s native structure but risking gradual leaching into the product. Covalent bonding forms durable chemical links between amine, carboxyl, or thiol groups on the enzyme and complementary groups on the framework, essentially eliminating leaching at the cost of more elaborate preparation and occasional active-site interference. In-situ encapsulation is arguably the most elegant: enzyme molecules are trapped inside the growing MOF crystal as it assembles around them, creating a protective environment from which escape is nearly impossible. Covalent cross-linking with bifunctional reagents builds a stable enzyme network throughout the pores and across the surface, boosting resistance to harsh conditions. In one demonstration, beta-xylosidase cross-linked onto FeSO4-chitosan-encapsulated MOF microparticles retained 40 percent activity after ten reuse cycles and functioned at temperatures five degrees higher than the free protein, with double the activity at 70 degrees.

Real-world food applications are already validating the concept. A xylanase from a novel Bacillus pumilus strain, immobilized on the copper-based framework Cu-BTC, clarified pineapple and pomegranate juices with enhanced catalytic efficiency and remarkable durability, retaining 61 percent of its activity after 21 cycles. In apple juice trials, Xyl@ZIF-67 raised juice transmittance from 65.61 to 94.73 percent within an hour of treatment, while the manganese-doped version lifted it from 77.80 to 84.13 percent, simultaneously increasing reducing sugar content. Xylooligosaccharide production — a booming market for prebiotic ingredients that selectively nourish beneficial Bifidobacteria and Lactobacilli in the human gut — has proven equally receptive. The magnetic Fe3O4@PDA@MOF-xylanase system converted corncob xylan into xylooligosaccharides at a 23 percent yield, outperforming the free enzyme by a factor of 1.15, while a green-synthesized Xy-Cu-BTC composite achieved an 87.4 percent conversion yield, boosting xylopentose output and suppressing unwanted xylose formation to just 0.88 percent of the product mix.

Challenges remain, and the review does not gloss over them. Leaching persists whenever weak non-covalent interactions are disrupted by shifts in pH, ionic strength, or temperature. Mass-transfer limitations loom large because xylan is a bulky, high-molecular-weight polymer; if MOF pore apertures are too narrow, substrate chains simply cannot reach the immobilized active sites, dragging down reaction rates compared with free enzyme. Aqueous stability is a further concern, as water molecules can competitively displace organic linkers from metal centers, collapsing some frameworks — a problem researchers counter by turning to chemically robust series such as ZIF and MIL frameworks, which simultaneously act as a molecular corset restricting protein unfolding. Food safety adds a final layer of scrutiny: frameworks built from toxic metals such as chromium or cobalt risk contaminating food matrices, so current research favors biocompatible MOFs assembled from iron, zinc, or calcium nodes with Generally Recognized as Safe ligands such as amino acids or citric acid, validated by rigorous leaching assays in food-simulating solvents.

The path forward, the review concludes, lies in hierarchical pore engineering that integrates mesopores large enough for xylan polymers, a transition to aqueous green synthesis routes, and continuous-flow biocatalysis in packed-bed reactors for pulp, bioethanol, and food production. The economics, too, must balance out: MOF supports cost more upfront than silica or chitosan, a premium justified only if exceptional reusability and extended enzyme half-life reduce replacement frequency and simplify downstream recovery. With the immobilized enzyme market projected to reach USD 27.29 billion by 2031 at a compound annual growth rate of 9.45 percent, the commercial incentive to solve these problems is unmistakable. If MOF-encapsulated xylanase delivers on its laboratory promise at industrial scale, the crystal cages now being grown around this humble enzyme could quietly reshape how the world’s food — from breakfast juice to prebiotic supplements — is made.

Subject of Research: Metal-organic framework composites for xylanase enzyme immobilization and their applications in the food industry

Article Title: Metal organic framework composites for xylanase immobilization and their applications in food industry

Article References: Jana, U. K. (2026). Metal organic framework composites for xylanase immobilization and their applications in food industry. Discover Industrial Chemistry and Materials, 1(1), Article 9. https://doi.org/10.1007/s44508-026-00011-0

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00011-0

Keywords: metal-organic frameworks, xylanase, enzyme immobilization, biocatalysis, xylooligosaccharides, fruit juice clarification, ZIF-67, UiO-66-NH2, food safety, prebiotics, nanobiotechnology, food industry

Sorghum, or Sorghum bicolor, is one of the world’s most important cereal crops, particularly across semi-arid regions of Asia and Africa, and its cultivation generates vast quantities of lignocellulosic stalk residue. Like most agricultural biomass, sorghum stalks consist of three principal structural polymers: cellulose, hemicellulose, and lignin. The hemicellulose fraction is dominated by xylan, a long-chain polysaccharide composed of xylose units linked by beta-1,4-glycosidic bonds. When xylan is partially cleaved into short chains of two to ten xylose units, the resulting molecules are known as xylooligosaccharides, or XOS. These compounds have attracted growing commercial interest because they resist digestion in the upper gastrointestinal tract and instead serve as selective substrates for probiotic microorganisms such as Lactobacillus and Bifidobacterium species, a property that defines their function as prebiotics.

The research team, led by Nisha Nisha, Sumit Arora, and Richa Singh of the Dairy Chemistry Division at ICAR-National Dairy Research Institute in Karnal, together with collaborators from the Indian Council of Agricultural Research in New Delhi and the Global Centre of Excellence on Millets at ICAR-Indian Institute of Millets Research in Hyderabad, began by extracting xylan from sorghum stalk biomass using alkaline treatment. The choice of alkaline extraction is chemically deliberate: sodium hydroxide disrupts ester bonds that crosslink xylan to lignin, releasing the hemicellulose fraction in a relatively pure form. The team systematically varied the concentration of sodium hydroxide and found that increasing alkalinity significantly enhanced xylan recovery. The optimal condition, 3 M sodium hydroxide, achieved an xylan recovery of 87.17 percent with a standard deviation of only 0.32 percent, a striking yield for a lignocellulosic feedstock.

Purity was confirmed through Fourier-transform infrared spectroscopy, or FTIR, a technique that identifies functional groups within a material by measuring the absorption of infrared light at characteristic wavenumbers. The spectra indicated that xylan extracted at the highest alkaline concentration contained minimal residual lignin, which matters considerably because lignin contamination can impede subsequent enzymatic reactions and compromise the quality of the final product. By cleaving the chemical associations between xylan and lignin, the alkaline pretreatment effectively liberated a substrate clean enough for precise enzymatic hydrolysis.

The second stage of the process converted the extracted xylan into short-chain oligosaccharides using enzymatic hydrolysis, a reaction catalyzed by xylanase enzymes that cleave the internal beta-1,4 bonds of the xylan backbone. Rather than relying on trial and error, the researchers applied formal statistical optimization using Design-Expert software, which allows multiple reaction variables to be tuned simultaneously through response surface methodology. The optimized conditions were identified as a pH of 5.5, a temperature of 45.45 degrees Celsius, an incubation time of 24 hours, and an enzyme dose of 20 international units per 200 milligrams of xylan. This moderate pH and near-physiological temperature reflect the operating envelope of the enzyme itself, while the defined enzyme-to-substrate ratio ensures efficient catalysis without excessive enzyme loading, an important consideration for process economics.

Analytical characterization of the resulting hydrolysates revealed that the product was dominated by xylooligosaccharides with a degree of polymerization, or DP, ranging from 2 to 6, meaning chains of two to six xylose units. Within this range, the hydrolysate contained primarily xylohexaose, the six-unit oligomer. The DP profile is scientifically significant because oligosaccharide length governs both fermentability by gut microbes and physiological persistence. Very short oligomers are consumed rapidly in the proximal colon, while longer chains survive further along the gastrointestinal tract, enabling targeted activity. A profile centered on DP 2 to 6 therefore sits in a desirable middle zone, and the predominance of xylohexaose in this product suggests a slow, sustained fermentation profile.

The biological performance of the XOS was then evaluated in prebiotic assays using Lactobacillus salivarius, a probiotic bacterium associated with oral and intestinal health. The sorghum-derived XOS achieved a prebiotic index of 1.74, plus or minus 0.04, outperforming both commercial galacto-oligosaccharides, which scored 1.12 plus or minus 0.03, and inulin, a widely used fructan prebiotic, which scored 1.27 plus or minus 0.08. The team also reported a prebiotic activity score of 13.42 plus or minus 0.27, the highest recorded under the experimental conditions evaluated. These metrics quantify how selectively an oligosaccharide promotes the growth of beneficial bacteria relative to undesirable ones, and the magnitude of the advantage over established commercial products is one of the most notable findings of the study.

Beyond its prebiotic behavior, the XOS demonstrated a clear concentration-dependent antioxidant capacity measured by DPPH radical scavenging, a standard assay in which the degree to which a compound neutralizes a stable free radical indicates its antioxidant potential. Scavenging capacity rose gradually from 23.02 percent at 0.125 milligrams per milliliter to 75.83 percent at 4 milligrams per milliliter. This dual functionality, combining prebiotic and antioxidant properties within a single molecule, positions the sorghum-derived product as a candidate for functional food applications in which oxidative stress management and gut microbiome support are both desired outcomes.

Perhaps equally important for any ingredient intended for human consumption, the XOS displayed high resistance to simulated gastric conditions across the pH range of 1 to 5, with less than 6 percent hydrolysis after six hours of exposure. This finding addresses one of the central challenges in prebiotic delivery: the harsh acidic environment of the stomach and the enzymatic activity of the upper digestive tract can degrade many bioactive compounds before they reach the colon, where they are needed. The structural stability of these xylooligosaccharides means that the overwhelming majority of the ingested dose would arrive intact at the site of fermentation, maximizing their physiological effect.

The study was supported by the Global Centre of Excellence on Millets at ICAR-Indian Institute of Millets Research in Hyderabad, reflecting India’s broader investment in millet and sorghum-based value chains as part of national efforts to promote these climate-resilient crops. The research aligns with a growing body of literature on biomass valorization, including earlier work on enzymatic XOS production from sorghum bagasse and integrated chemo-enzymatic strategies applied to sunflower stalks and bamboo. What distinguishes the present study is the combination of high xylan recovery, rigorous statistical process optimization, and comprehensive biological characterization within a single workflow applied to a feedstock that is currently underutilized.

From a biorefinery perspective, the findings suggest a model in which sorghum stalk residue is not merely burned or returned to soil as a low-value amendment but instead becomes the basis for a high-margin nutraceutical product. Because the process relies on alkaline extraction and enzymatic hydrolysis rather than aggressive acid treatment or high-temperature thermochemical conversion, it generates a cleaner product stream with fewer degradation byproducts, simplifying downstream purification. The enzymatic step in particular offers specificity that chemical hydrolysis cannot match, producing a controlled oligosaccharide profile rather than a heterogeneous mixture.

The economic and environmental implications extend beyond sorghum itself. The principles demonstrated here, namely alkaline xylan extraction followed by optimized enzymatic conversion, are broadly applicable to other xylan-rich agricultural residues, including corn stover, wheat straw, and rice husks. As demand grows for plant-derived prebiotics to support the expanding probiotics and functional foods market, processes of this kind could allow agricultural economies to capture more value domestically from residues they already produce in abundance. India, as one of the world’s largest sorghum producers, stands to benefit considerably from translating these laboratory-scale results into industrial practice.

For now, the study establishes a rigorous technical foundation: an optimized extraction and hydrolysis protocol, a clearly defined product profile dominated by xylohexaose, and compelling evidence of prebiotic superiority over commercial benchmarks. Whether the process can be scaled economically, and whether the in vitro findings translate into health benefits in clinical settings, will be the questions that determine how far this sorghum-derived prebiotic travels from the laboratory bench to the grocery shelf. The researchers indicate that the open-access publication is intended to accelerate exactly that process, providing the detailed process parameters and analytical data that other groups will need to replicate, refine, and commercialize the approach.