The scale of the resource is staggering. National estimates place annual crop and processing residues at more than 60 million tonnes, with rice straw alone contributing roughly 40 to 50 million tonnes each year, followed by rice husk at 8 to 10 million tonnes and sugarcane bagasse at 6 to 10 million tonnes. Bamboo processing generates a further 0.75 to 1.25 million tonnes of waste, a consequence of the fact that only 50 to 70 percent of each culm finds a use, while the country’s position as the world’s second-largest coffee producer yields 0.5 to 1 million tonnes of coffee husk and pulp annually. Crucially, these volumes are not a fleeting surplus. Successive national surveys indicate that residue generation is stable or rising in step with agricultural output, meaning the feedstock base is durable rather than transient.

What makes these residues chemically attractive is their composition. Structural carbohydrates, the cellulose and hemicellulose that form the scaffolding of plant cell walls, typically account for 50 to 80 percent of the dry mass in rice straw, husk, bagasse and bamboo, and even coffee by-products contain around 45 percent. In principle, this represents a dense reservoir of fermentable sugars locked inside a recalcitrant lignocellulosic matrix. In practice, exploitation remains rudimentary: only about half of the rice husk is valorized, largely as cooking fuel or kiln feedstock, most rice straw is still burned in the fields, and modern biomass power capacity remains limited to a few sugar-mill cogeneration units and pilot husk-fired plants totalling well under 200 megawatts.

Converting those carbohydrates into useful molecules rests on two biotechnological pillars: enzymatic hydrolysis and microbial fermentation. Hydrolysis uses cellulolytic and hemicellulolytic enzymes to cleave structural polysaccharides into glucose and xylose under mild conditions, typically 45 to 50 degrees Celsius at a pH between 4.8 and 5.2. This selectivity is precisely why enzymatic routes are preferred over harsh acid hydrolysis: they consume less energy, produce fewer inhibitory by-products and preserve the sugar stream for fermentation. Performance, however, hinges on pretreatment, because lignin shields cellulose and adsorbs enzymes unproductively, while rice husk adds the complication of a silica layer. Combined alkali and hydrogen-peroxide-acetic-acid pretreatment of rice husk enabled hydrolysis yields of up to 86.3 percent at optimized enzyme loading, and for bamboo the same strategy delivered 84.3 percent of theoretical sugar yield. Remarkably, low-lignin fruit and vegetable waste needed no pretreatment at all, reaching 91 percent sugar conversion within 24 hours.

Once the sugars are liberated, microbes take over. The review catalogues an impressive array of conversions: co-fermentation of glucose and xylose with engineered Saccharomyces cerevisiae and Scheffersomyces stipitis has reached ethanol yields up to 88 percent from rice husk, bamboo and fruit waste. Succinic acid, a platform chemical for bioplastics, has been produced from rice straw and bagasse at yields of 0.18 and 0.25 grams per gram of substrate respectively, while an engineered Corynebacterium glutamicum strain converted bamboo hydrolysate to succinic acid at 63.2 percent of theoretical yield. Lactic acid, the precursor to polylactic acid bioplastic, has been obtained from mixed agricultural waste at over 80 percent conversion, and engineered Candida tropicalis has pushed xylitol production above 97 grams per litre from xylose-rich hydrolysate. Even rare sugars are on the menu: d-psicose, a low-calorie sweetener also known as d-allulose, was synthesized from rice-husk hydrolysate using xylose isomerase and d-psicose 3-epimerase at conversions of 30 to 59 percent.

The decisive insight, the authors argue, is that no single product pays the bills. First- and second-generation ethanol differ sharply in cost: the biomass-conversion step alone for lignocellulosic ethanol runs at roughly US$0.9 per gallon, more than double the US$0.3 to 0.4 per gallon for first-generation feedstocks, thanks to extra pretreatment, high enzyme loadings and lower conversion efficiencies. Two levers close this gap. The first is process integration: switching from separate hydrolysis and fermentation to simultaneous saccharification and fermentation cuts the estimated production cost from about US$2.28 to roughly US$1.48 per gallon, an approximately 35 percent reduction, by reducing reactor count, residence time and end-product inhibition. The second is co-production of higher-value chemicals that spread capital and feedstock costs across several revenue streams. Xylitol, for instance, occupies about 12 percent of the global polyol market at roughly US$4.5 to 5.5 per kilogram in bulk, an order of magnitude above ethanol, and rare sugars and prebiotic oligosaccharides command still higher food- and pharma-grade prices.

Worked examples show what such integration looks like in practice. A single rice-husk hydrolysate yielded bioethanol at 85.4 percent of theoretical yield, lactic acid at 92.5 percent and d-psicose at 40.6 percent simultaneously. Spent coffee grounds, rich in mannan, were converted by sequential alkali-bleaching pretreatment and mannanase-assisted hydrolysis into d-mannose and manno-oligosaccharides; a mass balance indicated that one kilogram of grounds yields about 40 grams of ethanol while retaining roughly 76 grams of mannose, achieved through a selective fermentation trick in which an evolved yeast mutant consumed glucose while leaving 79.9 percent of the mannose intact for recovery. Bamboo biorefining co-produced xylo-oligosaccharides at 83.9 percent xylan conversion alongside succinic and lactic acids, and in some configurations even lignin-containing cellulose nanofiber films. Across the studies, integrated cascades consistently deliver hydrolysis yields of 84 to 91 percent, ethanol yields of 85 to 88 percent, organic-acid yields of 63 to 92 percent and oligosaccharide conversions of 50 to 84 percent.

Neither technology is without its bottlenecks. Commercial cellulolytic enzymes remain expensive, a constraint that bites particularly hard in Vietnam, where enzymes are largely imported. Hydrolysis is slow relative to chemical routes, lignin adsorbs enzymes non-productively, and pretreatment can generate furan and phenolic inhibitors that poison fermentations. Fermentation itself faces incomplete pentose utilization, sensitivity to inhibitors and contamination risk in large non-sterile vessels. On the standard technology-readiness scale, the review assigns enzymatic hydrolysis and microbial fermentation levels of 5 to 7, spanning laboratory validation to pilot demonstration, while integrated biorefineries sit lower at 4 to 6, the most promising route for Vietnam yet the least demonstrated commercially. Mitigation strategies are emerging: on-site enzyme production on low-cost biomass, enzyme recycling by ultra- and nanofiltration, engineered cocktails balancing cellulase and xylanase, and robust C5-fermenting strains, which are especially relevant given that Vietnam’s dominant residues are pentose-rich.

The environmental case is equally nuanced. Diverting residues from open burning avoids particulate and greenhouse-gas emissions in a sector responsible for roughly 7 percent of global anthropogenic greenhouse-gas emissions, and the mild conditions of enzymatic and microbial processing consume less energy than thermochemical alternatives. But the authors caution that net performance is pathway-specific, depending on pretreatment chemicals, enzyme manufacture, water demand and wastewater treatment, so that energy- or solvent-intensive pretreatment can erode the savings from avoided burning. Rigorous life-cycle assessment following ISO 14040/14044, benchmarked against both open burning and the displaced fossil product, remains a critical data gap.

Perhaps the most sobering comparison is regional. Thailand has scaled bioethanol and biogas from cassava and palm residues under blending mandates and feed-in support, while Malaysia has leveraged its concentrated palm-oil waste stream toward integrated biorefineries under national biomass strategies. Vietnam, by contrast, has feed-in tariffs of about 7.03 US cents per kilowatt-hour for cogeneration and 8.47 US cents for other biomass projects, figures that lag behind solar and wind, and no dedicated instruments promoting biochemicals and biomaterials. The review concludes that the gap is institutional and structural rather than geographic, and that closing it requires organized year-round supply chains, investment in industrial-scale pretreatment and domestic enzyme production, an innovation ecosystem linking universities with industry, and policies such as tax credits and offtake guarantees that reward multi-product biorefineries rather than combustion alone. If those levers are pulled, the smoke over Vietnam’s rice fields could give way to something far more valuable.

Subject of Research: Bioconversion of Vietnam's agricultural biomass waste into high-value chemicals

Article Title: Abundant biomass waste and its potential bioconversion into high-value chemicals in Vietnam

Article References: Dien, N. T., Phuong, N. N. M., & Nguyen, T. (2026). Abundant biomass waste and its potential bioconversion into high-value chemicals in Vietnam. Case Studies in Chemical and Environmental Engineering, 14, Article 101503. https://doi.org/10.1016/j.cscee.2026.101503

Image Credits: AI Generated

DOI: 10.1016/j.cscee.2026.101503

Keywords: biomass waste, Vietnam, bioconversion, biorefinery, enzymatic hydrolysis, microbial fermentation, bioethanol, lactic acid, xylitol, rare sugars, rice straw, circular bioeconomy

The study, published in the Journal of Medical and Biological Engineering, focused on the three elements that define healthy enamel chemistry: calcium, phosphorus, and oxygen. Enamel is composed almost entirely of hydroxyapatite, a crystalline mineral built from calcium and phosphate ions arranged in a tight lattice, with oxygen bound within the phosphate groups. When acids dissolve this lattice, calcium and phosphorus leach out of the crystal structure in a process called demineralization, leaving behind a weakened, porous surface that bacteria can penetrate. Reversing that loss — restoring calcium and phosphorus while managing the oxygen signature of the surface — is the central goal of remineralization therapy.

To test whether their dual approach could accomplish this, Ghada A. Ibrahim of Osol AL-ELM University College and Al-Baladiyat Specialized Dental Centre, together with Eaman A. Al-Rubaee of the University of Baghdad, Maha J. Abbas of Mustansiriyah University, and Nisreen Kh. Abdalameer of the University of Baghdad, collected fifty human maxillary first premolars. The teeth were divided into five groups of ten: four experimental groups and one control. On each tooth, the researchers prepared a round window on the buccal, or cheek-facing, surface to serve as a standardized test site. They then induced artificial caries-like lesions using a pH cycling method, a laboratory technique that alternates the teeth between acidic and neutral environments to mimic the repeated acid attacks that occur in the mouth.

The experimental treatments were deliberately simple in concept but sophisticated in execution. One group received PLGA/xylitol nanoparticles at a concentration of 5 percent. PLGA, short for poly(lactic-co-glycolic acid), is a biodegradable polymer widely used in medicine to deliver drugs safely into tissues; embedding xylitol — a sugar alcohol known to interfere with the metabolism of cavity-causing Streptococcus mutans — inside these nanoparticles allows the compound to penetrate deep into bacterial biofilms and linger on the enamel surface. Other groups received cold atmospheric plasma, a partially ionized gas that operates near room temperature and generates a cocktail of reactive oxygen and nitrogen species, charged particles, and ultraviolet photons capable of killing bacteria without damaging surrounding tissue. Two groups combined the two therapies, applying them in different sequences: nanoparticles followed by plasma, or plasma followed by nanoparticles.

The researchers tracked the elemental composition of the enamel at three stages — sound, demineralized, and treated — using energy dispersive spectroscopy, or EDS. This analytical technique, typically paired with a scanning electron microscope, bombards the sample with an electron beam and reads the characteristic X-rays emitted by each element, allowing precise quantification of the surface chemistry without destroying the specimen. The results revealed a clear pattern. After treatment, every experimental group showed an increase in calcium except the plasma-only group and the control group, and every experimental group showed an increase in phosphorus except the control. Oxygen, by contrast, decreased after treatment in all groups except the PLGA/xylitol nanoparticle group — a shift the researchers interpret as evidence of mineral redeposition, since newly formed hydroxyapatite incorporates oxygen into its phosphate lattice while displacing surface oxygen associated with demineralized, oxidized tissue.

The most striking numbers came from the combined-therapy groups. EDS analysis showed that the greatest difference in mean calcium and phosphorus values between the demineralization and remineralization stages occurred in the group that received nanoparticles first and plasma second, followed closely by the group treated with plasma before nanoparticles, with statistically significant differences. The plasma-plus-nanoparticles group achieved the highest calcium and phosphorus readings of all, at 34.520 ± 6.382 and 14.860 ± 0.757 respectively, while the nanoparticles-plus-plasma group followed at 33.420 ± 1.878 and 14.560 ± 0.704. These values approach the composition of sound enamel, suggesting that the combined treatment did not merely halt demineralization but actively drove the surface back toward its original mineral density.

The researchers conclude that the enamel surface treated with cold atmospheric plasma and PLGA/xylitol nanoparticles produced favourable results in increasing the microhardness of the tooth through its chemical elements, implying that this therapy might be recommended as a method of preventing dental cavities. Microhardness — the resistance of the enamel surface to localized indentation — is a well-established proxy for mineral content, and its recovery alongside calcium and phosphorus restoration indicates that the treated enamel regained genuine structural integrity rather than a superficial coating.

The mechanisms behind the synergy are plausible and physically grounded. Cold plasma is known to alter the surface energy and wettability of enamel, creating reactive sites that can bind mineral ions more readily; previous studies have shown that plasma pretreatment increases fluoride uptake from varnishes and modifies enamel and dentin surfaces in ways that favour remineralization. Meanwhile, the PLGA carrier degrades slowly into lactic acid and glycolic acid — metabolites the body already processes — releasing xylitol gradually at the tooth surface while its nanoscale dimensions allow penetration into the extracellular polymeric substances of bacterial biofilms, disrupting the communities that produce the very acids causing demineralization. Applied in sequence, the plasma may prime the enamel surface for mineral binding while the nanoparticles suppress the bacterial acid production that would otherwise undo the gains.

The study carries important caveats. It was conducted entirely in vitro, on extracted teeth in a laboratory setting, where the complex environment of the human mouth — saliva, dietary variation, plaque dynamics, and individual differences in oral hygiene — is absent. The sample size of ten teeth per group is modest, and the pH cycling model, while widely accepted, cannot fully replicate the years-long progression of natural caries. Ethical approval was granted by the Ethical Committee of the College of Dentistry at the University of Baghdad in accordance with the Helsinki Declaration, and the authors affirm no conflicts of interest, but clinical translation will require in vivo studies and, ultimately, randomized controlled trials before dentists can reach for a plasma jet and a vial of nanoparticles in everyday practice.

Nevertheless, the findings add to a growing body of evidence that the future of dentistry may lie less in repairing damage and more in preventing it at the molecular scale. Nanohydroxyapatite pastes, bioactive glasses, and antimicrobial nanoparticles are already being explored as remineralization agents, and cold plasma has demonstrated antibacterial effects against the microorganisms responsible for dental caries in earlier work by some of the same research groups. By quantifying exactly how calcium, phosphorus, and oxygen shift across the demineralization-remineralization boundary under combined nanoparticle and plasma treatment, this study provides a chemical fingerprint that future therapies can be measured against. If subsequent research confirms these results in living teeth, the humble filling — the defining symbol of dental care for over a century — may one day share the clinic with a technology that stops cavities before they begin.

Subject of Research: The Impact of PLGA/ Xylitol Nanoparticles and Cold Atmospheric Plasma on the Chemical Element(Calcium (Ca), Phosphorus (P), Oxygen (O)) of the Dental Enamel (in Vitro Study)

Article Title: The Impact of PLGA/ Xylitol Nanoparticles and Cold Atmospheric Plasma on the Chemical Element(Calcium (Ca), Phosphorus (P), Oxygen (O)) of the Dental Enamel (in Vitro Study)

Article References: Ibrahim, G. A., Al-Rubaee, E. A., Abbas, M. J., & Abdalameer, N. K. (2026). The Impact of PLGA/ Xylitol Nanoparticles and Cold Atmospheric Plasma on the Chemical Element(Calcium (Ca), Phosphorus (P), Oxygen (O)) of the Dental Enamel (in Vitro Study). Journal of Medical and Biological Engineering. https://doi.org/10.1007/s40846-026-01057-3

Image Credits: AI Generated

DOI: 10.1007/s40846-026-01057-3

Keywords: Impact, PLGA, Xylitol, Nanoparticles, Cold, Atmospheric, Plasma, Chemical, Element, Calcium, Phosphorus, Oxygen

The review, authored by Yuefan Zhang, Yan Zhang, Shuo Xia, Aamer Ali Shah, Rui Zhang and corresponding author Chunjie Gong of Hubei University of Technology and collaborating institutions, arrives at a moment when demand for xylitol is climbing alongside the global rise in diabetes. Unlike sucrose, xylitol delivers sweetness with a low glycemic impact, and decades of research have linked it to benefits ranging from cavity prevention to possible roles in respiratory health, skin barrier function and gut microbiome modulation. But producing it at industrial scale remains expensive, and the new analysis argues that the answer lies not in better chemistry but in smarter biology.

At the heart of the biological route is a single enzymatic step. Xylose, a five-carbon sugar abundant in hemicellulose from agricultural waste such as corncobs, sugarcane bagasse, wheat straw and rice straw, is reduced to xylitol by the enzyme xylose reductase. In nature, yeasts such as Candida tropicalis, Candida guilliermondii, Debaryomyces hansenii and Yarrowia lipolytica perform this conversion, and bacteria including Enterobacter species and engineered Escherichia coli can be coaxed to do the same. The catch is that the reaction consumes reduced nicotinamide cofactors, NADH or NADPH, which the cell must continuously regenerate. When cofactor supply runs dry, production stalls, and unwanted byproducts accumulate as the microbe reroutes carbon elsewhere.

This cofactor bottleneck is precisely where modern metabolic engineering has made its mark. The review details how researchers have rebuilt xylitol pathways from the ground up: overexpressing xylose reductase, deleting xylitol dehydrogenase so the product cannot be consumed again, and rewiring the pentose phosphate pathway to pump out the NADPH the reductase demands. In engineered E. coli, teams have multiplied copies of the xylose reductase gene while deleting genes of the Embden-Meyerhof-Parnas glycolytic route, forcing carbon flux toward NADPH regeneration and sharply improving yields. Similar logic has been applied in yeasts, where co-expression of pentose phosphate pathway genes in Candida tropicalis boosted xylitol titers, and disruption of the xylitol dehydrogenase gene under fully aerobic conditions raised both productivity and yield.

Beyond single-gene interventions, the field has embraced modular design. Rather than tweaking one enzyme at a time, synthetic biologists now assemble pathway modules that can be independently tuned, balancing expression strengths through choices of promoters and ribosome binding sites. Dynamic control systems add another layer of sophistication: in engineered E. coli, researchers have placed feedback regulatory loops under programmable control, improving NADPH flux and xylitol biosynthesis simultaneously. Cofactor engineering has even extended to redesigning the coenzyme specificity of central metabolic enzymes, a strategy proven in other products and increasingly relevant to xylitol, where the balance between NADH and NADPH dictates how much reducing power is available for the key reductive step.

Choice of host organism matters as much as pathway design. The review weighs the trade-offs among industrial chassis cells: natural xylose-fermenting yeasts like Candida and Debaryomyces species are robust on lignocellulosic hydrolysates but may not be food-grade; the baker’s yeast Saccharomyces cerevisiae is Generally Recognized As Safe and genetically tractable but needs extensive engineering to consume xylose efficiently; E. coli grows fast and tolerates manipulation but raises regulatory hurdles for food applications. Thermotolerant hosts such as Kluyveromyces marxianus offer the bonus of high-temperature fermentation, cutting cooling costs, while oleaginous yeasts like Yarrowia lipolytica can co-consume crude glycerol and xylose, turning two waste streams into one product. Even filamentous fungi have entered the arena, with engineered Neurospora crassa producing xylitol from xylose and Aspergillus niger converting L-arabinose into the sweetener.

Feedstock strategy is evolving in parallel. Hemicellulosic hydrolysates from corncob, sugarcane bagasse, wheat straw, rapeseed straw and even banana peel provide cheap xylose, but they carry inhibitors, furans and acids, that poison fermentation, requiring detoxification steps. Recent work has explored co-substrate models that pair xylose with other sugars to sustain cofactor regeneration, and a striking new mode uses the microalga Chlorella sorokiniana driven synergistically by light and co-substrates to biosynthesize xylitol, hinting at photosynthesis-assisted production. Adaptive laboratory evolution, in which strains are bred for tolerance to hydrolysate toxins over many generations, rounds out the toolkit for making industrial feedstocks usable.

The most forward-looking section of the review concerns artificial intelligence. Machine learning models, from artificial neural networks and support vector regression to deep neural networks, are already predicting fermentation outcomes and optimizing bioreactor parameters, with early demonstrations coupling neural networks to genetic algorithms to maximize xylitol production by Debaryomyces nepalensis. Protein language models and structure-prediction systems of the AlphaFold era now allow researchers to forecast enzyme properties and steer directed evolution of xylose reductases toward higher activity and better cofactor preference, while deep learning tools navigate biosynthetic pathways for natural products. Genome-scale metabolic models fused with machine learning can characterize cell growth from multi-omics data, and multimodal networks promise to integrate fermentation time-courses with transcriptomic and flux information into unified predictive frameworks.

All of this feeds into what the authors describe as a closed-loop design-build-test-learn cycle. In this framework, AI predicts metabolic network behavior and proposes enzyme variants; automated construction builds the strains; high-throughput testing measures performance; and the results are fed back to refine the models. Computational fluid dynamics and process modeling extend the loop from the cell to the bioreactor, while techno-economic and sustainability analyses, including assessments of xylitol production within integrated biorefinery platforms aimed at circular economies, evaluate whether bio-xylitol can compete with petrochemical and catalytic hydrogenation routes on cost and carbon footprint.

The review is candid about remaining obstacles: enzymatic bottlenecks, carbon flux imbalances, feedstock variability, downstream purification costs and the regulatory demands of food-grade production all persist. It also notes that the health conversation around xylitol is not settled, with recent research reporting potential prothrombotic associations that warrant attention even as dental and metabolic benefits remain well documented. Still, the authors conclude that the convergence of rational metabolic engineering, food-grade chassis optimization and AI-guided bioprocessing provides a comprehensive blueprint for making microbial xylitol economically viable. If the design-build-test-learn loop matures as its proponents hope, the sweetener in sugar-free gum and diabetic-friendly foods may soon come from fermentation tanks where algorithms, not just chemists, decide what the microbes make next.

Subject of Research: Metabolic engineering and AI-driven bioprocessing of microbial cell factories for xylitol production

Article Title: Advances in microbial cell factories for substitute sugar xylitol production: from metabolic engineering to AI-driven bioprocessing

Article References: Zhang, Y., Zhang, Y., Xia, S., Shah, A. A., Zhang, R., & Gong, C. (2026). Advances in microbial cell factories for substitute sugar xylitol production: from metabolic engineering to AI-driven bioprocessing. 3 Biotech, 16(10), Article 427. https://doi.org/10.1007/s13205-026-05072-8

Image Credits: AI Generated

DOI: 10.1007/s13205-026-05072-8

Keywords: xylitol, metabolic engineering, microbial cell factories, xylose reductase, cofactor engineering, synthetic biology, artificial intelligence, bioprocessing, lignocellulosic biomass, sugar substitute, pentose phosphate pathway, industrial biotechnology