The motivation is both environmental and economic. In Canada, heat production, electricity generation, and transportation fuels account for roughly 73 percent of greenhouse gas emissions, and the country has pledged to cut total emissions by 40 to 45 percent by 2030 and reach net zero by 2050. Saskatchewan, one of the provinces most dependent on coal-fired electricity, is also the nation’s agricultural powerhouse: more than 40 percent of Canada’s total cropland lies within its borders, and the country produces an estimated 82.4 million metric tons of agricultural residues each year. Converting even a fraction of that stream into clean-burning fuel would simultaneously reduce waste disposal problems, curb open burning of stubble, and displace fossil fuels in power plants.

Raw agricultural residues, however, make poor fuels on their own. They are bulky, hygroscopic, oxygen-rich, and energy-dilute, with heating values in the study’s raw samples ranging only from 17.6 to 18.5 megajoules per kilogram. Their high moisture content saps combustion efficiency, and their tendency to absorb water makes long-term storage a nightmare of mold and decay. Torrefaction addresses these weaknesses directly. The process heats biomass to between 200 and 350 degrees Celsius for anywhere from half an hour to two hours, driving off moisture and volatile compounds and leaving behind a darker, drier, carbon-enriched solid sometimes called bio-coal. In this study, the team used oxidative torrefaction—running the reaction in air rather than an inert nitrogen atmosphere—a choice that dramatically lowers cost and complexity at industrial scale.

The researchers torrefied all four feedstocks at 250, 275, and 300 degrees Celsius for 60 minutes in sealed stainless-steel reactors. The transformation was striking. Elemental carbon content, which started between 44.6 and 46.9 weight percent across the raw materials, climbed to between 65.2 and 69.8 weight percent after treatment at 300 degrees Celsius. Meanwhile, oxygen and hydrogen were stripped away through dehydration, depolymerization, and decarboxylation reactions that release water, acetic acid, carbon monoxide, carbon dioxide, and light hydrocarbons. On a Van Krevelen diagram, which plots atomic hydrogen-to-carbon against oxygen-to-carbon ratios, the torrefied samples marched steadily toward the coal corner of the chart. After treatment at 300 degrees Celsius, the oxygen-to-carbon ratio fell by more than 71 percent for every feedstock, and the hydrogen-to-carbon ratio dropped by roughly half.

The heating values told an equally compelling story. Torrefaction at 250 degrees Celsius already pushed the fuels into the 23.8 to 25.4 megajoule per kilogram range, and the most severe treatment lifted hemp straw to 29.0 megajoules per kilogram—the highest value in the study. That figure places torrefied hemp straw squarely in the territory of sub-bituminous coals, meaning it could potentially be co-fired in existing coal infrastructure with minimal modification. Moisture content, meanwhile, plummeted by 35.7 to 82.4 percent depending on the feedstock, because the heat destroys the hydroxyl groups that normally form hydrogen bonds with water. The result is a hydrophobic fuel that resists reabsorbing moisture during storage, grinds more easily, and burns with less smoke and water vapor, losing less energy up the stack.

To provide a rigorous comparison, the team also ran all four residues through steam explosion at the Canadian Feed Research Centre in Saskatoon. In that process, biomass is exposed to pressurized steam at roughly 300 pounds per square inch for one minute and then subjected to explosive decompression that physically ruptures the rigid fiber structure. Steam explosion did deliver some benefits: it altered lignin structure, increased cellulose crystallinity, and improved the material’s suitability for pelletization. But its chemical impact proved modest. Heating values rose only slightly, from 17.6 to 18.5 megajoules per kilogram in raw samples to between 18.2 and 19.6 megajoules per kilogram after treatment, and elemental composition barely shifted. The contrast illuminates the fundamental difference between the two technologies: steam explosion is primarily a physical restructuring of the biomass, while torrefaction is an irreversible chemical conversion that fundamentally rewrites the fuel’s composition.

Spectroscopic analysis confirmed the chemistry. Fourier transform infrared spectra of torrefied samples showed weakened peaks associated with cellulose and hemicellulose, indicating decomposition of those polymers, and a flattened hydroxyl stretching band consistent with moisture loss. A new peak emerged in the aromatic carbon-hydrogen bending region, signaling that lignin-derived aromatic rings had recombined and formed during heating. The steam-exploded samples, by contrast, looked nearly identical to their raw counterparts in the spectra. Compositional analysis of the raw materials showed the four residues shared similar architectures—hemicellulose contents of 26 to 35 percent and comparable cellulose levels in three of the four—which suggests the findings could generalize across a wide swath of prairie biomass.

The study also confronted an awkward truth about biomass combustion: ash. X-ray fluorescence analysis revealed that potassium and sodium, the alkali metals responsible for fouling boiler heat-exchange surfaces and agglomerating fluidized beds, were abundant in most samples. Predictive indices showed that nearly all torrefied fuels carried a high probability of fouling and slagging, with raw wheat straw scoring an alkali index of 1.93 kilograms per gigajoule—well above the 0.34 threshold at which fouling becomes almost certain. The researchers note that water or acid leaching before torrefaction could strip out these troublesome alkalis, and that adjusting or doping the bed material in fluidized-bed combustors offers another mitigation route. Hemp straw emerged as the cleanest candidate, with the lowest potassium content and a low fouling probability even after treatment.

The economics of scaling up shaped the final analysis. Solid yields declined as torrefaction temperature rose, since devolatilization sacrifices mass to concentrate energy—hemp straw lost 14.6 weight percent of yield moving from 250 to 275 degrees Celsius. Energy yields at 250 degrees Celsius clustered between 62.6 and 64.9 percent but fell as temperatures climbed, creating a classic trade-off between fuel quality and fuel quantity. To find the sweet spot, the team calculated an energy-mass co-benefit index, which peaked at 275 degrees Celsius for canola straw, hemp straw, and wheat straw, and at 300 degrees Celsius for oat hulls. That optimization framework, the authors argue, gives industry a practical target rather than a simple push toward maximum severity.

Challenges remain before torrefied prairie straw feeds a power plant. Torrefied biomass is harder to pelletize than raw material, requiring binders that add cost, and industrial-scale reactors still struggle with uniform heat distribution and process control. Large-scale life-cycle assessments, product standardization, and supportive policy all lag behind the science. Yet the study’s verdict is clear: oxidative torrefaction transforms abundant, cheap agricultural waste into a hydrophobic, coal-like fuel with heating values up to 29 megajoules per kilogram, outperforming steam explosion on every major fuel metric. For a province sitting on tens of millions of tons of residue while burning coal for electricity, the path from field waste to clean power may run through a furnace set at 275 degrees Celsius.

Subject of Research: Upgrading agricultural residues into solid biofuels through oxidative torrefaction and steam explosion pretreatment

Article Title: Development of biofuels from agricultural residues via torrefaction and steam explosion

Article References: Wattan, R., Zamiri, M. A., Newkirk, R., Dalai, A. K., & Acharya, B. (2026). Development of biofuels from agricultural residues via torrefaction and steam explosion. Results in Engineering, 32, Article 113252. https://doi.org/10.1016/j.rineng.2026.113252

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113252

Keywords: torrefaction, steam explosion, biofuels, agricultural residues, lignocellulosic biomass, higher heating value, canola straw, hemp straw, wheat straw, oat hulls, fouling and slagging, renewable energy

A research team led by Tingchen Si and colleagues, publishing in Food Chemistry: X, has now systematically tested two contrasting pretreatment strategies to solve this dilemma: steam explosion and heat curing. Their goal was ambitious. Rather than simply stabilizing the mushroom powder, they wanted to know whether these treatments could actively upgrade it, enhancing flavor, refining particle structure, and improving compatibility with wheat dough so that the powder could be folded into noodles without wrecking the gluten network. The work combined electronic nose profiling, gas chromatography-ion mobility spectrometry, free amino acid quantification, infrared spectroscopy, particle size analysis, electron microscopy, and a battery of dough rheology tests, offering one of the most complete pictures yet of how processing reshapes a functional mushroom ingredient.

Steam explosion is a dramatic technique by any standard. Dried mushroom pieces were rehydrated for twelve hours, then loaded into a pressurized chamber where saturated steam at 0.6, 0.9, or 1.2 megapascals was held for five minutes before an abrupt release of pressure. In that instant, stored thermal energy converts into mechanical energy, tearing apart cell walls and fibrous architecture. Heat curing took a gentler path: ground mushroom powder spread in thin layers was heated at 90, 100, 110, or 120 degrees Celsius for fifteen minutes each. The two methods thus represent opposite philosophies, one delivering a violent mechanical shock in seconds, the other applying controlled, sustained heat.

The amino acid results were striking. Steam explosion at 0.9 megapascals more than doubled total free amino acids, raising them from 26.54 milligrams per gram in untreated powder to 66.89 milligrams per gram. Umami amino acids such as glutamic and aspartic acid, the molecular backbone of savory taste, nearly doubled, while sweet amino acids climbed almost threefold. The mechanism is physical as much as chemical: the pressure release disrupts intracellular matrices and releases pre-existing free amino acids, while high-temperature, high-pressure conditions denature proteins, unfold peptide chains, and weaken non-covalent interactions, making proteins vulnerable to degradation into smaller nitrogenous compounds. Crucially, the short residence time limits the Maillard reaction, so amino acids are liberated faster than they are consumed. Pressure mattered enormously. At 0.6 megapascals the disruption was insufficient; at 1.2 megapascals excessive thermal exposure drove secondary degradation, reducing net accumulation. The 0.9 megapascal condition hit the sweet spot.

Heat curing told a different story. At 90 degrees Celsius, total free amino acids rose modestly to 29.92 milligrams per gram, but every additional ten degrees pushed them sharply downward, falling to just 13.02 milligrams per gram at 120 degrees. The culprit is the Maillard reaction, which accelerates at higher temperatures as amino acids react with reducing sugars to form melanoidins and heterocyclic compounds, consuming precisely the umami amino acids that give mushrooms their appeal. Prolonged high heat can also trigger deamidation and oxidative degradation of asparagine and glutamine, while cellular autolysis activates endogenous proteases that further erode the free amino acid pool. The lesson is that heat curing rewards restraint: gentle temperatures preserve, aggressive ones destroy.

Aroma analysis revealed equally distinctive fingerprints. Gas chromatography-ion mobility spectrometry detected 106 volatile organic compounds across the samples, including 17 esters, 15 aldehydes, 14 alcohols, 11 ketones, and 6 pyrazines. Untreated powder retained a natural, plant-like profile dominated by pentanal, octanal, and ethyl acetate, with fruity and green notes. Heat-cured powder developed elevated concentrations of butanal, 3-methylbutanal, and various esters, producing sweet, chocolate-like fruity aromas alongside pungent sulfides. Steam-exploded powder underwent the most dramatic transformation: high-temperature, high-pressure conditions promoted Maillard chemistry, generating roasted, nutty pyrazines such as 2-ethyl-3-methylpyrazine alongside characteristic mushroom ketones like 1-octen-3-one. Principal component analysis confirmed that the volatile profiles of the treated and untreated powders were clearly separable, with the first two components explaining 94 percent of the variance.

Structural measurements reinforced why these powders behave differently in dough. Steam-exploded powder had the smallest median particle size, at 136.96 micrometers compared with 187.99 micrometers for untreated powder, because the instantaneous pressure release shatters cell walls and fibrous networks into finer fragments. Scanning electron microscopy showed the steam-exploded particles with loosened, disrupted microstructure and smoother surfaces, while untreated and heat-cured powders displayed wrinkled, compact, rough textures. Fourier transform infrared spectroscopy, meanwhile, showed that the fundamental functional groups, including hydroxyl stretches near 3432 per centimeter and carbonyl bands near 1640 per centimeter, were broadly retained across all treatments, meaning the chemical identity of the mushroom matrix survived even as its physical architecture was rebuilt.

The decisive test came when the powders were blended into wheat flour at substitution levels of 1, 3, 5, and 7 percent. Mixolab thermomechanical analysis showed that untreated mushroom powder steadily degraded dough performance, cutting stability time from 7.95 minutes to 3.60 minutes at 7 percent substitution as the dilution of gluten-forming proteins weakened the cohesive network. Steam-exploded powder behaved remarkably differently: stability time barely changed, holding at 7.35 minutes even at 7 percent substitution, apparently because the modified fiber and polysaccharide components disperse well within the gluten-starch matrix and interact constructively with gluten proteins. Water absorption rose in all formulations, reflecting the mushroom powder’s strong water-holding capacity, but the processed powders demanded less added water than the untreated one. The 5 percent substitution level emerged as the optimal balance, enhancing functional contribution while preserving gluten network integrity.

Rheological and pasting measurements added further nuance. All composite doughs exhibited elastic-dominant viscoelastic behavior, with storage modulus exceeding loss modulus across the tested frequency range and loss tangent values below one, indicating solid-like structures suitable for noodle processing. Rapid Visco Analyzer results showed that peak viscosity declined with mushroom addition, most sharply for heat-cured powder, whose water-hungry fiber competes with starch for moisture and restricts granule swelling. Steam-exploded powder, by contrast, released soluble polysaccharides that partially compensated for this restriction, keeping peak viscosity statistically indistinguishable from the control. Setback values, which track starch retrogradation during cooling and predict staling, fell in all mushroom-supplemented samples, suggesting the treated powders could help noodles stay fresher longer.

Low-field nuclear magnetic resonance provided the final piece of the puzzle by tracking water mobility inside the dough. All samples showed three proton populations corresponding to bound, partially immobilized, and free water, but the steam-exploded and heat-cured formulations shifted the transverse relaxation times of the immobilized water fraction to longer values, indicating increased water mobility and weaker water-matrix interactions. This redistribution, likely tied to the porous microstructure of the treated fibers, can improve gluten hydration and dough softness while influencing starch retrogradation. Taken together, the findings sketch a practical decision framework for food manufacturers: steam-exploded powder at 0.9 megapascals suits flavor-focused, high-dispersibility applications such as noodles, while 90-degree heat-cured powder, with its enhanced sweet aroma compounds and preserved organic acids, fits bakery and steamed bread products where elasticity and aroma matter most. Both routes turn a perishable, flavor-fragile mushroom into a stable, functional ingredient, and both leave the gluten network largely intact at moderate substitution levels, bringing wine-cap mushroom noodles a significant step closer to the supermarket shelf.

Subject of Research: Effects of steam explosion and heat curing pretreatments on the physicochemical properties of Stropharia rugosoannulata powder and wheat dough quality

Article Title: Effects of steam explosion and heat curing on the physicochemical properties of Stropharia rugosoannulata powder and dough quality

Article References: Si, T., Arshad, A., Intizar, A., Rong, Q., Liu, S., Sun, Y., Li, X., Gao, K., & Liang, J. (2026). Effects of steam explosion and heat curing on the physicochemical properties of Stropharia rugosoannulata powder and dough quality. Food Chemistry: X, 39, Article 104502. https://doi.org/10.1016/j.fochx.2026.104502

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104502

Keywords: wine-cap mushroom, Stropharia rugosoannulata, steam explosion, heat curing, free amino acids, umami, flavor compounds, dough rheology, noodles, dietary fiber, LF-NMR, food processing

Led by Junie Albine Kenfack Atangana of the University of Yaounde 1 and the Polytechnic University of Bucharest, together with colleagues in Cameroon, Romania, and Germany, the review follows PRISMA guidelines, screening 500 unique records down to 119 high-quality studies. These comprised 42 studies of physical pretreatment, 38 of chemical methods, 29 of biological approaches, and 10 of combined strategies, alongside embedded life cycle assessments and techno-economic analyses. Unlike earlier reviews that lumped together sewage sludge, food waste, and microalgae, this analysis focuses exclusively on agricultural waste, offering quantitative comparisons that have been largely missing from the literature.

The headline numbers are striking. Physical pretreatments, including mechanical milling and steam explosion, are the most mature technologies, sitting at technology readiness levels 7 to 9, and they deliver methane yield increases of 10 to 50 percent for large-scale, low-lignin feedstocks. Steam explosion, which ruptures biomass fibers by suddenly depressurizing high-pressure steam, can raise methane yields by 30 to 100 percent for lignocellulosic residues. But the authors sound a cautionary note: physical methods are energy hungry. Microwave and ultrasonication treatments rank among the most electricity-intensive options, and when the energy consumed during grinding and disintegration is honestly included in energy balances, many studies that once looked impressive collapse into marginal gains of less than 5 percent. The review argues that this systematic omission of pretreatment energy costs is one of the most pervasive methodological flaws in the field.

Chemical pretreatments offer a different trade-off. Alkaline methods using sodium hydroxide or lime, and organosolv processes using organic solvents, can raise methane yields by 20 to 100 percent for lignin-rich biomass such as straw and wood residues. Lime in particular emerges as a cost-effective and environmentally favorable option, especially when the hydroxide solution is recirculated to avoid water-intensive washing steps. But chemical routes carry hidden liabilities: sodium from NaOH and sulfur from sulfuric acid can accumulate in the digestate, degrading its value as fertilizer, while acid hydrolysis generates well-known inhibitors such as furfural and hydroxymethylfurfural that suppress the very methanogens the process is meant to feed. The reviewers note that most techno-economic analyses assume idealized reagent prices and omit neutralization costs, making their relevance to real-world decision-making questionable.

Biological pretreatments occupy a gentler but slower niche. Fungal treatments using Trichoderma and Aspergillus species, bacterial consortia, and enzymatic cocktails deliver methane increases of 15 to 70 percent with low operating costs, no corrosive chemicals, and a positive influence on digestate quality. Fungal treatments sit at technology readiness levels 5 to 7, and ensiling, which preserves biomass while lactic acid bacteria initiate partial acid hydrolysis, reaches full commercial maturity. The drawback is time: fungal and bacterial treatments can require days to weeks, implying large reactor volumes and high capital costs. Commercial enzymes, priced at roughly 5 to 20 US dollars per kilogram, remain hard to justify for low-margin biogas operations unless produced on-site.

Where the review breaks new ground is in its analysis of combined strategies, synthesized from ten studies. Sixty percent of the combined pretreatments demonstrated genuine synergy, with an average improvement of about 12 percent beyond what the individual methods would predict. Simultaneous applications, such as microwave-alkaline coupling and thermal KOH combined with steam explosion, showed synergy in 100 percent of cases. Even more compelling are integrated biological strategies that piggyback on existing process streams. Digestate recirculation, which transfers alkalinity and active microbes back into the digester, achieves operating expenditure savings of up to 86 percent compared with conventional post-treatment. Ensiling, meanwhile, cuts greenhouse gas emissions by an estimated 250 megagrams of CO2-equivalent per 1000 hectares, though it brings trade-offs including a 38 percent increase in nitrogen leaching and long-term soil carbon losses. Co-digestion with manure supplies trace elements like nickel, iron, and cobalt that methanogens need, along with ligninolytic enzymes that help dismantle recalcitrant fibers.

Environmental performance, the reviewers stress, is profoundly context-dependent. Electricity-driven physical methods inherit the carbon intensity of the local grid, meaning the same ultrasonication unit can be climate-friendly in Norway and damaging in a coal-powered region. Steam explosion can reduce climate impacts by up to 0.134 kilograms of CO2-equivalent per kilowatt-hour when biomass displaces fossil heat, but methane leakage from digesters remains a persistent burden. Chemical pretreatments introduce salt accumulation unless lime recirculation is employed. The authors argue that no pretreatment technology can be judged in isolation from these upstream and downstream factors, and that apparent methane gains are frequently offset by hidden environmental costs elsewhere in the system.

To guide practitioners through this complexity, the review proposes a decision framework organized around five criteria: feedstock lignin content, plant scale, digestate quality requirements, economic feasibility, and strategic objectives such as co-product recovery. For lignin-rich residues like straw and nutshells, alkaline or organosolv chemical methods make the most sense. Low-lignin biomass needs only mechanical milling or steam explosion. Industrial continuous plants favor fast physical and chemical methods, while small farms and decentralized systems are best served by biological approaches, particularly ensiling and manure co-digestion, which require little more than silos and storage vessels. If digestate must serve as high-quality fertilizer, biological pretreatment is the only option that actively improves it.

Looking forward, the authors identify nanotechnology as an emerging enhancement layer rather than a replacement. Conductive nanoparticles, including zero-valent iron and nickel, graphene oxide, and carbon nanotubes, can stimulate direct interspecies electron transfer between fermentative bacteria and methane-producing archaea, accelerating the rate-limiting step of methanogenesis. Magnetic nanoparticles may also improve biomass separation and microbial retention. But at technology readiness levels 3 to 5, unresolved questions about cost, ecotoxicity, recovery, and regulation confine nanotechnology to research and pilot applications for now. The review’s broader message is that the field urgently needs region-specific, multi-feedstock studies, standardized reporting of methane rather than merely biogas yields, integrated life cycle and techno-economic assessments, and predictive models that link substrate composition to optimal treatment conditions. Pretreatment, the authors conclude, is not an optional add-on but the cornerstone of the biogas cycle, and getting it right is essential for a genuinely sustainable circular energy future.

Subject of Research: Pretreatment strategies for enhancing anaerobic digestion and biogas production from agricultural waste

Article Title: Advances challenges and future directions of pretreatment strategies for enhancing biogas production from agricultural waste

Article References: Kenfack Atangana, J. A., Tiegam Tagne, R. F., Kounou Ndongo, G., Covaliu Mierla, C. I., Ștefan Biriș, S., & Paraschiv, G. (2026). Advances challenges and future directions of pretreatment strategies for enhancing biogas production from agricultural waste. Discover Green Chemistry, 1(1), Article 22. https://doi.org/10.1007/s44509-026-00022-2

Image Credits: AI Generated

DOI: 10.1007/s44509-026-00022-2

Keywords: biogas, agricultural waste, anaerobic digestion, pretreatment, methane yield, lignocellulosic biomass, steam explosion, alkaline pretreatment, ensiling, digestate recirculation, life cycle assessment, nanotechnology