New Method Strips Yeast Glucans to Reveal True Cellulose in Fermentation Samples

Measuring cellulose sounds like it should be one of the straightforward tasks in analytical chemistry: take a sample, dissolve the interfering materials, and quantify what remains. In industrial grain fermentation, however, the reality is far messier. A fermentation intermediate drawn from a working ethanol plant is a dense slurry of partially digested grain, residual starch fragments, and enormous populations of yeast cells, all of which carry polysaccharides of their own. When analysts try to isolate and measure the small amount of cellulose that may be present in such a matrix, the signals from these other glucans can swamp or distort the result. A new study published in Biotechnology for Biofuels and Bioproducts by Justin Sluiter and Katie Michel of the National Laboratory of the Rockies, together with colleagues at Novonesis and POET, describes an analytical procedure designed to cut through that ambiguity and deliver a defensible number for cellulose content and conversion in mixed, industry-relevant samples.

The core problem the team set out to address lies in how cellulose has traditionally been separated from everything else in a sample. Conventional protocols rely on cold caustic extraction, in which a strong alkali solution is used to dissolve non-cellulosic glucans while leaving crystalline cellulose behind as a solid residue. That approach works reasonably well for clean biomass samples, but it carries a known risk: under cold caustic conditions, cellulose can undergo what chemists call mercerization, a transformation in which the crystalline structure of the polymer is altered and some of the material can be lost or converted into forms that no longer respond to the assay. For samples that contain only trace amounts of cellulose to begin with, such as grain fermentation intermediates, even a small systematic loss of this kind can translate into a large relative error, potentially masking the very conversion the process engineers are trying to detect.

To sidestep mercerization entirely, the researchers turned to dimethyl sulfoxide, or DMSO, as the solvent for removing the non-cellulosic carbohydrates. DMSO is a polar aprotic solvent with a long history in carbohydrate chemistry, and its key advantage here is that it can dissolve starch-derived glucans without exposing cellulose to the harsh alkaline conditions that drive structural change. Swapping caustic extraction for DMSO treatment protects the cellulose fraction from chemical modification, which means the measured residue is more likely to represent the cellulose that was genuinely present in the original sample rather than a partially degraded remnant of it. The trade-off, however, is that DMSO does not remove everything. Some resistant starch, the fraction of starch whose granular structure or chemical modification makes it stubbornly insoluble under ordinary conditions, can survive the DMSO step and contaminate the apparent cellulose measurement.

The solution to the resistant starch problem came from enzymology rather than solvent chemistry. The team employed a mixture of enzymes, including pullulanase, a debranching enzyme that cleaves the alpha-1,6 glycosidic linkages responsible for the branched architecture of starch molecules. By attacking these branch points, pullulanase renders resistant starch accessible to the other amylolytic enzymes in the mixture, allowing the residual starch to be hydrolyzed completely to glucose and washed away. This enzymatic cleanup step is what allows the DMSO-based protocol to achieve the selectivity that caustic extraction provided by brute chemical force, but without the collateral damage to cellulose. The combination of a gentler solvent and a targeted enzyme cocktail means that each class of interfering polysaccharide is removed by the mechanism best suited to it.

One more source of interference remained, and it is specific to fermentation samples: the yeast itself. The Saccharomyces cerevisiae cells that carry out industrial ethanol fermentation are encased in cell walls rich in beta-glucan, a glucose polymer that, despite its similar name and composition, is structurally unrelated to cellulose. In a fermentation intermediate, yeast beta-glucan can be present in quantities that dwarf the cellulose content of the grain, and any measurement that fails to distinguish between these two glucans will attribute the yeast-derived glucose to the cellulose fraction, inflating the result. The researchers solved this by incorporating Zymolyase, a commercially available enzyme preparation well known to microbiologists for its ability to digest yeast cell walls. Zymolyase selectively hydrolyzes yeast beta-glucan, dismantling the cell wall polysaccharide while leaving cellulose untouched, and thereby eliminating the single largest source of false attribution in these samples.

With all three components in place, DMSO to dissolve non-cellulosic glucans, pullulanase and its enzymatic partners to clear resistant starch, and Zymolyase to remove yeast beta-glucan, the protocol delivers a residue that can be confidently identified and quantified as cellulose. The performance of the method was assessed on samples with low cellulose content, which is precisely the regime where analytical precision matters most and where errors are hardest to avoid. The procedure demonstrated excellent reproducibility, with coefficients of variance of 7.14 percent or less. In practical terms, this means that repeated measurements of the same low-cellulose samples clustered tightly around their mean value, giving analysts and process engineers confidence that a change in the measured cellulose number reflects a real change in the process rather than noise in the assay.

Crucially, the method was not validated only on laboratory-prepared mixtures. The team tested it on samples relevant to both laboratory and full-scale plant operations, which is a meaningful distinction in the world of biofuel analytics. Industrial fermentation intermediates contain compounds, particulates, and microbial communities that are difficult to reproduce in a laboratory setting, and an assay that performs well on synthetic samples can still fail on the real thing. By demonstrating the procedure on authentic plant samples, the researchers provided evidence that the method holds up under the conditions where it will actually be used.

The most striking demonstration of the method’s discriminating power came from experiments in which cellulase, the enzyme cocktail that breaks cellulose down into fermentable glucose, was either added to or withheld from the process. When cellulase was included, the analysis showed an average of 0.9 percent of the ethanol in the final product derived from the conversion of cellulose. When no cellulase was added, the method returned a zero response, indicating no detectable cellulose-derived ethanol. This paired result is exactly what a correct assay should produce: a small but measurable signal when cellulose conversion is enzymatically enabled, and silence when it is not. It confirms that the protocol is not merely detecting glucose from starch or yeast glucan and mislabeling it as cellulose-derived, but is genuinely tracking the fate of the cellulose fraction through the fermentation.

For the biofuels industry, the significance of this work extends beyond a single laboratory technique. Grain-based ethanol plants are increasingly interested in understanding and quantifying every stream of carbohydrate flowing through their processes, both to maximize yield and to evaluate whether cellulosic conversion can be layered onto existing starch-based operations. If a plant adds cellulase to its process, it needs a reliable way to verify that the enzyme is actually converting cellulose to ethanol, and by how much. An assay that overstates cellulose conversion because it counts yeast beta-glucan or resistant starch as cellulose would lead to flawed economic decisions and misallocated engineering effort. Conversely, an assay that loses cellulose during sample preparation would understate conversion and could cause a viable process improvement to be abandoned. The DMSO, pullulanase, and Zymolyase approach gives the industry a measurement it can trust at the low concentrations where these questions are decided.

The study, which received support from the U.S. Department of Energy’s Office of Science and the Office of Energy Efficiency and Renewable Energy’s Bioenergy Technologies Office, with nuclear magnetic resonance work performed at the University of Georgia’s Complex Carbohydrate Research Center, ultimately makes a simple but consequential claim: that a cellulose method built on DMSO, pullulanase, and commercially available Zymolyase provides a complete and accurate view of cellulose content, composition, and conversion in industrial fermentation processes. By replacing a lossy chemical extraction with a sequence of selective, well-characterized dissolution and enzymatic steps, the researchers have turned a persistent attribution problem into a solved one. For a field in which the difference between 0 and 0.9 percent cellulose-derived ethanol can determine whether a new process pathway is pursued, that kind of analytical clarity is not a technical nicety. It is the foundation on which the next generation of grain fermentation chemistry will be built.

Subject of Research: Analytical quantification of cellulose in grain fermentation intermediates by selective removal of yeast glucans

Article Title: Improving cellulose attribution by selectively removing yeast glucans from grain fermentation intermediates

Article References: Sluiter, J., Michel, K., Moxley, G., Gogerty, D., Plocher, B., & Tille, M. (2026). Improving cellulose attribution by selectively removing yeast glucans from grain fermentation intermediates. Biotechnology for Biofuels and Bioproducts. https://doi.org/10.1186/s13068-026-02820-z

Image Credits: AI Generated

DOI: 10.1186/s13068-026-02820-z

Keywords: cellulose, yeast beta-glucan, Zymolyase, DMSO, pullulanase, resistant starch, grain fermentation, biofuels, ethanol, cellulase, analytical chemistry, biomass conversion