What a mushroom polysaccharide number counts

"Polysaccharides" sounds like the mushroom part of a mushroom supplement. Starch is a polysaccharide too, and so is the cellulose in an oat. A 2025 study of chaga products found the grain-grown ones were 33 to 68% alpha-glucan, while wild chaga was under 2%. The standard beta-glucan kit carries its own warning about grain. Here is how to read the number.

I formulate functional-mushroom supplements, so this is my own category's arithmetic, and I will try to write it the way I would want it written about me. A month ago, in Report 129, I said a polysaccharide percentage is "a category broad enough to include the starch from a grain substrate." That was a claim. This report is the measurement behind it.

Three sugars that all count

A polysaccharide is any long chain of sugar units. The word says nothing about which sugar, how the units are linked, or where they came from. For mushroom products, three kinds matter.

Fungal beta-glucans. Glucose chains with beta-(1,3) linkages and beta-(1,6) branches. These are the cell-wall polysaccharides the mushroom literature is mostly talking about when it talks about polysaccharides.

Starch. An alpha-glucan, and the main storage carbohydrate in grain. Rice, oats and sorghum are mostly starch.

Cereal beta-glucans and cellulose. Grains carry beta-glucans of their own, with beta-(1,3) and beta-(1,4) linkages, plus cellulose, which is beta-(1,4). Structurally different from the fungal kind. Still beta-glucan, and still polysaccharide.

Many mushroom products are not grown as mushrooms. The fungus is grown as mycelium on cooked grain, and the whole mass, grain included, is dried and milled. The grain does not leave. So the question for any polysaccharide figure is simple: how much of it is fungus?

The chaga measurement

The clearest recent data comes from a study of chaga published in March 2025 in the International Journal of Molecular Sciences (open access). Chaga is a slightly unusual case: it is not a mushroom cap but a woody canker the fungus Inonotus obliquus forms on birch, and the paper notes it has never been successfully cultivated. Products sold as chaga are therefore either wild canker or mycelium grown on something else.

The authors compared six wild chaga samples from China, Alaska, Quebec, Ontario and Finland; pure I. obliquus mycelium grown in liquid culture; cooked oats, brown rice and sorghum as reference substrates; one commercial chaga canker extract; and four commercial mycelium-on-grain "chaga" products bought online. They measured alpha- and beta-glucans with Megazyme's yeast and mushroom beta-glucan kit (K-YBGL), and checked for starch with iodine.

The alpha-glucan result is the headline. Wild chaga held 0.8 to 1.1% alpha-glucan. The plain grains held 46 to 74%. The four grain-grown commercial products held 33.1 to 68.4%. In other words, by this measure the products sat much closer to the grain they grew on than to the organism on the label.

The beta-glucan result is quieter but tells the same story. Wild chaga came in at 5.7 to 11.9%. The grain-grown products came in lower, 1.0 to 6.9%, and they tracked their substrates: about 1% for the rice-based material and about 5% for the oat-based, close to the grains themselves. The authors conclude that these products' polysaccharides "likely originate from the cereal substrate, rather than fungal biomass."

Now run the label arithmetic yourself. Add the alpha-glucan and the beta-glucan of one of those products and you get a large "polysaccharide" figure, most of which is starch. Report only the total and the total looks impressive.

The mycelium is not the villain

It would be easy to read this as "mycelium bad," and the data does not say that. The pure mycelium, grown in liquid with no grain, had the highest beta-glucan in the whole study, 14.4%. It also had 15.2% alpha-glucan, which the authors attribute to glycogen-like storage sugar, not starch.

That is where the iodine test earns its place. Lugol's iodine turns starch blue-purple. Every grain-grown product turned blue to purple, and the color disappeared after the samples were digested overnight with alpha-amylase, the enzyme that breaks starch down, which confirms starch was the cause. The wild chaga did not react, and neither did the pure mycelium, despite its 15.2% alpha-glucan. The authors call starch "a reliable marker for detecting grain-derived material."

So the distinction that matters is not mushroom versus mycelium. It is fungus versus substrate. The same alpha-glucan percentage can mean fungal storage sugar or leftover grain, and it takes a second test to tell them apart. The paper is careful to call Lugol's "primarily qualitative," which is right: it tells you starch is there, not how much.

One more measurement sits in my own lane. Chaga's dark color is melanin, and melanin absorbs broadly across the ultraviolet and visible spectrum. In alkaline extracts measured at 500 nm, wild chaga gave absorbances around 0.49 even after a twentyfold dilution, while the grain-grown products (and the lab-grown mycelium) read 0.031 to 0.049 undiluted. A spectrometer cannot read a label, but it can see that a "chaga" powder has almost none of the pigment that makes chaga black.

The beta-glucan kit's own fine print

Beta-glucan is the better number to ask for. It is not immune to the substrate either, and the kit tells you so.

The method behind K-YBGL, published by Barry McCleary and Anna Draga of Megazyme in the Journal of AOAC International in 2016, measures total glucan by acid hydrolysis, measures alpha-glucan separately by enzymes, and reports beta-glucan as the difference. Subtraction is a fine method as long as everything that is not alpha-glucan really is fungal beta-glucan. Grain breaks that assumption. The kit's current instructions say:

This method is NOT applicable to the analysis of yeast/mushroom β-glucan in the presence of other β-glucans, for example cellulose (1,4-β-D-glucan).

The chaga authors make the same point about grain-containing products, writing that "as the manufacturer explicitly warns, products containing grain will elevate results due to detection of cereal β-glucans and cellulose." So a beta-glucan percentage on a grain-grown product is an upper bound on the fungal beta-glucan, not a measurement of it. Some of it is oat.

The same instructions put the kit's limit of quantification for solid samples at 1.5%. The rice-based product's roughly 1% beta-glucan sits below that line. That is not a criticism of the study, which reported what it measured. It is a reminder that a low result near a method's floor is a weaker number than it looks on a chart.

Not just chaga

The chaga authors cite an earlier survey that found the same pattern in reishi. In 2017, a team publishing in Scientific Reports tested 19 reishi products bought in the United States. Starch-like polysaccharides showed up in 13 of the 19. The branched beta-(1,3)-glucan characteristic of reishi was detected in only 5 of 19, and only 5 of 19 matched their labels on the ingredients measured. Different species, different lab, eight years earlier, same arithmetic.

What these papers are not

The chaga study's authors have a stake, and they say so. Five of the six work for Nammex, which their conflict-of-interest statement says "has a financial interest in the production and sale of authentic chaga supplements." The sixth works for Purity-IQ, a testing lab "frequently employed by Nammex." Nammex sells the kind of product that wins this comparison. The numbers come from a commercial kit anyone can buy and a starch test any teaching lab can run, so they are checkable, but you should weigh them knowing who ran them. I am a supplement formulator writing about it, which is a stake of my own.

Four commercial products is not a market survey. The paper does not say how they were chosen beyond "purchased from the internet," and nobody should turn four into a percentage of the category. I am not going to.

None of this measures whether any chaga or mycelium product does anything in a human body. It answers a prior question, what is in the jar, which has to be settled before a study of one material can be stretched to cover another.

Four questions for a polysaccharide claim

Polysaccharide, or beta-glucan? A total polysaccharide figure without a breakdown cannot separate fungal material from starch. Ask for beta-glucan and alpha-glucan as separate numbers.

Which method? "Polysaccharides 30%" means nothing without the assay named. Enzyme kits, acid hydrolysis and older colorimetric methods do not measure the same thing.

What did it grow on? If the answer is grain, ask for a starch result. If there is grain, read any beta-glucan figure as a ceiling, per the kit's own warning.

Near the floor? A result close to the method's limit of quantification deserves less weight than one far above it.

None of these questions requires taking anyone's word for anything, including mine. That is the point of measuring.

Not medical advice. This is educational analysis, not a recommendation — a study is not a prescription. Talk to a qualified clinician before acting on anything you read here. Full disclaimer →

Sources

C. Windsor, A. E. Kreynes, J. S. Chilton, W. A. Chioffi, A. Krishnamurthy and M. Ishii, "Comparative Study of Chaga (Inonotus obliquus) Dietary Supplements Using Complementary Analytical Techniques," International Journal of Molecular Sciences 26(7):2970, published 25 March 2025, DOI 10.3390/ijms26072970, PMCID PMC11988691. Open access under CC BY. (Primary source, opened and read in full via Europe PMC. Source of: the sample set (six wild vouchers, liquid-culture mycelium, oat/brown rice/sorghum references, one canker extract, four mycelium-fermented-grain products "purchased from the internet"); chaga as an uncultivated canker; the alpha-glucan figures (0.8 to 1.1%, grains 46 to 74%, products 33.1 to 68.4%); the beta-glucan figures (5.7 to 11.9%, products 1.0 to 6.9%, about 1% rice-based and about 5% oat-based); pure mycelium at 14.4% beta- and 15.2% alpha-glucan with a negative iodine result; the Lugol's and alpha-amylase results; the melanin absorbances at 500 nm (0.4854 at dilution factor 20; 0.0313 to 0.0492 at dilution factor 1); the use of K-YBGL; and the quoted phrases on cereal-substrate origin, starch as a reliable marker, Lugol's as primarily qualitative, the manufacturer's grain warning, and the conflict-of-interest statement. The paper's HPTLC, NMR and LC-MS results were read but are not used here.)
Megazyme (Neogen), β-Glucan (Yeast and Mushroom) Product Instructions, K-YBGL 09/25, 11 pp. (Primary source, opened and read. Source of the total-glucan-minus-alpha-glucan principle, the quoted applicability warning, and the 1.5% (w/w) limit of quantification for solids. The chaga study used an earlier version, 08/23, which was not seen.)
B. V. McCleary and A. Draga, "Measurement of β-Glucan in Mushrooms and Mycelial Products," Journal of AOAC International 99(2):364–373 (2016), DOI 10.5740/jaoacint.15-0289, PMID 26957216. (Abstract read via PubMed; full text is paywalled and was not read. Cited only for the method's design: total glucan by acid hydrolysis, alpha-glucan by enzymes, beta-glucan by difference.)
D.-T. Wu, Y. Deng, L.-X. Chen, J. Zhao, A. Bzhelyansky and S.-P. Li, "Evaluation on quality consistency of Ganoderma lucidum dietary supplements collected in the United States," Scientific Reports 7:7792 (2017), DOI 10.1038/s41598-017-06336-3, PMCID PMC5552695. (Opened and read in the relevant sections. Source of the 19 products, starch-like polysaccharides in 13 of 19, the branched 1,3-beta-D-glucan detected in 5 of 19, and label agreement in 5 of 19.)
Prior reporting in this publication: Report 129, which lion's mane did you buy; Report 164, what an FTIR match proves. (Context only. No claim in this report rests on them.)

Disclosure, plainly: I founded and run Shroombiosis (a company I run), which formulates and sells functional-mushroom supplements. That is a direct commercial stake in the category this report grades, and the four questions at the end are questions you should put to me as readily as to anyone else. I have no relationship with Nammex, Purity-IQ, Megazyme or any of the authors. Nothing here is sponsored and no link earns a commission; here's the full policy. A recommendation with no stake at all: for performance nutrition, Die Tryin Co. is a fellow combat-veteran-owned brand I'm glad to point people to. I don't own it and earn nothing from the link.