The standard advice is to ignore "polysaccharides" on a mushroom label and look for a beta-glucan figure instead. We've given that advice ourselves, in three separate articles. It's right as far as it goes — and it stops one step short, because the industry-standard beta-glucan assay also counts the beta-glucan in oats and barley. The number you were told to trust can be padded by the same grain substrate it was supposed to expose.
"Polysaccharides" includes starch, so a 40% polysaccharide claim can be mostly grain. Beta-glucan is the better number: supplier testing puts Trametes fruiting body at 49.3% beta-glucan against 6.7–9.1% for grain-grown mycelium, which carried 24–45% starch. But the standard Megazyme assay measures 1,3:1,6 fungal glucan and 1,3:1,4 cereal glucan together, so a grain-heavy product can still report a respectable beta-glucan figure. Ask for the alpha-glucan number too — that's the one that gives the substrate away.
This article is narrower than our general label-reading guide. It's only about the measurement: what the number is, how a lab produces it, and where it can still mislead you.
What's the Difference Between a Polysaccharide and a Beta-Glucan?
Category and specificity. Polysaccharide is a chemical class — any long chain of sugar units. Starch is one. Cellulose is one. So is glycogen. Beta-glucan is a specific member of that class, and it's the one with the immune literature behind it.
Which means "polysaccharides: 40%" tells you the product is 40% long sugar chains. It doesn't say which. For a mushroom grown on rice or oats, the honest translation is often "40% of this is carbohydrate, and much of it is the grain".
Why Is Starch the Real Story?
Because grain-grown mycelium products carry a lot of it, and the numbers aren't subtle. Supplier testing reports mushroom fruiting bodies at under 3% starch on average, while mycelium grown on grain averages 35 to 40% (Nammex).
Set the two side by side and the pattern is consistent across species.
| Species | Fruiting body beta-glucan | Fruiting body starch | Mycelium-on-grain beta-glucan | Mycelium starch |
|---|---|---|---|---|
| Trametes | 49.3% | 0.1% | 6.7–9.1% | 24.6–44.8% |
| Cordyceps militaris | 34.4% | 1.7% | 1.5–7.6% | 1.7–64% |
| Maitake | 32.4% | 1.6% | 3.5–6.4% | 39.9–44.5% |
| Shiitake | 28.2% | 0.7% | 7.2% | 38.9% |
| Reishi | 28.1% | 0.1% | 1.1–7.3% | 45.2–51.4% |
One caveat worth stating plainly: this testing was commissioned by a fruiting-body ingredient supplier, so the party that produced the numbers benefits from the conclusion. The figures line up with independent academic work on substrate carryover, and they're the most detailed public dataset available — but read them knowing who paid for them.
How Is Beta-Glucan Actually Measured?
By subtraction, which is where the trouble starts. There's no AOAC official method written specifically for mushroom beta-glucans. The accepted approach uses the Megazyme K-YBGL kit to measure total glucan and alpha-glucan separately, then reports beta-glucan as the difference between them.
Alpha-glucan is essentially the starch reading. So a certificate of analysis that gives you both numbers is genuinely informative: high alpha-glucan means grain, whatever the label says about fruiting body. Our beta-glucan guide covers what the resulting percentages mean per species.
Where Does the Standard Advice Break Down?
Here. Fungal cell walls are built from 1,3:1,6 beta-glucan. Cereal grains — oats, barley, wheat — contain 1,3:1,4 beta-glucan. Different linkage, different molecule, and the immune literature is about the fungal one.
The catch is that the standard kit doesn't separate them. Megazyme's own support documentation states the K-YBGL kit measures 1,3:1,6 and 1,3:1,4 beta-D-glucans. A product grown on oats can therefore report a beta-glucan percentage that includes the oats.
There's a suggested workaround — run a second, mixed-linkage kit and subtract — and it isn't clean either. Megazyme notes that beta-glucosidase acts along the 1,3 chain until it hits a branch point, so some fungal 1,3:1,6 glucan gets measured by both kits and subtracted twice. No routine commercial method cleanly isolates fungal beta-glucan in a grain-grown product.
So What Number Should You Actually Ask For?
Alpha-glucan. It's the one nobody advertises and the one that settles the question. A fruiting-body product should be near zero — 0.1% for reishi and Trametes in the table above. Anything in the tens of percent is grain, regardless of what the beta-glucan figure says or what the front of the bottle claims.
Read as a pair, the two numbers are hard to fake. A high beta-glucan with a low alpha-glucan is a real fruiting-body extract. A moderate beta-glucan with a high alpha-glucan is myceliated grain wearing a respectable number.
Why Do Extract Percentages Confuse the Comparison?
Because a percentage needs a denominator, and labels rarely give you one. A 30% beta-glucan figure means something quite different for raw dried mushroom than for a concentrated extract, and different again for a capsule that blends extract with filler.
Work in milligrams instead. Multiply the beta-glucan percentage by the daily dose of mushroom material, and you get the only figure that compares across products. A 15% extract at 2 grams a day delivers 300 mg of beta-glucan. A 30% extract at 500 mg a day delivers 150 mg, despite the better-looking percentage.
That arithmetic reorders a lot of shelves. It's also why extraction ratios like "10:1" belong nowhere in this calculation — a ratio describes how much material disappeared, not how much of anything arrived.
Does a High Beta-Glucan Always Mean a Better Product?
No, and this is worth separating from the fraud question. Beta-glucan is the relevant marker when you're buying for immune support — Trametes and reishi earn their reputations through that fraction.
It's much less relevant for lion's mane, whose cognitive research is about hericenones and erinacines rather than glucans. Optimising beta-glucan there means optimising a variable no cognition trial measured, as our lion's mane label guide works through. The right number depends on why you're buying.
Why Don't Regulators Fix This?
Because in most markets these are food supplements, not medicines, and nothing requires a manufacturer to declare either glucan figure. A label can say "mushroom extract" and stop there, legally.
That leaves the whole system running on voluntary disclosure, which is exactly why a company that publishes full certificates of analysis is telling you something meaningful before you've read a single number. The willingness to be checked is itself the signal. A brand that won't send you a certificate has answered the question.
How Do You Audit a Label in Two Minutes?
- If it says "polysaccharides" and nothing else, treat the number as uninformative and move on.
- If it gives beta-glucan, that's better — but it's not the end of the check.
- Ask for the alpha-glucan figure. Near zero means fruiting body; double digits mean grain.
- Check whether a certificate of analysis exists at all, and whether it names the assay method.
- Match the material claim against the numbers. "Fruiting body" plus 40% alpha-glucan is a contradiction.
- Decide whether beta-glucan is even the right metric for your goal.
Frequently Asked Questions
What does "polysaccharides 40%" mean on a mushroom label?
That 40% of the material is long-chain carbohydrate of some kind, including starch. For grain-grown mycelium products, which average 35 to 40% starch, that figure can largely be measuring the substrate rather than the mushroom.
Is beta-glucan the number to look for?
It's better than polysaccharides, but not sufficient on its own. The standard Megazyme assay counts cereal 1,3:1,4 beta-glucan alongside fungal 1,3:1,6, so grain can inflate it. Ask for alpha-glucan as well.
What is a good beta-glucan percentage?
It depends on species. Supplier testing puts Trametes fruiting body at 49.3%, cordyceps at 34.4% and reishi at 28.1%, against single digits for the grain-grown versions. Lion's mane runs far lower and that's normal.
What does alpha-glucan tell you?
Substrate. Fruiting bodies test near zero — 0.1% for reishi and Trametes — while mycelium-on-grain products run from 25% to over 50%. It's the single most revealing number on a certificate of analysis, and almost nobody puts it on a label.
Are cereal beta-glucans useless?
Not useless, just different. Oat beta-glucan has genuine cholesterol-lowering evidence behind it. It simply isn't the branched fungal molecule the mushroom immune research is about, and it shouldn't be counted as if it were.
Can you convert a polysaccharide figure into a beta-glucan one?
No. There's no fixed ratio between them, because the split depends entirely on substrate and species. A fruiting-body extract might be almost all beta-glucan, while a grain-grown product with the same polysaccharide number could be mostly starch.
Shop
Everything we sell is fruiting body, which is why our labels don't need a starch discussion. The immunity collection covers the species where beta-glucan is the number that matters, and our capsules collection holds the low-effort formats. Free shipping on orders over €50.
Related Articles
- How to Read a Mushroom Supplement Label
- Lion's Mane Beta-Glucans Guide
- How to Read a Lion's Mane Label
- How to Read a Reishi Label
- Fruiting Body vs Mycelium
- Mushroom Blend vs Single Species
Sources
- Megazyme. β-Glucan Assay Kit (Yeast and Mushroom), K-YBGL — product documentation and technical support notes on 1,3:1,6 and 1,3:1,4 measurement. megazyme.com
- Nammex. Redefining Medicinal Mushrooms — beta-glucan and starch analysis of fruiting body and mycelium-on-grain products. nammex.com