Alpha vs Beta Glucans: Why the Letter Matters

Quick answer on alpha and beta glucans

Both are glucans — chains of glucose molecules — and the difference is how those molecules are linked together. Beta-glucans are the compounds that come from the mushroom cell wall and are what mushroom research is almost entirely concerned with. Alpha-glucans are starch, which in a mushroom supplement usually means the grain the mycelium was grown on. A test that measures both together and reports the total will make a product that is mostly rice look like a product that is mostly mushroom.

The actual chemistry

Glucose molecules can join to each other at different positions and in different orientations. The orientation is what the Greek letter describes.

Alpha linkages produce starch and glycogen — energy storage molecules, readily broken down by human digestive enzymes. Rice, oats and wheat are largely alpha-glucan.

Beta linkages produce structural materials. Cellulose in plants is a beta-glucan. So is the glucan in a mushroom cell wall, specifically in the beta-1,3 and beta-1,6 configuration, which is the arrangement that appears in essentially all the published mushroom research.

Same building block, different joinery, completely different behaviour.

Why this became a labelling problem

Because of how a large share of the mushroom supplement category is actually produced.

Growing mushroom fruiting bodies takes time and space. Growing mycelium on a sterilised grain substrate is faster and cheaper. The problem is that at harvest, mycelium and the grain it has colonised cannot be meaningfully separated — the product is milled together. The result is a powder containing mycelium and a substantial quantity of rice or oats.

That powder is high in polysaccharides, because starch is a polysaccharide. A label can therefore say "40% polysaccharides" and be entirely accurate while describing something that is largely grain.

The honest measurement is beta-glucan specifically, which excludes the starch. The fruiting body versus mycelium question underneath all of this is covered in fruiting body versus mycelium.

How beta-glucan is actually measured

The method matters as much as the number, and there are two broad approaches.

A total polysaccharide assay measures everything that behaves like a polysaccharide. It cannot distinguish mushroom beta-glucan from grain starch, and it is the cheaper test.

An enzymatic assay uses specific enzymes to break down and separately quantify the alpha fraction and the beta fraction. The Megazyme yeast and mushroom beta-glucan kit is the method most commonly cited on reputable certificates, and it reports alpha-glucan and beta-glucan as separate figures.

If a certificate reports beta-glucan by enzymatic assay, somebody paid for the better test. If it reports total polysaccharides, you cannot tell what you are looking at. We publish the enzymatic figure for the extract in Logic on our testing page for exactly this reason.

What a good number looks like

Context matters more than any single threshold, but some rough bearings help.

A quality mushroom fruiting body extract will typically state beta-glucan somewhere above 20%, and better extracts go considerably higher. A mycelium-on-grain powder often lands in low single digits of beta-glucan while reporting a large polysaccharide number.

An alpha-glucan figure reported alongside is a useful tell. A high alpha-glucan percentage in a mushroom product is grain, and a manufacturer willing to report it is being straightforward with you.

The wider question of what standardisation does and does not promise is in what standardized extract actually means, and the compound itself in beta-glucans explained.

Frequently asked questions

What is the difference between alpha and beta glucans? Both are chains of glucose, differing in how the molecules are linked. Alpha linkages produce starch; beta linkages produce structural compounds including the beta-1,3/1,6-glucan of mushroom cell walls.

Is alpha-glucan bad? It is not harmful — it is starch. The issue is that in a mushroom supplement it usually indicates grain substrate rather than mushroom, so you are paying mushroom prices for rice.

Why do labels say "polysaccharides" instead of beta-glucans? Because the total polysaccharide test is cheaper and produces a larger number, since it counts starch alongside beta-glucan.

What beta-glucan percentage should I look for? A quality fruiting body extract typically states above 20%, with better extracts higher. The figure matters less than whether it is beta-glucan specifically, measured enzymatically.

How is beta-glucan measured? By an enzymatic assay that separately quantifies the alpha and beta fractions. The Megazyme yeast and mushroom beta-glucan method is the one most often cited on certificates of analysis.

Does a high polysaccharide number mean a good product? Not on its own. It can describe a product that is mostly grain. Ask for the beta-glucan figure specifically.

Sources

McCleary BV, Draga A. Measurement of beta-glucan in mushrooms and mycelial products. Journal of AOAC International.

National Center for Complementary and Integrative Health. Mushrooms.

National Institutes of Health, Office of Dietary Supplements. Botanical Dietary Supplements: Background Information.

United States Food and Drug Administration. Dietary Supplement Labeling Guide.

These statements have not been evaluated by the Food and Drug Administration. This product is not intended to diagnose, treat, cure, or prevent any disease.