Beta-glucans: the source decides the molecule

"Beta-glucan 70%" is not a specification until you know which beta-glucan. The linkage pattern differs by source, and it is the structural detail — not the percentage — that defines what you have bought.

Three different molecules

• Yeast (Saccharomyces cerevisiae) — beta-1,3/1,6 glucan, insoluble, isolated from the cell wall. The 1,6 branching is the structural feature buyers in this segment are usually specifying for.
• Oat and barley — beta-1,3/1,4 glucan, soluble, viscous. A quite different material used mainly for texture and for fibre content.
• Mushroom (shiitake, reishi, maitake) — predominantly beta-1,3/1,6, with structures varying by species and by whether the material is fruiting body or mycelium.

Specifying a percentage without the source and linkage lets a supplier meet the number with an entirely different molecule. This happens.

The mycelium-on-grain question

A large share of mushroom material on the market is mycelium grown on a grain substrate, dried and milled with the substrate included. The resulting powder contains substantial starch, and starch interferes with the older beta-glucan assays — which is precisely how some very high glucan figures on mushroom products come about.

Two protections:

• Specify fruiting body if that is what you want, and require it on the certificate.
• Require an enzymatic assay (the Megazyme-type method) that distinguishes beta-glucan from alpha-glucan. A total glucan figure without the alpha and beta split is not usable, and the alpha figure is what reveals the starch.

What to put on the specification

• Source organism and species, and for mushrooms whether fruiting body or mycelium.
• Beta-glucan content by enzymatic assay, reported with alpha-glucan separately.
• Linkage type, stated explicitly.
• Particle size and solubility, which differ sharply between the yeast and cereal materials.
• Residual protein and ash for yeast-derived material, both indicators of how thoroughly the cell wall was purified.
• Heavy metals — mushrooms and their substrates accumulate them, and this is one of the ingredient classes where it genuinely matters.

The one-line test of a supplier

Ask for the alpha-glucan figure alongside the beta. Suppliers with a genuine, well-purified material send it without hesitation. The request being deflected is itself the answer.