In it they state the following:
A key medicinal compound in mushrooms is 1,3:1,6-β-glucan. It has been found in shiitake, maitake, reishi and other species and has been shown to have anticarcinogenic activity. Without a good test to measure the amount of β-glucan in a mushroom product, regulators and consumers have had no way to judge the quality of the product. Thus mycelial products may be composed of more α-Glucan (from starch in the substrate) than the active components of the mushroom or its mycelium.
As this technique becomes widely used, some of you will be challenged over the accuracy of your product descriptions and the actual utility of your products. You may wish to produce your extracts from fruit bodies and thus eliminate the impact of substrate residuals in your product. Careful selection of the substrate you use to produce the mushrooms can also affect the levels of the beneficial compounds.
And goes on to say:
This demonstrates that mycelial products grown on grain retain a lot of the starch from the grain. The bottom line is that if you want a product high in β-Glucans, you will need to produce it from mushrooms, not grain-based mycelium.
We couldn’t agree more.