Starchy fillers - Invisible, not to the trained eye
It is very difficult to find quality and cost efficient functional foods made in countries where labour is expensive (like Australia, New Zealand and US) as it requires manufacturers to come up with creative ways to keep their business viable. There are legitimate ways and not so legitimate ways.
Amongst the legitimate ways are cutting the "middle man" (farmer direct to customer), increase production efficiency, invest more in product quality rather than marketing it etc...
Amongst the not so legitimate ways is to add filler to their products. But... what is a filler?
Fillers are inert compounds added to an active substance - Sometimes with good intentions, like making it easier to fill capsules. But sometimes, with the intention to add dead weight to a product.
For example, some suppliers would still name their products as "mushroom powders" but they add something else to give it more weight and sell it at mushroom prices. One of the most common fillers used is starch as they have no colour, no flavour, are not toxic and are dense (so little volumes add lots of weight).
Fortunately, there is a cheap DIY test you can do at home to find out if a product you purchased is riddled with starches. All you need is Iodine tincture that can be purchased on ebay or pharmacies.
Iodine has been used for ages as a starch indicator - It usually has a brown colour but becomes deep blue / practically black when it reacts with starches. The one I use is "gold cross iodine tincture" but you can find other brands. Just note there are other iodine products in the market (like povidone-iodine solutions) that may not work as starch indicators as well as iodine tinctures.
Start by dropping iodine tincture over known starches like wheat flour, potatoes, bread etc... So you have an idea of the colour iodine takes when it is dropped on a product that has very high levels of starches. Then you can start checking your products.
See below some pictures of iodine tincture dropped on "mushroom" powders riddled with starches that I bought in the market compared against real mushrooms and rice flour (pure starch, used as a reference):
These pictures show that, not only some "mushroom" powders have starches but they have significant levels of starches (the iodine drop turns VERY dark). You can even play around mixing flour and fine sand at 50/50, 70/30 etc... proportions and check the intensity of the dark colour - That would give you a reference of starch concentration (50%, 70% etc...) to compare against a product you are testing, ultimately allowing you to find out what is the approximate concentration of starch in your product. Or just keep it simple - if iodine gets very dark, there is a lot of starch in the product you are testing.
In case of doubt, leave the powder stained by iodine to rest for 24h. In case the iodine reacted to starch, it will be a stable dark colour no matter how long you leave it there. If there are no starches, the iodine tincture solvent will evaporate and all that will be left behind is just a tint of brown from the intact iodine.
Given mushroom powders are usually at the $50 mark and are purchased on a regular basis, investing $8 in bottle of iodine tincture should be a no brainer... And it can be used to check other products you might be purchasing - not only mushroom powders.
When it comes to our nutritional needs, our own research to find products that are right for us should come before trusting someone else - And if you haven't come across the iodine test yet, your research was not complete... hopefully, you still have time to fix it and stop purchasing starch for the price of real mushrooms.