Chemical test in mushroom identification

Chemical tests in mushroom identification are methods that aid in determining the variety of some fungi. The most useful tests are Melzer's reagent and potassium hydroxide.

Ammonia

Household ammonia can be used. A couple of drops are placed on the flesh. For example, Boletus spadiceus gives a fleeting blue to blue-green reaction.

Iron salts

Iron salts are used commonly in Russula and Bolete identification. It is best to dissolve the salts in water (typically a 10% solution) and then apply to the flesh, but it is sometimes possible to apply the dry salts directly to see a color change. For example, the white flesh of Boletus chrysenteron stains lemon-yellow or olive. Three results are expected with the iron salts tests: no change indicates a negative reaction; a color change to olive, green or blackish green; or a color change to reddish-pink.[1]

Meixner test for amatoxins

The Meixner test (also known as the Wieland test) uses concentrated hydrochloric acid and newspaper to test for the deadly amatoxins found in some species of Amanita, Lepiota, and Galerina. The test yields false positives for some compounds, such as psilocin.[2]

Melzer's reagent

Melzer's reagent can be used to test whether spores are amyloid, nonamyloid, or dextrinoid.

  • Spores that stain bluish-gray to bluish-black are amyloid
  • Spores that stain brown to reddish-brown are dextrinoid

This test is normally performed on white spored mushrooms. If the spores are not light colored, a change will not be readily apparent. It is easiest to see the color change under a microscope, but it is possible to see it with the naked eye with a good spore print.

Paradimethylaminobenzaldehyde

In the genus Lyophyllum the lamellae usually turn blue with the application of para-Dimethylaminobenzaldehyde (PDAB or pDAB).

Phenol

A 2–3% aqueous solution of phenol gives a color change in some species when applied to the cap or stem.

Potassium hydroxide

A 3–10% solution of potassium hydroxide (KOH) gives a color change in some species of mushrooms:

Schaeffer reaction

Developed by Julius Schäffer to help with the identification of Agaricus species. A positive reaction of Schaeffer's test, which uses the reaction of aniline and nitric acid on the surface of the mushroom, is indicated by an orange to red color; it is characteristic of species in the section Flavescentes. The compounds responsible for the reaction were named schaefferal A and B to honor Schäffer.[3]

Two intersecting lines are drawn on the surface of the cap, the first with aniline or aniline water, the second with an aqueous solution of 65% nitric acid. The test is considered positive when a bright orange color forms where the lines cross.[4][5][6]

Agaricus placomyces and Agaricus xanthodermus produce false negative reactions.[4][5]

Sometimes referred to as "Schaeffer's reaction", "Schaeffer's cross reaction" or "Schaeffer's test".

Aniline + acid(s)

Kerrigan's 2016 Agaricus of North America P45: (Referring to Schaffer's reaction) "In fact I recommend switching to the following modified test. Frank (1988) developed an alternative formulation in which aniline oil is combined with glacial acetic acid (GAA, essentially distilled vinegar) in a 50:50 solution. GAA is a much safer, less reactive acid. This single combined reagent is relatively stable over time. A single spot or line applied to the pileus (or other surface). In my experience the newer formulation works as well as Schaffer's while being safer and more convenient."[7]

Sulfo-vanillin

Made from sulfuric acid (H2SO4) and vanillin (vanilla). Used in Russula and Panaeolus identification.

References
  1. Ammirati J, Traquair JA, Horgen PA (1985). Poisonous Mushrooms of Canada. Fitzhenry & Whiteside in cooperation with Agriculture Canada. p. 40. ISBN 978-0-88902-977-4.
  2. Beuhler, M; Lee, DC; Gerkin, R (2004). "The Meixner test in the detection of alpha-amanitin and false-positive reactions caused by psilocin and 5-substituted tryptamines". Annals of Emergency Medicine. 44 (2): 114–20. doi:10.1016/j.annemergmed.2004.03.017. PMID 15278082.
  3. Kileci-Ksoll R, Winklhoer C, Steglich W (2010). "Synthesis of schaefferals A and B, unusual phenylhydrazine derivatives from mushrooms of the genus Agaricus". Synthesis. 2010 (13): 2287–91. doi:10.1055/s-0029-1218790.
  4. Hui, Y. H.; Smith, R. A.; Spoerke, Jr., David G. (2000). Foodborne Disease Handbook, Second Edition: Volume 3: Plant Toxicants. CRC Press. p. 745. ISBN 978-0824703431.
  5. Spoerke, David G.; Rumack, Barry H. (1994). Handbook of Mushroom Poisoning: Diagnosis and Treatment. CRC Press. p. 146. ISBN 978-0849301940.
  6. Bresinsky, A; Besl, H (1990). A Colour Atlas Of Poisonous Fungi: A Handbook for Pharmacists, Doctors, and Biologists. CRC Press. ISBN 978-0723415763.
  7. Kerrigan, Richard (2016). Agaricus of North America. NYBG Press. p. 45. ISBN 978-0-89327-536-5.
  • Arora, David "Mushrooms Demystified" 2nd Edition, Ten Speed Press, Berkeley, 1986
  • Jordan, Michael "The Encyclopedia of Fungi of Britain and Europe" Frances Lincoln 2004
  • Kuo, Michael "100 Edible Mushrooms", University of Michigan Press, Ann Arbor 2007
  • Largent, David L., Baroni, Timothy J. "How to Identify Mushrooms to Genus VI: Modern Genera" Mad River Press 1988
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