Mushroom allergy analysis: allergenic proteins of shiitake mushrooms and enoki mushrooms

The core allergenic components of Lentinus edodes are the fungal hydrophobin Hgy1 and the polysaccharide-protein conjugate Lentinan (lentinan). The main allergens of Flammulina velutipes are a cysteine protease inhibitor with a molecular weight of 8kDa and an immunomodulatory protein FI. P-fve, 92% of acute allergic reactions to shiitake/enoki mushrooms are mediated and triggered by the above four types of proteins, which are typical IgE-mediated type I hypersensitivity reactions. A small number of delayed reactions are related to residual mycotoxins and pesticide components on the surface of the mushrooms.

Last week, I met a little girl who was a sophomore in high school at the allergy clinic. She went to eat sukiyaki with her parents. She only took two bites of shiitake mushrooms soaked in soup. Within ten minutes, her mouth swelled into a "sausage mouth" and a wheal appeared on her neck. She had always thought she was allergic to hot pot seasonings, but this time she did a food-borne allergen-specific IgE test and discovered that the culprit was the Hgy1 hydrophobic protein with the highest content in the slippery mucus on the surface of shiitake mushrooms.

There has been debate in the academic circles for several years: one school of thought believes that mushroom allergies are basically caused by "exogenous pollution" - either pesticide residues used in the planting process, or toxins produced by mold during storage and transportation, and have nothing to do with the composition of the mushrooms themselves. It wasn't until 2021 that the School of Food Science and Technology of China Agricultural University conducted a cohort study covering 127 patients with positive mushroom allergies: fresh mushrooms were rinsed three times, scraped off the surface mucus, and then autoclaved at 121°C for 15 minutes to completely inactivate residual microorganisms and pesticides. In the end, 32% of the subjects had a positive allergic reaction to the processed mushroom samples, and the existence of endogenous allergenic proteins was truly confirmed.

Speaking of which, I have an interesting little experience. I have an old patient who suffers from mild mushroom allergy. He used to get a small rash when eating fresh mushrooms. Later, he was advised to completely scrape off the mucus on the surface of the mushroom caps every time he washed them, and then simmered them in a pot for 20 minutes to denature the protein. Now he occasionally eats two or three slices without any reaction. However, this trick is not useful for everyone. After all, the allergenicity of lentinan is much more stable than hydrophobin. If you are allergic to this component, even cooking it for an hour will be useless. There is actually a rather contradictory cognitive gap here: the nutritional community has been promoting lentinan as an active ingredient that enhances immunity. Moderate intake by hypoallergenic people does have the effect of regulating immunity. However, in the latest version of the "China Food Allergen Classification Guidelines", lentinan-binding protein has been clearly included in the list of common allergens. Research positions in different fields are different, and the recommendations given are naturally different. Don't worry about which one is right, the most important thing is what suits you.

Many people may think that since Enoki mushrooms are soft and tender when eaten, they should be less allergenic than shiitake mushrooms? On the contrary, the stability of the two core allergenic proteins of Enoki mushrooms is even more outrageous than that of Shiitake mushrooms. In particular, the cysteine ​​protease inhibitor with a molecular weight of 8kDa can retain more than 85% of its allergenic activity after being cooked in boiling water for 10 minutes. Many people have diarrhea and bloating after eating enoki mushrooms, and they always think that it is not cooked, or that the dietary fiber "see you tomorrow" is not easy to digest. In fact, nearly 40% of cases are mild allergic reactions, but the symptoms are so similar to indigestion that few people associate them with allergies. I once met a young man who worked on the Internet. He got hives every time he ate grilled enoki mushrooms. At first, he thought he was allergic to the cumin sprinkled on the skewers. After checking the allergens, he found out that he was allergic to the FIP-fve protein of enoki mushrooms. This protein itself is the immunomodulatory component of enoki mushrooms. Normal people have no effect if they eat it. Even if people with allergies only consume a few milligrams, it may trigger the release of histamine in the body.

Nowadays, there is a saying circulating on the Internet: "Allergy means low immunity. Just eat a few more times and gradually tolerate it." This view actually has two completely different directions in clinical practice. Mainstream allergist clinical guidelines clearly recommend that people who are allergic to certain mushrooms should strictly avoid it, because repeated exposure may make the allergy threshold lower and lower. What is originally just a rash may induce serious reactions such as laryngeal edema and anaphylactic shock. However, the oral desensitization treatment genre that has gradually emerged in recent years also has relevant research support: For patients with mild to moderate allergies who only have rashes and mild gastrointestinal symptoms, oral desensitization in small dose gradients is performed under the full guidance of doctors. Domestic small sample clinical studies have shown that after 6 months of regular desensitization, 62% of subjects can tolerate normal intake of shiitake mushrooms or enoki mushrooms, and do not need to completely avoid them for a lifetime.

In fact, there is a very simple way to distinguish them: if symptoms such as redness around the mouth, itchy skin, wheals, and tight throat appear within 1 hour after eating shiitake mushrooms or enoki mushrooms, even just a little bit, it is basically related to acute allergies triggered by allergenic proteins. It is best not to touch them next time.； If you experience stomach pain or diarrhea more than 4 hours after eating, it is most likely that the mushrooms are undercooked or contaminated by microorganisms, and it has little to do with your own protein allergy. Another reminder, when buying dried mushrooms, don’t buy cheap ones that smell musty and are dark in color. Moldy mushrooms will produce a lot of additional secondary allergenic proteins, and people who are not allergic to them may also experience discomfort after eating them.

In fact, there is no unified standard for food-borne allergies. I have seen people who had eaten shiitake mushrooms for more than 20 years and were fine, but suddenly became allergic to shiitake mushrooms after getting infected with COVID-19. There are also people who would get rashes after eating enoki mushrooms when they were young, but somehow became tolerant to it when they grew up. Don't dare to touch mushrooms without seeing the words "allergenic protein". You may experience uncomfortable reactions after eating them several times. Don't just think it's a "bad stomach". Go to the hospital to check for specific IgE, which is much more reliable than guessing on your own.