In July 2024, Ms. Deng from Deqing County, Zhejiang Province posted online that an apple in her home that had been forgotten for many days had “gone moldy” and even grew mushrooms!
From the photos she provided, we can see that the apple is basically intact on the outside, but a few white mushrooms have sprouted from the top. This phenomenon is very surprising, because most mushrooms can only grow on soil and rotten wood, and take rotten organic matter as nutrition. This apple looks fine, so how could it grow mushrooms?
Not long after, Ms. Deng received a private message from a doctoral student at the Kunming Institute of Botany, Chinese Academy of Sciences, saying that he wanted to buy the apples for research. Ms. Deng followed the doctor's instructions and wrapped the apples in plastic wrap and put them in the refrigerator. The next day, she put them in a foam box with ice packs.Sent free of charge to the Kunming Institute of Botany, Chinese Academy of Sciences.
Seeing this ups and downs experience, netizens lamented that this apple finally played its scientific research value. The comment area was also full of joy. Some netizens even jokingly called it the “king of fruit fungi”…
Source: A social platform @沛容
Why haven't we seen mushrooms growing on other apples before? What is the scientific value of this mushroom? Let's find out today.
What are mushrooms on an apple?
Through further sequencing and identification, the researchers found that this mushroom is Schizophyllum commune, which is the model species of the genus Schizophyllum and the most common species of the genus. It has extremely tenacious vitality and is widely distributed all over the world. You can find their traces on branches and wood piles in the wild at almost any time of the year.
The split-gill fungus is named for its unique longitudinally cracked gills. It usually likes to grow on withered and rotten wood. It has a strong ability to decompose lignin and is a saprophyte.
In addition, Schizophyllum is also considered a plant pathogen. Its mycelium is extremely active and can infect living trees such as apples, citrus and olives, causing wood rot, blackening of bark and leaf necrosis. This wood rot disease mainly occurs on aging trees with weak disease resistance. There are reports of apple trees infected with Schizophyllum both at home and abroad.
Therefore, a reasonable assumption is thatThe schizophyllum fungus initially infected apple trees, causing them to carry the spores or hyphae of the fungus, and when environmental conditions were suitable (such as the rainy season), they grew on apples.
Schizophyllum fungi growing in the wild. Source: Author
As the “King of Fruit Fungi” has become a hot topic, some netizens have even posted photos of Schizophyllum growing on other substrates.The most unique one is the Schizophyllum fungus growing on garlic.Many people have questions. Isn't garlic a sterilizing agent? How can it grow mushrooms?
In fact, this is the same question as why garlic gets moldy. The main antimicrobial active ingredient of garlic is allicin, but allicin does not exist naturally in garlic cells. Only when the tissue structure of garlic is destroyed by mechanical external force can alliin and alliinase in the body combine to form allicin.
The invasion of fungal hyphae will not cause significant damage to tissue cells, so only a trace amount of allicin can be produced, which is not enough to resist the invasion of fungi. Therefore, the antibacterial property of garlic cannot prevent its own decay or the infection of Schizophyllum.
Source: References[5]
Why do non-perishable apples grow mushrooms?
In fact, after cutting open the apple with mushrooms, you can see that the hyphae have already infected the inside of the apple and are gradually expanding outward. The inside of the apple is obviously rotten. If you look closely at the top of the apple where the mushrooms grow, you can still find signs of deterioration on the skin of this seemingly intact apple.
Source: A social platform @I really can’t drink anymore
Food spoilage is caused by bacteria and various fungi. When these microorganisms break down food, they produce various wastes that may be harmful to human health. For example, Aspergillus flavus likes to multiply in large numbers on grains. The aflatoxin it produces is considered to be the most toxic and strongest liver carcinogenic natural compound.
Life experience tells us that apples are a very durable fruit that can be stored for several months without spoiling, but they will lose moisture and become shriveled. So why did this happen to this apple?
It turns out that apples secrete a layer of wax during their growth, which can effectively prevent external microorganisms from invading the flesh. However, the concave part of the apple stem is a weak point that leads directly to the core, so it is most susceptible to microorganisms invading, and Schizophyllum also chooses this place to grow.
Apple's shape Source: References[6]
If you observe carefully, you will find that mushrooms in nature like to grow in the cracks of wood, preferably in places with wounds, which makes it easier for mushroom mycelium to invade the interior of the substrate.
Therefore, apples and other fruits with wounds should be eaten as soon as possible, otherwise they will go bad more easily. When storing apples on a daily basis, you can put them in the refrigerator. Low temperature can inhibit the growth of microorganisms and extend the shelf life.
Apples are edible, and so are schizophyllums. So can apples with schizophyllums still be eaten? The answer is no! Food spoilage involves a variety of microorganisms. Although schizophyllums may have the main advantage, there are probably other bacteria and fungi that exist, and the substances they produce during metabolism may be harmful to health.
Taking a step back, even if there are only Schizophyllum in the apple, wouldn't eating apples covered with Schizophyllum hyphae be equivalent to eating mushrooms raw? It is still not recommended.
It turns out that we have eaten schizophyllum before!
As early as 2000, the people in Yunnan, my country, had the habit of eating Schizophyllum, which was vividly called “white ginseng”. The classic way to cook it is “steamed eggs with white ginseng”, or it can be fried directly, which is delicious and nutritious, but the texture is hard, so it needs to be soaked in advance.
People in Mexico, India and other places also have the habit of eating schizophyllum. One advantage of schizophyllum compared to other edible mushrooms is thatIt is hard and elastic, not easy to rot, and easy to sellAt present, due to the limited output of artificial cultivation, the price of Schizophyllum is relatively high, and the price of dry products can reach 50 yuan per catty.
Schizophyllum growing in cracks of rotten wood Source: References[7]
After tasting it personally, the researchers found that the Schizophyllum fungus grown on apples did not taste like apples. This result is actually predictable.
The flavor substances in mushrooms include non-volatile free amino acids, soluble sugars, flavor nucleotides, etc. Volatile flavor substances include sulfur-containing compounds and alcohols, ketone compounds, aldehydes, esters, etc. The production of these substances is controlled by genes, and the same is true for the flavor substances in apples.
In different growth matrices, due to differences in environmental conditions, the same mushroom may secrete more or less of these flavor substances, thus affecting the taste of the mushroom, but it is unlikely to cause changes in the genes that produce these flavor substances, let alone the directed possession of genes that produce apple flavor substances.
Let’s take an example from plants: some watermelons are grafted onto pumpkin vines. This is to utilize the pumpkin’s developed root system to absorb more nutrients from the soil for the growth of the watermelon. The resulting watermelons will be more delicious, but will not have the flavor of pumpkin.
Why do researchers collect Schizophyllum fungi from apples?
The goal of edible fungi breeding is to obtain high-yield, high-quality, high-resistance and high-content biologically active substances varieties. Under natural conditions, some wild edible fungi will mutate, and the beneficial mutations can be accumulated and utilized to obtain new varieties that people need.
This important breeding method is called “artificial selection breeding”. Excellent shiitake mushroom (Lentinula edodes) varieties such as 7401, Guangxiang No. 5, 241 and 8210 were all obtained through artificial selection. This is why researchers engaged in edible fungus cultivation will widely collect wild edible fungus resources of a single species.
What is clear now is that the mycelium of Schizophyllum growing on this apple is highly active and grows fast. Next, we need to conduct cultivation experiments to see if it can produce high yields. In fact, for Schizophyllum, it may be more important to breed a variety that is not so hard, so next we need to evaluate its taste.
Source: A social platform @I really can’t drink anymore
There is a more efficient method in edible fungus breeding technology – radiation mutagenesis breeding, which uses physical or chemical mutagens to treat cell populations, increase their mutation rates, and then select mutant strains that meet the breeding goals from the population.
The mycelium of Schizophyllum has been sent to space many times, and space radiation has been used to change its genetic characteristics, thereby selecting Schizophyllum with better taste for the market.
It is worth noting that Schizophyllum is also a common human pathogen, and its morphology after infecting people is similar to that of mold. Most cases involve the respiratory tract, including bronchopulmonary disease and sinusitis, and occur in both normal and impaired immune function.
This reminds us that when collecting and handling Schizophyllum,Do not put it under your nose and smell it to avoid inhaling the spores of the schizophyllum.
references
[1]Mao Xiaolan, 2000. Macrofungi of China. Henan Science and Technology Press.
[2]Yu Zipeng, Li Ningyang, Gong Zhiqing, et al. Research progress on flavor substances of edible fungi and their detection technology and application[J]. Food Industry Science and Technology, 2024, 45(02): 373-379. DOI: 10.13386/j.issn1002-0306.2023020269.
[3]Fu Lizhong, Wu Xueqian, Wei Hailong, et al. Current status and prospects of research on edible fungi breeding technology in my country[J]. Journal of Edible Fungi, 2005, (03): 63-68. DOI: 10.16488/j.cnki.1005-9873.2005.03.012.
[4]Chowdhary A, Kathuria S, Agarwal K, et al. Recognizing filamentous basidiomycetes as agents of human disease: a review[J]. Medical Mycology, 2014, 52(8): 782-797.
[5]https://mp.weixin.qq.com/s/kvbog7_IoIEyPBRx1iVEog
[6]https://en.wikipedia.org/wiki/Apple
[7]https://en.wikipedia.org/wiki/Schizophyllum_commune
Planning and production
Author: Rao Gu, School of Life Sciences, Nanjing Normal University
Review丨Zeng Hui, Director of the Edible Fungi Research Institute, Fujian Academy of Agricultural Sciences
Planning丨Fu Sijia
Editor: Yinuo
Proofread by Xu Lai and Lin Lin