By: Jenny (Y13)
Do you enjoy murder mysteries, especially when the murderer uses poisons? Are you used to all the strychnine, arsenic, and cyanide’s appearances in mystery fictions, and are looking for something different? In this article, I will look at some more accessible everyday fruits, that if not careful, might accidentally kill you. The compounds that are present in these fruits are not poisonous on their own, but in the presence of certain other molecules - their accomplice, which are pretty innocent on their own - would lead to some severe reactions, even death if untreated.
As you can see from the title, such fruits exist all year round. Persimmon is my pick for autumn/winter, which I will explore further in this article. If you are interested in completing the other half of the year (spring/summer), lychee and its absurd ability to decrease blood sugar levels is a good start.
While many different persimmon varieties are growing all around the world, they can be divided into 2 big groups – astringent and non-astringent. Astringent persimmons, such as Hachiya and Rojo Brillante, are known as soft persimmons – they are meant to be eaten when they are fully ripe. If you accidentally take a bite of an astringent persimmon while it is still firm and not yet ripe enough, you will experience a bitter and dry puckering sensation in your mouth that makes you want to spit it out immediately. Non-astringent persimmons, such as Fuyu and Sharon, are crunchy on the other hand. Non-astringent persimmons won’t cause any unpleasant reaction and can be consumed hard or soft. The majority of persimmons you can find in UK supermarkets are non-astringent persimmons.
The substance that acts as a villain in persimmon is tannin, which is a water-soluble polyphenol that is present in the cells of many plant species. You can also find it in wine, where it plays the role of adding bitterness and astringency (Wine Folly, n.d.). Tannin shrinks the mucus membrane in the mouth and throat, causing this dry mouth sensation. But why doesn’t eating other fruits cause the dry mouth sensation if tannin is also present? The answer all comes down to dosage, i.e. the amount of tannins present.
Indeed, graphs, pomegranates, apples and many other fruits all contain tannins, but tannin concentrations in persimmons are significantly higher than all of them. For example, tannin concentrations in persimmon juice are 2 times greater than in grape juice, 10 times greater than in pomegranate juice, and 40 times greater than in apple juice (Prommajak, Leksawasdi and Rattanapanone, 2020). Tannins tend to accumulate in the skin of fruits. This explains why grape juice also has a relatively high tannin level – grapes have a high surface area to volume ratio, so more skin is being used in the juice produced per unit volume compared to other fruits. This is also why you might develop a dry mouth sensation when you are chewing graphs with thick skin.
The significant difference in soluble tannin levels of astringent and non-astringent persimmons explains the difference in experience while not yet fully ripe. As you can see in the diagrams below (Chung Gyoo Park et al., 2004), in non-astringent (sweet) persimmon, soluble tannin is reduced naturally during the growing season and ripening. While in astringent persimmon, soluble tannin level steadily increases during the growing season and a high level of soluble tannin is maintained when it is not fully ripe. This supports the theory: astringent persimmons need extra time for the tannins to be broken down before it can be
eaten, while non-astringent persimmons already have a low tannin level, therefore can be eaten straight off the tree.
How can tannin in persimmon kill you? Dry mouth alone is certainly not sufficient – something more severe happens deeper into the digestive system. Persimmon tannins can react with stomach acid to form coagulation or “food lump”, which consists polymerised fibres, other vegetable substances and proteins. These coagulations are called persimmon phytobezoars, which might cause nausea, vomiting, and abdominal pain. When these phytobezoars grow too big that your digestive system can’t manage or pass them out, they start to block the gastrointestinal tract, causing intestinal obstruction, upper gastrointestinal
bleeding, even gastric outlet obstruction (Tan et al., 2016). Persimmon phytobezoar is the hardest phytobezoar of all due to its tough consistency (Tan et al., 2016), thus extra difficult to be broken down or pass it out without artificial interference.
Apart from the high concentrations of the villain tannin present in not yet fully ripe astringent persimmons, persimmon is a delicious fruit with many positive connotations. In Mandarin Chinese, persimmon, 柿 (shì), is a homonym for thing, 事 (shì). So eat a deliciously sweet persimmon of your choice, and may good things happen to you in the new year! 2024, 好柿发生!
Reference
Chung Gyoo Park, Kyu Chul Lee, Dong Woon Lee, Ho Yul Choo and Albert, P. (2004). Effects of Purified Persimmon Tannin and Tannic Acid on Survival and Reproduction of Bean Bug, Riptortus clavatus. Journal of Chemical Ecology, 30(11), pp.2269–2283. doi:https://doi.org/10.1023/b:joec.0000048788.35693.23
Nelson, R. (2021). Yes, Persimmons CAN KILL YOU! - Untamed Science. [online] untamedscience.com. Available at: https://untamedscience.com/blog/yes-persimmons-can-kill-you/#google_vignette [Accessed 21 Jan. 2024].
Prommajak, T., Leksawasdi, N. and Rattanapanone, N. (2020). Tannins in Fruit Juices and their Removal. Chiang Mai University Journal of Natural Sciences, 19(1), pp.76–90. doi:https://doi.org/10.12982/cmujns.2020.0006
Tan, F., Mo, H., He, X. and Pei, H. (2016). An unusual case of gastric outlet obstruction caused by multiple giant persimmon phytobezoars. Gastroenterology Report, 7(1), pp.74–76. doi:https://doi.org/10.1093/gastro/gow042
Teng, T., Tan, Y. and Shelat, V. (2019). Persimmon fruit causing simultaneous small bowel and stomach obstruction. Singapore Medical Journal, 60(10), pp.550–550. doi:https://doi.org/10.11622/smedj.2019132
Wine Folly. (n.d.). What Are Tannins In Wine? [online] Available at: https://winefolly.com/deep-dive/what-are-wine-tannins/# [Accessed 21 Jan. 2024]. Tannin in wine.