Plant toxins induced food poisoning has been thoroughly documented for decades. The majority of plant species in the world are not edible, largely owing to the existence of toxins they produce. Other than physical defense like thorns, spines and prickles, living plants also produce chemical compounds, secondary metabolites, which function as plant toxins. These toxins are produced naturally to defend against consumption by predators, for instance, human, herbivores, insects or microorganisms. Over the millennia, through the process of natural selection, plants have evolved the means to produce a vast and complicated array of chemical compounds, from small organic molecules to large peptides and proteins, that are deposited in various parts of plant, such as stem, leaves, flower sap, root or plant oil.
The classes of plant toxin include pyrrolizidine alkaloids (Asteraceae, Fabaceae, Boraginaceae); cyanogenic glycosides (cassava, sorghum, stone fruits, bamboo roots, almonds); glucosinolates (cruciferous vegetables, rapeseed, mustard, horseradish); isothiocyanates (cruciferous vegetables like broccoli, cabbage, cauliflower); lectins (kidney beans); glycoalkaloid (tomatoes, potatoes, eggplants) and furanocoumarins (parsnips, celery roots, citrus plants). These toxins are responsible for causing most of the food poisoning that often lead to victim experiencing negative effects ranging from allergic reactions to gastrointestinal disorders such as severe stomachache and diarrhea. Apart from that, consumption of plant toxins can result in long-term health consequences (effects on immune, nervous and reproductive system and cancer). Also, plant toxins that are of extreme potency can result in death of the poisoned victim (i.e. leaves of tobacco plant constitute alkaloids toxin, nicotine and anabasine).
Food poisoning normally occurs upon ingested inedible plant that contains heat-resistant potent toxins, or edible plant that did not undergo proper processing or cooking. Hence, an advanced processing technique is needed to detoxify and destroy plant toxins in plants before eating or used as medical herd. WHO, in collaboration with FAO, are monitoring the food supplies to ensure the level of plant toxins are kept at bare minimum.
Food poisoning caused by consumption of poisonous mushroom is termed as mushroom poisoning. Together with plants, mushrooms have developed their own self-defense mechanism as a result of million years’ worth of evolution. There are thousands of mushroom species, of which, 100 of them can cause symptoms upon swallowed by humans, and only about 15-20 mushroom species are potentially lethal when ingested.
The toxins that produced naturally by the fungi themselves are used against other organisms to shield their fruit bodies from being consumed before they can sporulate. Most poisonous mushrooms cannot be detoxified by cooking, canning, freezing, or any other means of processing. Thus, the only means to reduce the chances of mushroom poisoning is to avoid eating any wild mushrooms, unless it is identified as non-poisonous.
The toxins produced by mushrooms are amatoxin (death cap, destroying angel, autumn skullcap, fool’s mushroom); hydrazines (false morel); orellanine (sorrel webcap mushroom); ibotenic acid and muscimol (fly agaric, panthercap); muscarine (Inocybe, Clitocybe); and psilocybin (Psilocybe, Panaeolus, Copelandia, Gymnopilus, Conocybe, Pluteus). Mushroom poisoning often lead to vomiting, diarrhea, confusion, visual disturbances, salivation, and hallucinations in victim. In severe cases, kidney failure may result and leads to death several weeks post-poisoning. Mushroom poisoning poses a real cause for concern in veterinary clinical toxicology because of the high mortality rate. Most of the mushroom poisoning cases occurred due to misidentification of the poisonous mushrooms by an amateur mushroom hunter. Hence, not only FAO/WHO are working on evaluating the health risk from natural toxins in food, North American Mycological Association are encouraging people to assist in the identification of mushrooms by reporting animal mushroom poisonings case.
Toxins that are formed by oceanic or fresh water algae are called algal toxins. Algal toxins are released into the waterbodies during bloom, decay and degrade of particular naturally occurring algal species. Algae toxin secretion in small amount does not have any significant effect but during warm seasons when the algae blooms are more intense and of longer duration, consequently, the high concentration of algae toxins will cause algae poisoning. Most poisonings occur among animals when drinking cyanobacteria-infested freshwater, whereas aquatic animals (especially fish, shellfish and shrimp) are also affected as algae is one of their food sources. Although human does not ingest algae, algae poisoning can occur in human upon ingested meat of animals contaminated with algae toxins. This result in food poisoning in human as the algae toxin stored in the animals’ meat are heat resistant and cannot be nullified by cooking or freezing. Algal toxins can cause diarrhea, vomiting, tingling, and paralysis and ultimately lead to death in human who affected with algae poisoning.
In fresh water, the most well-known algae poisoning is caused by blue-green algae. The blue-green algae, also known as cyanobacteria, can produce two types of toxins: microcystins and anatoxins that target the liver and nervous system respectively. Both toxins are delivered to the animal upon drinking from the contaminated water, and in most cases, they are found dead right by the water’s edge. Hence, contaminated ponds and lakes are fenced off and standing water from plant containers, birdbaths, fish ponds, and fountains are removed to prevent livestock from drinking in these contaminated water source.
In marine water, the algae toxins are composed of okadaic acid, saxitoxins, brevetoxins, domoic acid, azaspiracids, pinnatoxins, yessotoxins, pectenotoxins and cyclic imines. Take shellfish for example, the poisoning symptoms post-consuming contaminated shellfish can be divided into diarrheic shellfish poisoning (diarrhea, vomit, abdominal pain) due to okadaic acid and paralytic shellfish poisoning (short-term paralysis) caused by saxitoxins. Shellfishes that are intended for consumer are quality controlled at harvest with respect to algal toxins, micro-organisms, heavy metals, organic environmental toxins, and presence of potential toxin producing algae in the sea.
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- WHO. (2018). Natural toxins in food. Retrieved from https://www.who.int/news-room/fact-sheets/detail/natural-toxins-in-food
Prepared by: Chan Yi Wei and Ong Hui Ling
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