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Plants and animals generally produce toxins naturally as defense mechanisms to protect them from environmental stresses and predators. Plant products or animals with a higher amount of toxins are not used as food. For an instance, though castor seeds contain high amount of fat, but it is not used as a food as it contains a toxin called as Ricin. However, there can be chemicals that can cause various abnormal conditions to humans in minute quantities. These harmful chemicals can be categorized as mutagens, teratogens, antinutrients, carcinogens, physiological irritants. These chemicals can cause negative impacts on health in long term ingestion. Effects from these chemicals can be enhanced when ingested by people with metabolic errors which are genetically inherited and when large quantities are ingested.

Lactose is a disaccharide present in milk that is known as the milk sugar. Some people who have difficulties in digesting lactose develop lactose intolerance which results from breaking down of lactose by intestinal micro flora producing acid and gas. Lactose free milk is commercially available to such people. Fructose intolerance results from incapability to digest fructose which is less common to lactose intolerance. People with Celiac disease cannot digest gluten which is a major constituent in wheat. Gluten causes internal hemorrhages producing bloody stools. Galactocemia, Phenylketonuria, Hemochromatosis, Wilson’s disease are some other diseases results in metabolism errors.

Food allergy is an immunological response caused when a foreign body is entered into the body and the immune system produce antibodies. In this situation, body recognizes the food constituent as a foreign body. Major allergenic food groups include milk, wheat, nuts, egg, meat/fish/shellfish, soy and peanuts. Prominently, the proteins in these foods are responsible for allergic reactions.

Protease inhibitors are a common type of plant toxins which are rich in legumes and cereals. By inhibiting these enzymes, these toxins make the specific proteins less available. Most of these protease inhibitors are heat labile. In contrast, some of these enzyme inhibitors are known to suppress tumor growth. Hemagglutinins and lectins present in high amounts in legumes and grains. Lectins are known to promote blood clotting, damage gut epithelium leading to local hemorrhages and kidney damage. Lectins also possess anticarcinogenic properties. Saponins found in soybean, spinach are another toxin with hemolytic effect. Vicine and covicine present in fava beans lead to a condition called favism which is developed in oversensitive people. This oversensitivity hereditary and controlled by a sex linked gene commonly occurs in Afro-Americans, Africans. Skeletal abnormalities results from altered metabolism in connective tissue due to Lathyrogens present in sweet pea, which are chemically unusual amino acids. Glucosinolates found in vegetables of Cruciferacea family promotes hypo and hyper thyroidism conditions.

Cyanogenic glucosides are another group of toxins which yields Hydrogen cyanide upon exposure to gastric acids and plant enzymes. Hydrogen cyanide is a potent respiratory inhibitor and arrests the cellular respiration very efficiently. Cyanogenic glucosides are commonly found in sorghum, almonds, cassava, lima beans, peach seeds etc. This is a major problem in countries where cassava is the staple food. Cyanide can potentially destroy the β cells of pancreas. Bitter varieties of cassava contain higher amount of these toxins.

Phytic acid is a naturally present metal binder which reduces the availability of metal ions. Phytic acid is a simple sugar with many phosphate groups attached. These phosphate groups can bind to multivalent cations. When metal ions are bound with phytates, they become unavailable. Phytic acid is present in wheat. In countries that consume wheat in large quantities, fertility of males is reduced as Zink ions are made unavailable.

Germinating potatoes contain eyes with greenish areas which contain certain amount of solarine. Solarine is a carcinogen. Mushrooms are well known for food intoxications. Mushrooms like Amanita contains deadly toxins called Amanita toxins.

Apart from plant toxins, fish toxins are important. Paralytic shellfish poisoning results from a toxin produced by dinoflagellates belongs to Saxitoxins. This is a heat stable neurotoxin which blocks the entry of Sodium ions into nerve cells. Diarrheal shellfish poisoning is commonly seen in Europe, Latin America and Japan developed as a result of Okadaic acid from dinoflagellates. Ciguatera toxicity is most injurious from public health and economic stand point. The toxicity is due to toxins produced by a marine algae; Gambierdiscus toxicus. This fat soluble toxin is heat stable and causes paralysis and death.

These naturally present toxins are difficult to eliminate. It is important to destroy the possible toxins by using proper cooking methods.
These type of toxins even enter food chain by various methods. Research in this field are producing such devices to identify the microorganims or their toxins to prevent them from entering in food chain. Many outbreaks of deadly diseases can now be predicted with the help of newly developed methods. These methods employ geospatial algorithms, food borne pathogen ecology and GIS which stands for Geographic Information System. This combined information predicts the hot spots where these deadly pathogens are present and thus can identify the source of contamination. This identification helps in control of linked contamination on the farms and in various geographical areas. These methods also uses tree tools with sensed data, like soil type, topography, environmental trends and proximity to water and forests which helps in prediction of pathogens presence.
While performing such research, scientist could look at data and can tell farmer the place or hotspots where these food borne pathogens could be present. This research came to such conclusions on the basis of intensive data collection, analysis and arriving at a point. The researcher collected around 600 samples of water, soil, feces and swabs from various farms and environment.
With developments, these types of tool can be used to provide completely new approach which is based on scientific facts on how to protect or reduce likelihood of contamination with bacteria and other microorganisms. Once these hotspots are identified, farmers may prevent the spread of such bacteria by practicing methods like draining standing water, reducing and adjusting livestock graze etc.,
The detail of this research and new method of identification of places of deadly pathogens is published in journal "Applied and Environmental Microbiology" by its leading author Laura Strawn.
Natural toxins in food

Food that we eat contains more toxins than we can imagine. Naturally occurring toxins are produced by various plants species as a response to stressful environmental conditions, such as drought, low or high temperature, insects… These toxins belong to different chemical classes (amines, glycoalkaloids, glycosides…), but their final effect on human health is always more or less harmful.

Here are few more examples of naturally occurring toxins in plants:

Seeds from apples and pears and kernels from apricot and peach contain substance called amygdalin. This substance can release hydrogen cyanide and induce illness or even death if ingested in higher dose. Concentration of amygdaline may vary from kernel to kernel, and although kernels from apricot can be purchased normally in most healthy food stores, maximal dose should be 4 kernels per day. Apple and pear seeds will not induce damage if ingested accidentally, but you should avoid eating them whenever possible.

Kumara is a member of sweet potato family. This vegetable produces toxin, known as ipomeamarone when plant is injured, attacked by insects or when exposed to stressful environmental conditions. Cattle poisoning associated with poisonous kumara have been recorded and experts advice to remove all injured and potentially dangerous parts of kumara when preparing the vegetable for cooking. If kumara taste bitter - it probably contains ipomeamarone and you should not eat it.

Parnish release toxins known as furocoumarins when exposed to harsh weather conditions. Since highest concentration of toxins is found in peel and surface layer, plant should be peeled and all damaged parts should be removed before cooking. Side effects associated with furocoumarins poisoning are stomach ache and painful skin reaction if person is exposed to increased amount of UV light during consumption of the poisonous plant. Level of toxins will drop during cooking, boiling or preparing the plant in the microwave. Cooking water should be thrown away.

Potatoes produce glycoalkaloids as a defense mechanism against microorganisms, UV light and injury. These chemicals give potato a bitter taste, which is the easiest way to identify uneatable potato. Depending on the geographic area and part of the plant you are eating, amount of glycoalkaloids may cause more or less damage. Stomach ache will be immediate reaction to glycoalkaloids in food. In the case that large amount of poisonous potatoes is ingested, death may occur. Since glycoalkaloids do not get destroyed during cooking, potatoes should be carefully cleaned and peeled, including removal of all sprout, damaged and green parts of the plant.

Many beans contain lectins. Red kidney beans contain especially high concentration of these toxins. When ingested raw, kidney beans can induce vomiting, diarrhea and stomach ache. They need to be prepared and cooked properly in order to destroy toxin. First, beans should be soaked in water for 5 hours and then it should be cooked at least 10 minutes at high temperature. Low cooking temperature can't destroy toxin and it can induce even bigger damage than toxin in the raw form.

Rhubarb contains oxalic acid. Highest levels of oxalic acid are located in the plant’s leaves and they should not be eaten. Concentration of oxalic acid depends on the soil, geographic area and maturity of plant. In case you eat plant with too much oxalic acid, you may experience muscle twitching and cramping, respiratory difficulties, bradicardia, pain, vomiting, convulsion and even coma.

Zucchini may contain toxins known as cucurbitacins. These toxins are often seen in wild plants and rarely in commercially available vegetable. Since toxins give zucchini a bitter taste, you can detect uneatable vegetable by taste and strong odor. Cucurbitacins can induce vomiting, stomach cramps and diarrhea.
Cassava and bamboo sticks are inevitable part of Asian cuisine. Both species contains well known poison - hydrogen cyanide. Toxin can be removed if plants are properly treated before eating: cassava should be peeled and sliced and bamboo should be peeled, and leaves and fibrous tissue (located at the base of the stick) should be removed before boiling, baking or roasting the plants.

Honey made of bees that collect nectar from the tutu plants can be poisonous. This plant is native to the New Zealand. Cases of honey intoxication are rare, but they have been recorded in the past.

When you look at the list, it seems that everything we eat is poisonous and dangerous for our health. Reality is actually quite different. Regular fruits and vegetable meals are essential for our well being and most toxins can be avoided if plants are treated and prepared properly before consumption.
wow you write is very well. Actually I never know about this that we have many toxins in our food.. But I think you have a good stuff about food toxins.. Anyhow thanks for sharing this wonderful information and please keep sharing.