Phytochemical is a very broad term used to describe chemicals produced by plants which have a biological effect on other organisms. They are arranged into different categories based on their chemical properties rather than their actions. Examples of categories include: flavanoids, alkaloids, terpenes, and carotenes.
The unmistakable hot flavour of chili peppers it will literally bind to cellular receptors for pain and heat in mammals. Birds lack this however and can consume chilies without any ill effects. Peppers have evolved to have its seed dispersed by birds while deterring grazing mammals which will grind up the seed with their teeth.
Humans have developed a taste for capsaicin as it has mild narcotic effects making the person jittery and effecting the skin making it flushed and sweaty. It has some medicinal effects as a mild pain reliever for aliments such as arthritis, it might also be a fat burner.
Closely related chemically to Vitamin A, it cannot substitute be a substitute for it like beta-carotene can. It's a bright red pigment and is found in tomatoes, pumpkin, papayas, apricots, pink grapefruit, and watermelon. Its function in plants is as a photosynthetic pigment, meaning that it can convert light energy into carbohydrates but to a lesser degree than chlorophyll. It also functions to advertise to animals when fruit is ripe in order to aid in seed dispersal.
While not an essential nutrient like Vitamin A it is known for its strong antioxidant properties and there is some evidence for lowering blood lipids and blood pressure.
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Carotenes are fat soluble meaning that it is very easy for the body to store them for long periods of time. Arctic mammals such as polar bears and seals store Vitamin A in their livers at such concentrations as to be potentially toxic if they are consumed by humans. The livers have been traditionally discarded by indigenous peoples in order to avoid poisoning.
While it's true that plants don't have cholesterol they produce very similar chemicals called polysterols and beta-sitosterol is an example of one of these. Their function is the same as cholesterol in animals, as a component of cell membranes. However it also a role to play in response to stress such as temperature and insect attack.
Beta-sitosterol is widely distributed in the plant world but is mostly consumed by humans with nuts, vegetable oils, and avocados. While lower amounts may decrease cholesterol levels, but having too much in a diet can increase the severity of heart attacks.
There are a larger number of tannins but tannic acid is the best known, its name being taken from the fact that tannins been traditionally been used to preserve leather.
Tanninic acid is consumed in food and is known for astringent properties, which means it will make the mouth feel dry and puckers it slightly and are most notably in unripe fruits. Some varieties of fruit such as crabapples and chokecherries have high levels regardless of ripeness.
Tannins as a whole will react with protein causing it to fall out (precipitate) and so are used as a defense against insects. They are stored inside of cells as they could potentially be toxic to the plant but are released upon the death of the cell.
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Wines, certain types of beer such as Flanders Red, and spirits have traditionally been aged in oak barrels. Oak has a high amounts of tannins and will help to neutralize some of the off-flavours as well as add more complexity. In addition they give colour to whiskies, brandies, and some types of rums and tequilas. Too short of time aging in oak will result in too strong of "woody" flavour but these mellow over time which is why ageing is considered to be desirable. Oak also contains the closely related vanillin, and this flavour will likely come through with aging.
It is a complex carbohydrate which primarily functions in binding cell walls together, but might also have a role to play in repairing damaged DNA.
It is primarily used by humans as a thickening agent, most notably in jams and jellies. In digestion it traps carbohydrates preventing absorption and is considered a source of soluble fiber. There is also some evidence that it might be useful in treating people exposed to certain radioactive materials, helping them rid their bodies of them.
Pectin also has an important role in fruit ripening. As the fruit develops it contains higher proportions of pectin and once ripening is triggered an enzyme breaks it down making the fruit more soft.
Found in mustards, horseradish, wasabi, and radish. Relatively benign on its own it will break down into allyl isothiocyanate when the plant is damaged due to an enzymatic reaction. Allyl isothiocyanate is responsible for the characteristic hot spicy flavour of these plants and helps to deter grazing animals and to a lesser degree as a defense against insects and disease.
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Wasabi is very difficult to grow. It grows in dry riverbeds out of direct light in temperatures of 8 to 20 degrees Celsius. Because of this it is very expensive and especially in western countries horseradish which has been dyed green is usually used instead.
This is a phosphorus storage system in plants, especially in seeds where it provides the nutrient to the next generation. Phytic acid is not digestible under normal conditions but breaks down if the seed is sprouted or fermented which frees up the phosphate. The downside to phytic acid is that it binds to minerals such as iron and zinc which prevents their absorption.
A type of flavanoid found in milk thistle seeds. It has hormonal properties in plants being involved in the chemical response to attack from pests.
It is quite useful in treating liver damage due to poisonings, especially from mushroom toxins and cirrhosis caused by alcohol. There is also ongoing research in cancer treatments.
On it's own silibinin has poor solubility which has lead to other synthetic molecules very similar being developed but with better solubility. This has lead to a ten fold increase in biological activity over silibinin.
A plant pigment in the flavanoid class which acts as a transportation vessel for hormones between cells in the plant. It is found in small quantities in a very wide variety of plants and will inhibit proteins in humans and animals. In addition it also has estrogen like properties. Despite significant biological activity and claims by the natural health industry, there is doesn't seem to be any evidence of being beneficial.