All plants have the ability to produce substances which confer special effects and these will usually be assigned to various categories such as phenols, alkaloids, fatty acids, terpenes and so on which will then be used to justify claims for particular health benefits So it might be a good idea to look more closely at what some of these are and how and why they are important. Let’s take terpenes, for example.
Names like phenols or terpenes, for example, are name given to different types of chemicals which have something in common. In the case of terpenes, this is related to the way that they are constructed. Essentially they are all built up from the same basic building block just as if you were playing with Lego but only had one particular shaped brick that you could use. In the case of terpenes, this building block is a small unit with five carbon atoms and by joining up two or more of these we can get a variety of more complicated shapes (i.e. molecules). These can give rise to an even larger range of molecules classed as terpenoids which differ only in the way the carbons are bonded to each other or in which oxygen atoms have been added to give alcohols or ketones, for example, and one estimate is that the total number of these compounds is around 50000. The simplest terpenes are the monoterpenes and monoterpenoids which are often highly aromatic and are widely used in the fragrance and perfume industries.
Five common frameworks are shown here. the first one is found in terpenes and terpenoids such as myrcene, geraniol, linalool and citronellal. Myrcene occurs in plants such as cannabis, verbena and hops. Geraniol, linalool and citronellal are found in many flowers and spices. Number 2 is characteristic of terpenes known as pinenes which are the main components of pine resin which is used to make turpentine and also gives retsina its characteristic flavour. Framework #3 occurs in camphor, borneol, which can be extracted from certain trees and also occur in small quantities in herbs such as rosemary. The 4th framework is found in a large number of terpenes and terpenoids, including menthol, which occurs in wild mint and peppermint, limonene, which occurs in manyof tree varieties as well in the peel of citrus fruits, and carvone, found essential oils such as those from dill, caraway or spearmint. Framework 5 is typical of terpenes called carenes which are found in some turpentines as well as in cannabis oil, for example.
While terpenes and terpenoids are widely used for their aromatic characteristics or as solvents, the reason for their wide abundance in nature, and particularly in plants, is that they are essential components of the mechanisms which have evolved for development and survival. They assist communication between plants or of plants with insects, either as deterrents or to attract pollinators. They are also used by the plants themselves to build more complicated compounds such as steroids which are needed for other purposes. Terpenes have often been invoked in the so-called “entourage effect” hypothesis which proposes that they act synergistically to modulate the activity of other active plant substances.