Terpenoids (extraction, quantification, and biological activities)

Terpenes comprise a wide range of compounds with different physicochemical properties. They are classified into different groups, i.e., monoterpenes, sesquiterpenes, diterpenes, sesterpenes, triterpenes and tetraterpenes (carotenoids), depending on the number of isoprene units present in the structure. Their isolation from plants requires the use of specific techniques depending on the properties of the compounds. Conventional methods mainly include distillation for volatile and semivolatile terpenoids (with the production of essential oils) and solvent extraction. More environmental sustainable techniques have also been developed such as headspace sampling for volatile terpenes, supercritical fluid extraction or extraction with green solvents. Quantification of terpenes is deeply discussed since it can be quite complex and time-consuming, especially when the volatile fraction is involved. The biological activities of terpenes and terpenoids are also described, with particular attention to essential oils and to the traditional uses in Europe of plants, which mainly contain this class of compounds.