Biological relevance of terpenoids. Overview focusing on mono-, di- and tetraterpenes.

The role of fruit and vegetables in human nutrition and public health are taken into account in most nutritional recommendations. Fruit and vegetables contain an abundance of phenolic substances, terpenoids and other natural antioxidants that have been associated with protection from and treatment of chronic diseases such as heart disease or cancer. Terpenoids are a group of substances which occur in nearly every natural food. Their main subclasses discussed as beneficial to maintain and improve health are monoterpenes (like limonene, carvone or carveol), diterpenes (including the retinoids), and tetraterpenes (which include all different carotenoids like alpha- and beta-carotene, lutein, lycopene, zeaxanthine and cryptoxanthine). To be discussed as health promoting or biofunctional, the significant impact of a substance either on human metabolism or on well-defined and appropriate biomarkers must be shown. Based on the latter point, this paper reviews the literature on mono-, di- and tetraterpenes, with special focus on their impact on human health to answer the question of their biofunctionality. Special emphasis will be placed on their different mode of action, e.g. to affect oxidative stress, carcinogenesis and cardiovascular diseases.