Saffron (Crocus Sativus L.) apocarotenoids: A review of their biomolecular features and biological activity perspectives

Carotenoids are a class of more than 600 secondary metabolites occurring in plants, algae, and photosynthetic bacteria; their flat, long C40 system of alternating double and single bonds allow them to be the sources of the yellow, orange, and red colours of many plants, including fruit and vegetables, where they are believed to contribute to the overall photosynthetic processes. They are important in human nutrition as a source of vitamin A, and act as preventive agents against cancer and heart disease. Furthermore, they are important precursors of several compounds responsible for the flavour and fragrance of foods and flowers. Carotenoids are also the most characteristic and important components of saffron (Crocus sativus L.) stigmas, directly responsible for the particular colorant features of this spice, as well as precursors of compounds responsible for its bitter taste and aroma. Saffron carotenoids include fat-soluble components such as licopene, β-carotene and zeaxanthin, but also and mainly, a peculiar class of molecules, the C20 apo-carotenoid crocetin (8,8’-diapo-8,8’-carotenedioic acid) and its ester derivatives, with one or more sugar moieties, which lend these compounds the peculiar characteristic to be the sole water-soluble components among the carotenoids – the trans-crocetin (β-d-digentibiosyl) ester being the most important and abundant component of this class. Crocetin and its related compounds have so far been detected only in some Crocus species, in Gardenia jasminoides Ellis, Artocarpus hetrophyllus Lam. (jackfruit), Coleus forskolii (Willd.) Briq., Jacquinia angustifolia L., Buddleja officinalis Maxim., and Nyctanthes arbortristis L. (night flowering jasmine). The peculiar chemical structure of saffron apocarotenoids gives them particular characteristics in terms of chemical/physical reactivity and solubility; furthermore, this pool of metabolites are apparently responsible for the biological properties ascribed to this spice so far: antioxidant, antitumor and memory effects enhancer, to list some of them. A detailed review on this particular and unique class of carotenoids will be given, together with some biosynthetic discussion and the latest scientific discoveries on their biological activities.