Crocus sativus L. Cultivation in Alpine Environments: Stigmas and Tepals as Source of Bioactive Compounds

Saffron is a well-known spice, produced for a long time, mainly in the Mediterranean area. In the last few years, saffron has been seen as an alternative crop for the diversification of agricultural production and a new source of income, due to its high price, including in Alpine areas. Apart from the spice, constituted by the stigmas, saffron production provides a high amount of fresh tepals, which have so far been considered agricultural waste. Recently, studies on the composition of saffron tepals have been revealing their potential as a rich source of bioactive compounds. In this study, we evaluated the productive traits and the quality of the spice of saffron cultivated in open fields in the north western Italian Alps, for 2 years. In addition, in order to valorize the crop residues, we evaluated the bioactive compound content in tepals by using maceration and ultrasound assisted extraction with different rates of water and methanol as solvents. Higher yields in spice were obtained in the second year of cultivation. However, in both years, the spice had a high quality (ISO 3632), and a very high total phenolic content and antioxidant activity. Thirteen bioactive compounds were identified, including flavonols, cinnamic acids, benzoic acids, catechins, and vitamin C, with few differences between sites and year of cultivation. In tepals, the extraction method and the solvent used influenced the evaluated parameters, i.e., total phenolics and total anthocyanins content, antioxidant activity, and the amount of the four phenolic compounds found (hyperoside, rutin, ellagic acid, and epicatechin). Overall, this study revealed that both saffron spice and its by-product, the fresh tepals, produced in the north western Italian Alps can be considered a source of bioactive compounds with nutraceutical properties, having an antioxidant capacity that is often similar or higher than those of some vegetables and fruits.