Increasing the functional quality of Crocus sativus L. by-product (tepals) by controlling spectral composition

Crocus sativus L. is a crop grown for spice production, and large amounts of residues from the flowers are produced during the process. The underutilized by-product from saffron spice production, the C. sativus tepals, was investigated as a promising raw material of natural bioactive compounds using light spectrum manipulation in controlled environments. The plants were grown under either light-emitting diodes (LEDs) or natural light (NL, greenhouse). LED experiments were performed in controlled-environment chambers (120 µmol m–2 s–1of photosynthetically active radiation, 18 °C, 16-h photoperiod). The LED treatments used were as follows: (i) red ʎ = 660 nm (62%) and blue ʎ = 450 nm (38%) (RB); and (ii) red ʎ = 660 nm (50%), green ʎ = 500–600 nm (12%), and blue ʎ = 4 50 nm (38%) (RGB). Flower growth parameters, total phenols, total flavonoids, flavonols, flavonol glycosides, and antioxidant properties were measured in harvested tepals. Floral by-products from plants grown under the two LED treatments accumulated higher amounts of antioxidant compounds compared to those of plants grown under NL. The total flavonoids content was significantly enhanced in the RGB LED treatment, while the corolla fresh weight significantly declined in the same treatments. The higher content of bioactive secondary metabolites in plants grown under both RB and RGB light environments resulted in increased antioxidant capacity measured by DPPH free-radical scavenging capacity and the ferric reducing antioxidant power method. These results indicate that manipulation of LED spectra could boost secondary metabolites and antioxidant capacity to obtain phytochemically enriched floral by-products with superior functional quality.