Effects of UVB Light, Wounding Stress, and Storage Time on the Accumulation of Betalains, Phenolic Compounds, and Ascorbic Acid in Red Prickly Pear (Opuntia ficus-indica cv. Rojo Vigor)

Prickly pear (Opuntia ficus-indica cv. Rojo Vigor) fruit is an excellent source of secondary metabolites with health-promoting properties (i.e., betalains, flavonoids, and ascorbic acid), and thus, it is relevant to find postharvest treatments that increase their concentration. Postharvest abiotic stresses such as wounding and ultraviolet radiation can induce the accumulation of secondary metabolites in different horticultural crops. In the present study, the effect of ultraviolet B (UVB) radiation applied alone or combined with wounding stress on the accumulation of betalains, phenolics, and ascorbic acid in red prickly pear was evaluated. Whole and wounded fruit samples were treated with UVB radiation (6.4Wm(-2)) for 0, 15, 90, and 180min and stored for 24h at 16 degrees C. The content of bioactive compounds was evaluated before and after storage. The application of UVB radiation for 15min was the most adequate treatment to induce the accumulation of bioactive compounds. In this context, UVB radiation (15min) of the wounded tissue resulted on an immediate accumulation of betalains (33-40%) and ascorbic acid (54-58%) in the pulp and peel of the fruit. Likewise, after storage, the pulp of irradiated whole fruits showed the highest accumulation of phenolics (125.8%) and betalains (49.8%) as compared with the control, whereas the stored wounded tissue treated with UVB presented accumulation of ascorbic acid in the pulp (67.2%) and peel (84.6%). The stressed tissue with enhanced concentration of nutraceuticals could be transformed into functional processed foods or used as raw material for the extraction of compounds with applications in health-related markets.