Short-term postharvest UV-A and UV-B application enhances bioactive plant secondary metabolites in leafy vegetables

Abstract

UV light is an important stimulator for bioactive secondary plant metabolites. Short-term postharvest applications are thought to enhance their concentration. Postharvest treatments with PAR light (control), UV-B (310 nm for 0.5 h, to 2 h), and two UV-A wavelengths (340 nm and 365 nm for 1.5 h, to 6 h) were applied to baby leaves of lettuce and chicory. Short-term UV-B (0.5 h and 1 h) and UV-A (1.5 h and 2 h) treatments achieved the highest accumulation of phenolic acids e.g. chicoric acid and sesquiterpene lactones e.g. 11(S),13-dihydro-8-deoxylactucin, in both lettuce and chicory. In chicory, chlorogenic acid levels increased with prolonged UV-A radiation. In addition, flavonoid glycosides were induced by both UV-B and UV-A light in chicory. These changes were accompanied by enhanced antioxidant activity after short-term postharvest UV treatments. UV-B (1 h) and UV-A (2 h) resulted in the highest levels of lutein and β-carotene in both lettuce and chicory. These findings underscore that short-term UV-B and UV-A treatments effectively modulate the concentration of bioactive compounds. Changes in sesquiterpene lactone concentrations may also have an impact on taste and consumer acceptance. Postharvest UV treatment can be applied as more cost effective and reliable than preharvest treatments, making them a real opportunity for commercial applications.