Effect of Supplementary Pre-Harvest LED Lighting on the Antioxidant Properties of Lettuce Cultivars

Supplementary solid-state lighting was applied within an industrial greenhouse for pre-harvest treatment of lettuce cultivars (Lactuca sativa L.). Lettuce was grown under natural solar illumination (7 h photoperiod) with the photoperiod extended by 12 h using high pressure sodium lamps (photosynthetic photon flux density of 130 mu mol m(-2) s(-1)). The additional flux (170 mu mol m(-2) s(-1)) generated by red 638-nm light emitting diodes was applied for 3 days before harvesting during the photoperiod extension. Such a pre-harvest treatment was found to remarkably enhance antioxidant properties of lettuce. In particular, an increased content of alpha-carotene and phenolic compounds (by up to 2.8 and 1.8 times, respectively) as well as enhanced free radical scavenging activity (by up to 2.4 times) were revealed due to the increased activity of the metabolic system for the protection from a mild photo-oxidative stress. The observed effect of supplementary red light appeared to be more distinct for green leaf type lettuce cultivars that have relatively lower antioxidant ability in comparison with red leaf type cultivars.