Effect of Post-harvesting with Different Photoperiods under Artificial Light Sources on Nitrate and Vitamin C Contents in Hydroponic Green Oak Lettuce

Abstract

Green oak lettuce (Lactuca sativa L.) is a popular vegetable for consumers, but it is concerned about nitrate contamination that may harm human health. However, light can affect nitrate reduction and contribute to the accumulation of vitamin C in vegetables. Therefore, this study focused on the effects of post-harvesting with different photoperiods under artificial light sources on vitamin C and nitrate content in hydroponic green oak lettuce. Green oak lettuces were grown in the NFT system, harvested, and post-harvested under Bulb-LED (Experiment I), Bar-LED (Experiment II), and fluorescent lamp (FL) (Experiment III) for 6, 12, and 24 h photoperiods and replaced the nutrient solution with tap water. The nitrate content was significantly reduced after post-harvesting for 12 h photoperiods under FL (9,012 µg NO3--N/g dry weight) followed by Bulb-LED (13,985 µg NO3--N/g dry weight) and 24 h photoperiods for Bar-LED (10,727 µg NO3--N/g dry weight). Vitamin C content was highest after post-harvesting for 24 h photoperiods under Bar-LED (45.47 µg/ml), followed by Bulb-LED (44.73 µg/ml) and FL (35.40 µg/ml). Post-harvesting with artificial light sources for 12 to 24 h photoperiods can improve hydroponic green oak lettuce quality.