Effect on the Growth and Nutritional Components in Two Red Lettuces (Lactuca sativa L.) Cultivated Under UV Light in a Mini Plant Factory

Lettuce is one of the most suitable plant species to grow indoor or in a Plant Factory with Artificial lighting (PFAL) system, due to its short height and the relatively low light saturation point. Red lettuces are highly cultivated in PFALs, highly appreciated for its unique pigmentation and antioxidant activity, especially, the anthocyanin content that gives it the red color. However, red lettuces cultivated with PFAL in controlled environments face the challenge of having low anthocyanin content due of the lack of ultraviolet (UV) light that is necessary for its production. In this study, two red-lettuce cultivars ‘Annapolis' and ‘Salanova' were grown in a plant factory with LEDs (light-emitting diode) and UV light treatments to compare their growth trajectory and nutritional characteristics. Other characteristics such as Fresh Weight (FW) and total leaf area were measured to evaluate the influence of UV light in the lettuce growth. The nutritional quality of lettuces was assessed by measuring anthocyanins and polyphenols contents using a microplate reader and their ascorbic acid content measured via a reflectometer. Fresh Weight (FW), leaf area and leaf thickness under the conditions of this study, showed no effect (p>0.05) on the plants growth with the incorporation of UV radiation. However, the incorporation of UV light increased the functional components in ‘Annapolis' and ‘Salanova' lettuces. The polyphenol and anthocyanins contents in both lettuce cultivars showed significant differences (p<0.05). For ascorbic acid content, a significant difference was found only for ‘Annapolis' lettuce. The incorporation of UV light can increase the functional ingredients such as polyphenols and anthocyanins without growth suppression for ‘Salanova' cultivar. UV light increased polyphenol and anthocyanins contents in both cultivars, making them suitable cultivars for PFAL under the growth conditions used in this experiment. These results taken together can be used to improve the accumulation of functional ingredients in red lettuces without growth suppression incorporating UV light and that could be suitable for production in PFALs.