Modifying folate and polyphenol concentrations in Lamb's lettuce by the use of LED supplemental lighting during cultivation in greenhouses

The effect of light-emitting diode (LED) supplemental lighting on the folate and polyphenols content as well as antioxidant properties of Valerianella locusta (Lamb's lettuce) cultivated in greenhouse in autumn and winter seasons was evaluated. Six LED-lightning combinations were used. Four of them differed in percentage share of red (R) and blue (B) in emission spectrum: 100%R, 90%R/10%B, 70%R/30%B, 50%R/50%B. The next two combinations emitted either warm (4700K+2700K) or cool (3500K) white light. Control plants were grown under high-pressure sodium (HPS) lamps. High total folate contents, with 5-methyltetrahydrofolate as a dominant form, were detected in plants treated by the supplemental lighting: 90%R/10%B, 70%R/30%B, cool white and warm white in both cultivation seasons. The level of phenolic compounds in tested plants was the highest when treated by 70%R/30%B and cool white light in autumn and all red/blue combinations in winter. Chlorogenic acid was found as the dominating phenolic compound in V. locusta.