Combined effects of cations in fertilizer solution on antioxidant content in red lettuce ( Lactuca sativa L.)

Abstract BACKGROUND Red lettuce is consumed worldwide because it is a great source of natural antioxidants. To design a fertilizer formula to boost its nutritional value, this research simultaneously studied the effects of significant cations among the macronutrients for plant growth (K, Mg and Ca) and the effects of the electrical conductivity (EC) of the nutrient solution on phenolic compound production and mass productivity of hydroponically grown red lettuce. RESULTS Red lettuce grown under the control treatment provided the highest mass productivity (under low‐stress conditions). The highest antioxidant content, measured as milligrams of phenolic compounds per gram dry weight (at a high‐stress condition) via both Folin–Ciocalteu and HPLC analyses, was observed in growth media containing 100 ppmK : 20 ppm Mg : 70 ppm Ca (with EC equal to 1241 μS cm−1). It was found that EC within the range of this examination had no significant effect on the mass productivity or on phenolic compound productivity. The phenolic compound productivity, defined as the amount of phenolic compounds produced per unit of planting area per unit of time, was optimized with the optimum formula for maximum phenolic compound productivity of 90 ppm K : 29 ppm Mg : 77 ppm Ca, or a corresponding EC of 1307 μS cm−1. CONCLUSIONS The study demonstrates that health‐promoting nutrient production in red lettuce could be stimulated in a practical manner by adjusting the cation concentrations in fertilizer solution. © 2021 Society of Chemical Industry