Iodine biofortification of sweet basil and lettuce grown in two hydroponic systems

Two hydroponic techniques (floating system and aeroponics) were assessed for iodine (I) biofortification of sweet basil (Ocimum basilicum L.) and baby-leaf lettuce (Lactuca sativa L.). Iodine was supplemented by adding KI into the nutrient solution to achieve a final I concentration of 10 μM. Shoot biomass production and leaf concentration of I, nitrates, total phenols and pigments were measured on the occasion of two successive cuts, 14 and 28 days after transplanting. In both the hydroponic systems, the supplementation of KI represented an effective method for the biofortification of basil as it did not affect the plant growth, while it moderately reduced the biomass production in lettuce. Leaf I accumulation occurred to a greater extent in aeroponics than the floating system in both species. In KI-treated basil plants, leaf I content ranged between 9.76 and 23.58 mg kg− 1 FW. Consequently, 6 g of fresh basil leaves, which is contained in a portion of Italian pesto sauce (12 g), could satisfy 40%–94% of the Recommended Daily Intake (RDI) of iodine for healthy adults (150 μg day− 1). In lettuce, leaf I contents of first-cut leaves were 1.55 and 3.60 mg kg− 1 FW, in the floating system and aeroponics, respectively. Therefore, a serving size of 26 g of lettuce containing I from 1.55 (floating culture) to 3.60 (aeroponics) mg kg− 1 FW could satisfy 27 % to 62 % of the RDI of iodine. Lettuce grew much less in the floating system than aeroponics, probably because of the lower dissolved oxygen level in the nutrient solution as compared to aeroponics. Basil was less sensitive to the oxygen availability in the root zone, since no differences were detected between the two hydroponic systems in terms of fresh and dry biomass.