Iron Biofortification of Red and Green Pigmented Lettuce in Closed Soilless Cultivation Impacts Crop Performance and Modulates Mineral and Bioactive Composition

Consumer demand for vegetables of fortified mineral and bioactive content is on the rise, driven by the growing interest of society in fresh products of premium nutritional and functional quality. Biofortification of leafy vegetables with essential micronutrients such as iron (Fe) is an efficient means to address the human micronutrient deficiency known as hidden hunger. Morphometric analysis, lipophilic and hydrophilic antioxidant capacities of green and red butterhead lettuce cultivars in response to Fe concentration in the nutrient solution (0.015 control, 0.5, 1.0 or 2.0 mM Fe) were assessed. The experiment was carried out in a controlled-environment growth chamber using a closed soilless system (nutrient film technique). The percentage of yield reduction in comparison to the control treatment was 5.7%, 13.5% and 25.3% at 0.5, 1.0 and 2.0 mM Fe, respectively. Irrespective of the cultivar, the addition of 1.0 mM or 2.0 mM Fe in the nutrient solution induced an increase in the Fe concentration of lettuce leaves by 20.5% and 53.7%, respectively. No significant effects of Fe application on phenolic acids and carotenoid profiles were observed in green Salanova. Increasing Fe concentration in the nutrient solution to 0.5 mM triggered a spike in chlorogenic acid and total phenolics in red Salanova lettuce by 110.1% and 29.1% compared with the control treatment, respectively: moreover, higher accumulation of caffeoyl meso tartaric phenolic acid by 31.4% at 1.0 mM Fe and of carotenoids violaxanthin, neoxanthin and &beta:-carotene by 37.0% at 2.0 mM Fe were also observed in red Salanova compared with the control (0.015 mM Fe) treatment. Red Salanova exhibited higher yield, P and K contents, ascorbic acid, phenolic acids and carotenoid compounds than green Salanova. The wok shows how nutrient solution management in soilless culture could serve as effective cultural practices for producing Fe-enriched lettuce of premium quality, notwithstanding cultivar selection being a critical underlying factor for obtaining high quality products.