Peptide-Chelated Micronutrients: A New Frontier of Fertilizers for Biofortification of Lettuce

Agronomic biofortification represents an effective strategy to counteract hidden hunger in humans. Salts and synthetic chelates are widely used as foliar or root applications for enriching vegetables with mineral nutrients. Recently, biochelates have been proposed as a sustainable alternative to synthetic chelates, especially peptide-based biochelates that combine the beneficial role of peptides as biostimulants and chelating agents. This study investigated the impact of multiple foliar applications of two peptide-based biochelates for enhancing Fe and Zn in leaves of hydroponically grown lettuce. No significant differences were observed in the fresh and dry weight of lettuce shoots, leaf pigments, leaf antioxidant activity and leaf macronutrient profile, while a significant increase in biochelate treatments was observed in leaf Fe and Zn concentrations in comparison with untreated control (+38.1% and +44.1%, respectively). Leaf concentration of Fe and Zn in biochelate treatments allowed to estimate that 100 g of biofortified fresh lettuce shoots per day in the human diet can contribute to Population Reference Intake from 7.9 to 11.5% for Fe and from 3.3 to 3.9% for Zn. Moreover, Zn-peptide treatments reduced nitrate concentration with respect to control and Fe-peptide (−9% and −11%, respectively), increasing the quality of lettuce leaves. Overall, peptide-based biochelates proved to be a promising, environmentally friendly fertilizer for lettuce biofortification, enhancing Fe and Zn concentration without impairing yield and leaf quality.