Nanoparticles of cerium, iron, and silicon oxides change the metabolism of phenols and flavonoids in butterhead lettuce and sweet pepper seedlings

The aim of the study was to determine the effects of CeO2, Fe2O3, and SiO2 nanoparticles on the metabolism of phenols and flavonoids and the antioxidant status of butterhead lettuce and sweet pepper seedlings. Nanoparticles were used as a 1.5% suspension on the leaves. Phenolic and flavonoid contents increased as well as the antioxidant capacity of sweet pepper after exposure to Fe2O3-NPs. Phenolic and flavonoid concentrations in lettuce were the highest when CeO2-NPs were applied, while glutathione content increased due to Fe2O3-NPs and CeO2-NPs treatment. The highest ascorbic acid concentration was found in sweet pepper exposed to CeO2-NPs. The levels of dehydroascorbic acid, monodehydroascorbate, and L-galactono-1,4-lactone were the highest as a result of foliar spraying of sweet pepper with SiO2-NPs, but the ascorbic acid content in that plant was the lowest. Carotenoids increased after spraying of lettuce with SiO2-NPs. Individual metabolites from phenolic and flavonoid metabolism were determined. In lettuce seedlings, five phenolic compounds were decreased (3,4-diOH-benzaldehyde, ferulic acid, p-coumaric acid, salicylic acid, and vanillin) and two compounds (gallic acid and vanillic acid) were increased in comparison to control plants, while for sweet pepper an increase was observed for four compounds (chlorogenic acid, neochlorogenic acid, ferulic acid, and protocatechuic acid). To the best of our knowledge, this is the first study on the phenolic profile of edible juvenile plants treated with such metal/metalloid nanoparticles. We may also conclude that various nanoparticles may interact differently with phenolic phytochemicals depending also on plant species that have varying levels of stress tolerance.