Regulation of Plant-Based Biofortification in Mmicrogreens of Sunflower (Helianthus annuus L.) and Water Spinach (Ipomoea aquatica Forssk.) Using Exogenous Iron Application

The objective of this study was to investigate the potential impact of exogenous iron (Fe) supplementation on the Fe concentration and health-promoting properties of sunflower and water spinach microgreens.

Seven-day-old sunflower and water spinach seedlings were grown in a plant growth incubator (25°C ambient temperature, 65 ± 5% relative humidity, 12 h d⁻¹ photoperiod with 150 µmol m⁻² s⁻¹ photosynthetic photon flux density). These were directly exposed to different concentrations of FeSO₄ (0, 0.1, 0.2, and 0.3 mM Fe) in the culture solution for eight days prior to microgreen harvesting.

The total Fe content of sunflower microgreens treated with 0.2 mM Fe increased significantly by 3.01-fold compared to the control. Interestingly, 0.3 mM Fe treatment significantly reduced α-tocopherol and total tocopherol concentrations in microgreens by 23% and 61% compared to the control. Further, Fe treatment significantly reduced calcium and potassium levels. The water spinach microgreens exposed to 0.3 mM Fe application had a maximum Fe concentration of 144 µg g⁻¹ DW, which was 3.87 times greater than the control, resulting in chlorophyll pigment impairment, total carotenoids degradation, and tocopherol reduction. In addition, the 0.2 mM Fe treatment resulted in a maximum ascorbic acid content of 21.7 mg g⁻¹ DW.

The optimal increase in total Fe levels (48 µg g⁻¹ DW) in sunflower microgreens was attained with a 0.1 mM Fe exogenous application, which was lower than that in water spinach microgreens (by ~ 2 folds). Ascorbic acid and tocopherol concentrations in the water spinach microgreen peaked at 0.2 mM Fe, but they dropped under high Fe treatment. Water spinach microgreens treated with 0.1–0.2 mM Fe were found to be an excellent protocol for Fe biofortification in large-scale production, offering fresh biomass, a high Fe content, and health-promoting properties.