Enrichment of Vigna unguiculata (L.) Walp sprouts with iron and zinc: influence on antioxidant capacity and phytochemicals

Micronutrients are essential for the growth and development of animals, plants, and humans. Crop biofortification has emerged as a viable strategy to address iron (Fe) and zinc (Zn) deficiencies in the soil. Biofortification with Fe and Zn during seed germination is particularly valuable, as it not only meets nutritional requirements but also helps prevent diseases associated with Fe and Zn deficiencies. This study aimed to evaluate the antioxidant capacity and phytochemical content of cowpea sprouts (Vigna unguiculata L.) biofortified with Fe and Zn. Cowpea shoots were cultivated in a growth chamber under dark conditions with controlled temperature and water supply, and four concentrations of iron and zinc (0-, 5-, 10-, and 15-mM L⁻¹) were applied. The results indicated that optimizing the Fe and Zn concentrations was necessary to enhance the antioxidant capacity in the sprouts while avoiding stress from excessive nutrient levels. The low Zn concentration (5 mM) in the absence of Fe proved most effective in increasing antioxidant capacity, reaching 196.18 µg mL⁻¹. Zn application alone or at reduced Fe concentrations promoted a higher phenolic content in the sprouts. Additionally, the combination of 5 mM Fe with 15 mM Zn resulted in the highest condensed tannin content (102.67 mg catechin g⁻¹), whereas the combination of 15 mM Fe with 0 mM Zn produced the lowest phytic acid level at 0.32 mg FA g⁻¹.