Zn deficiency is considered as a major risk factor for human health. Here, the effects of Zn biofortification, a complementary solution for mineral malnutrition, were examined in two leafy vegetables, Lactuca sativa and Brassica oleracea in order to select Zn-efficient plants. Zn supply did not affect the biomass, but the concentration of malondialdehyde increased in both plants. Zn-use efficiency increased with respect to Zn concentration, total Zn accumulation (TZnA), and Zn utilization efficiency (ZnUtE). Nevertheless, Zn-use efficiency in L. sativa was lower than in B. oleracea. L. sativa showed lower levels of phenolic compounds, and reduced ascorbate, reduced glutathione and γ-aminobutyric acid than in B. oleracea. Furthermore, both plants had higher concentrations of Ca, Mg, Fe, and Mn, especially 20 µM Zn in L. sativa and 10-20 µM in B. oleracea. Our results indicate that the application of 20 µM Zn in L. sativa and 20-80 µM Zn in B. oleracea promoted the Zn accumulation and improved the leaf essential-nutrient quality for human health. Nevertheless, in B. oleracea higher Zn concentration, TZnA, phenolics, antioxidants and nutrient concentrations were observed. B. oleracea is emerging as a better choice and more efficient candidate in Zn-biofortification programs. The best approach to increase human Zn levels is to encourage greater consumption of both green leafy vegetables, especially B. oleracea.
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