Exploiting the potential of red orache (Atriplex hortensis var. rubra L.) for the production of microgreens biofortified with selenium or zinc in comparison with Swiss chard (Beta vulgaris ssp. vulgaris var. cicla)

Abstract

The market of microgreens is rapidly growing due to their tenderness and concentrations of many beneficial substances. The range of plant species grown for microgreens production is large and still expanding. Atriplex hortensis var. rubra L. (red orache; RO) is characterised by high vitamin C content and red-purple leaves, and could replace other red-leaved plants in microgreen boxes. The nutraceutical profile of microgreens could be further enhanced by biofortification with essential micronutrients for humans, such as selenium (Se) and zinc (Zn). The aim of our study was to explore the potential of RO for the production of microgreens biofortified with selenium (Se) or zinc (Zn) in comparison with Swiss chard (Beta vulgaris ssp. vulgaris var. cicla; SC), which is a more commonly consumed microgreen. Microgreens were grown in coconut coir irrigated at sowing with water containing different concentrations of sodium selenate (Na₂SeO₄; 0, 1, 3, and 5 mg Se L^-1) or zinc sulphate (ZnSO₄; 0, 2, 6, and 10 mg Zn L^-1). The impact of adding a solution containing different concentrations of Se (0, 1, 3, and 5 mg L^-1 Se) or Zn (0, 2, 6, and 10 mg L^-1 Zn) to the substrate, at the time of sowing, on the growth and nutraceutical characteristics of the microgreens of both species was investigated together with their potential contribution to the daily requirements of Se and Zn for humans. The fresh weight and concentration of pigments, antioxidant compounds, especially ascorbic acid, and nitrate, and the total antioxidant capacity of microgreens were significantly higher in RO than in SC. Treatment with Se or Zn did not significantly affect the yield and quality of SC and RO microgreens, while increasing the microgreen concentration of Se (from 0.57 to 6.96 mg kg^-1 FW) or Zn (from 4.46 to 12.55 mg kg^-1 FW), respectively. Biofortification was more effective with Se than with Zn. A serving dose of 10 g of microgreens biofortified with 5 mg L^-1 of Se could meet the daily requirement of this element in humans. In order to have a significant input (15%) to the daily requirements of Zn from SC and RO microgreens obtained with 10 mg L^-1 Zn, the serving dose should be at least 100 gr.