Growing spinach (Spinacia oleracea) with different seawater concentrations: Effects on fresh, boiled and steamed leaves

Agriculture is the human activity requiring the higher amount of freshwater. Nevertheless, water availability is already an issue in many regions of the world, suggesting the need of alternative water sources to face the increasing food demand. Spinacia oleracea plants have been cultivated in a floating hydroponic system where nutrient solution was integrated with 10% and 20% of seawater. Plant growth was monitored during the experiment together with morphological adaptations at the shoot level. At the end of the crop cycle, leaves were collected and processed with the two most common cooking processes such as boiling and steaming. Raw, boiled and steamed leaves were then analyzed to determine their sodium and potassium concentrations, the total phenolic content and the nitrates concentration. Our results showed that the use of seawater in the hydroponic spinach cultivation determined positive effects on growth parameters, with an increased relative growth rate assessed for both seawater treatments compared to the control. Leaves morphological adaptations were assessed only in 20% seawater treated plants (i.e. reduced leaf water content, leaf area and specific leaf area; increased specific leaf weight and leaf succulence), whereas the moderate seawater treatment did not lead to any difference compared to the control. Seawater treatments significantly increased sodium content in leaves, which could be consumed without adding any salt. Potassium was not affected by salinity treatments, whereas both total phenolic content and nitrates decreased accordingly with increasing salinity Concerning the cooking processes, steaming proved to be a better cooking method compared to boiling with the aim of preserving the nutritional values of spinach leaves. In conclusion, our results suggest that the use of a certain level of seawater in the spinach cultivation is a practical possibility to be explored in the direction of saving freshwater and increasing crop production enhancing the quality and taste of vegetables.