Effect of NaCl concentration and UV-B on lettuce crop in hydroponic system

Abstract

Vegetable consumption has increased in recent years, so it is imperative for the industry to fill expectations in terms of convenience, taste and product quality. Consumers are looking for freshness and soft textures, so baby leaf vegetables are the most promising choice for the development of minimal processing industries. The cultures of baby leaf vegetables have increased due to it fast processing operations and its attractiveness as a gourmet product. Despite these benefits, the short shelf life and fragility are important limitations. In addition, the limited availability of irrigation water and agricultural soils must be optimized. Hydroponics are shown as a valid alternative. This type of culture facilitates the interventions as abiotic stress in order to increase beneficial compounds and prolong postharvest life. The purpose of this study was to compare the separately responses of ‘Lollo Bionda’ lettuce (Lactuca sativa L. ‘Levistro’) grown in hydroponic systems with two different abiotic stresses, increasing NaCl content and exposure to UV-B radiation in order to increase the antioxidant compounds that can improve postharvest life. For this, two independent assays were performed, where the antioxidant activity, total phenols and grown-quality parameters were measured. A randomized design was performed, where the main factor corresponded to NaCl doses (0, 25, 50, 100 mM) and UV-B radiation dose (0, 34.5, 61.2, 70.8 kJ m-2). In salt and UV-B treatments a decrease in the leaf size was observed, although in both cases the dry matter increased directly proportional to the salinity content and accumulated radiation. In 100 mM NaCl, lettuces showed total phenols and antioxidant capacity two-folds higher than control. In UV-B treatment, a significant increase of antioxidant activity and total phenols were observed in 34.5 kJ m-2 compared to the control. However, it was observed than 61.2 and 70.8 kJ m-2 decreased antioxidant capacity compared to control and low UV-B.