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Highlights Control lettuce showed higher levels of proline than lettuce from other treatments. Well water lettuce exhibited higher levels of phenols than that from other treatments. Lettuce with low-salinity shrimp effluent exhibit a quality comparable to the control.

Chemical elicitors in plants during cultivation have been applied in soil, hydroponic solutions, or sprayed on the leaves to induce physiological changes and stimulate the production of bioactive compounds. Salicylic acid (SA) is a phenolic compound present in plants with multiple functions, including stimulus of plant growth and induction of plant defense responses under conditions of stress. Recently, the use of SA as elicitor has generated much interest, due to the growing number of studies demonstrating its positive effects in fruits, vegetables, and herbs on the induction of phytochemicals, mainly phenolic compounds, alkaloids, saponins, carotenoids, among others. The health benefits of plant materials treated with SA are mainly their antioxidant capacities determined by the 2,2'-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) and 2,2-diphenyl-1-picrilhidrazil (DPPH) assays and anti-inflammatory properties determined in vitro, as well as hypoglycemic and hypolipidemic properties and renal protection evaluated by in vivo studies. Therefore, the exogenous application of SA during cultivation of different plants could be an alternative to increase their economic value and could be the basis for designing standardized procedures in the production of bioactive compounds.

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This paper focuses on the quality of lettuce var. longifolia grown with shrimp effluents from well water (WW), diluted seawater (DSW) and a hydroponic solution (HS). Results evidenced that WW and DSW effluents slightly decreased weight, foliage, and yield (5-9%) in plants compared to HS control. Furthermore, WW-lettuce showed a higher level of total phenolic compounds (~71%), flavonoids (~90%), and antioxidant capacity (0.7-3-folds) than HS-plants, mainly in the soluble fraction. WW-lettuce also showed a higher content of total soluble solids (~16%) and, a lower saturation of color, which correlated significantly (p <0.05) with chlorophyll a. WW-lettuce exhibited the highest concentrations of p-hydroxybenzoic, p-coumaric and ferulic acids, as well as quercetin 3-O-glucoside and quercetin 3-O-ramnoside. Whereas DSW-lettuce showed the highest levels of caffeic acid, isorhamnetin 3-O-glucoside, kaempferol 3-O-glucoside, kaempferol and quercetin. HS-lettuce showed a higher proline content than the lettuces from the other treatments. These results indicate that aquaponic lettuce culture with shrimp effluent from WW could be used as an alternative culture system to reduce land area requirements, decrease or eliminate the discharge and impact of shrimp effluents, and simultaneously improve the functional properties of lettuce.