## 1 Introduction
Meanwhile, copper nanoparticles have been some of the most evaluated nanoparticles: it has been shown that when applied at low concentrations in seeds or soil, it improves plant growth and increases the content of chlorophyll, phenolic compounds, and some enzymes such as CAT, SOD, and PAL [2; 11; 12; 13]. Cu NPs are considered to have stimulatory effects to induce antioxidant compounds [9]. The nanoparticles can cross cell walls [10] by several ways: endocytosis, pore formation, carrier proteins, or through plasmodesmata [14]. These nanoparticles can interact with the intracellular structures [10], stimulating the formation of ROS, which in turn activates the plant defense system generates enzymatic and non-enzymatic antioxidant compounds [9]. It has been reported in maize that CuO NPs are translocated from roots to shoots in hydroponic culture and cause root and shoot biomass decreases [15]. However, few long-term studies have shown the potential toxicity of NPs over the complete life cycle of the plants [16]. Moreover, the Cu NPs have a direct effect on fruit quality during storage. It has been demonstrated that application of these NPs increase pH and lycopene in tomato fruits [2] and diminish weight loss in jalapeno pepper [11]. This positive effect can be observed under light stress conditions by NPs, but can change under conditions of high stress where the activity of the antioxidant enzymes decreases due to the oxidative explosion [9]. Thus, it is possible to find different effects on antioxidant capacity depending on the dose of NPs used. There are very few studies on the effect of NPs on plants subjected to saline stress. Some studies report that ZnO NPs in concentrations of 15 to 30 mg L\({}^{-1}\) have positive effects on the metabolism of tomato plants under saline stress [17]. Likewise, it has been shown that concentrations of 0.05 to 2.5 mg L\({}^{-1}\) of Ag NPs could improve the tolerance of tomato plants to salinity [18]. In canola crop, application of 200 and 1000 mg kg\({}^{-1}\) of CeO\({}_{2}\) NPs improved the growth and physiology of plants under saline stress but did not completely alleviate it [19]. Although the use of NPs in conjunction with salinity stress has been studied, few investigations consider the effect on the behavior of the bioactive compounds in the post-harvest life of the fruits. Recently, the effect of the application of Cu NPs on PVA chitosan hydrogels in certain post-harvest characteristics of the jalapeno pepper was studied [11]. However, the analysis of the bioactive compounds was not considered when the fruits were stored. Although the effect of Cu NPs on several crops has been studied, it is of utmost importance to study the postharvest life of products that serve as food for humans, since they directly influence human health. In addition, the effect of saline stress on the quality of food produced should also be considered. Therefore, the objective of this work was to evaluate the effects on bioactive compounds of tomato fruits stored during different times and conditions, obtained from tomato plants developed under conditions of saline stress and with the application of copper nanoparticles.