## 3 Results and Discussion
\begin{table}
\begin{tabular}{c c c c c c} \hline
**Storage** & **Treatment** & **0 ds** & **8 ds** & **15 ds** & **23 ds** \\ \hline \multirow{4}{*}{Room temperature} & NPs Cu & 33.25 \(\pm\) 0.27 ab & 20.75 \(\pm\) 0.40 b & 26.12 \(\pm\) 0.40 b & not done \\  & NaCl & 32.89 \(\pm\) 0.32 b & 13.75 \(\pm\) 0.41 f & 19.11 \(\pm\) 0.41 f & not done \\  & NPs Cu + NaCl & 33.84 \(\pm\) 0.31 a & 14.28 \(\pm\) 0.50 ef & 19.65 \(\pm\) 0.50 ef & not done \\  & T0 & 33.49 \(\pm\) 0.52 ab & 15.72 \(\pm\) 0.31 d & 21.08 \(\pm\) 0.31 d & not done \\ \hline \multirow{4}{*}{Refrigeration} & NPs Cu & not done & 17.09 \(\pm\) 0.36 c & 22.45 \(\pm\) 0.36 c & 38.37 \(\pm\) 0.23 a \\  & NaCl & not done & 17.24 \(\pm\) 0.47 c & 22.60 \(\pm\) 0.47 c & 36.82 \(\pm\) 0.32 ab \\ \cline{1-1}  & NPs Cu + NaCl & not done & 14.61 \(\pm\) 0.34 e & 19.98 \(\pm\) 0.34 e & 32.77 \(\pm\) 0.37 b \\ \cline{1-1}  & T0 & not done & 27.73 \(\pm\) 0.44 a & 33.10 \(\pm\) 0.44 a & 34.38 \(\pm\) 4.93 ab \\ \hline \end{tabular}  
* ds: days of storage. NPs Cu: plants without stress and with application Cu nanoparticles to 250 mg L\({}^{-1}\). NaCl: plants with stress by NaCl. NPs Cu + NaCl: plants with stress by NaCl and with application Cu nanoparticles at 250 mg L\({}^{-1}\). T0: absolute control without application of Cu nanoparticles and without stress by NaCl. Each value is expressed as mean \(\pm\) standard deviation (\(n\) = 3). Different letters by column indicate statistical differences between treatments according to [PERSON]’s least significant difference test (\(p\)\(\leq\) 0.05).  
\end{table} 
Table 5: Vitamin C content (milligrams of ascorbic acid per 100 g fresh weight) in tomato fruits at different storage times at room temperature (24 \(\pm\) 1 \({}^{\circ}\)C) and refrigeration (4 \(\pm\) 1 \({}^{\circ}\)C and relative humidity at 80%). At 15 days of storage, the same treatment behavior was observed as in the previous evaluation. At room temperature, the fruits of the plants with NaCl application had the lowest vitamin C content, while the fruits of the plants with application of Cu NPs were significantly superior to the rest of the treatments. Under refrigeration, the T0 presented the highest content of vitamin C, and the fruits of the plants with application of Cu NPs and NaCl had the lowest content. At 23 days after storage in refrigeration, the fruits of plants with application of Cu NPs and NaCl had the lowest content of vitamin C, as it was in previous evaluations under these conditions. However, the fruits of the plants with application of Cu NPs had the highest vitamin C content. These results indicate that the application of Cu NPs increases the vitamin C content when the fruits are stored at room temperature. This may be derived from the induction of antioxidant compounds as mentioned above [11]. This is of great importance since humans must ingest vitamin C through rich sources such as fruits because the human body does not have the capacity to produce it [38]. Specifically in tomato fruits, vitamin C is one of the most important [1]. In the plants, vitamin C is converted from glucose following the pathway that involves the conversion of GDP-D-mannose to GDP-L-galactose catalyzed by a GDP-mannose-30,50-epimerase. L-galactose released from the nucleotide is the immediate precursor of L-galactono-1,4-lactone, which by action of a dehydrogenase is converted to L-ascorbic acid [39]. Thus the induction of this compound is more related to the antioxidant responses of plants [11]. In addition, it was also evident that salinity stress induces a significant decrease of vitamin C in tomato fruits stored at room temperature. This fact is probably due to the high stress generated by an oxidative burst leading to the reduction of antioxidants [9]. In this case, the vitamin C content was affected. Regarding the antioxidant capacity by DPPH, only at 23 days of storage were there no differences between treatments (Table 6).