## 3 Results and Discussion
Finally, at 23 days of storage, the fruits of the plants with NaCl again showed the highest \(\beta\)-carotene content. This suggests that salinity stress induces the formation of this compound in fruits stored in refrigeration for more than 15 days. The carotenoids are the most representative group of tetraterpenes [37]. \(\beta\)-carotene is the most important carotenoid for human diet and along with lycopene is the most important carotenoid in tomato fruits [1; 3]. These compounds are biosynthesized from just two C\({}_{5}\) precursors: isopentenyl diphosphate (IPP) and dimethylallyl diphosphate (DMAPP). The biosynthesis of these universal terpene precursors via mevalonate [37]. Therefore, the production of these carotenoids is probably more related to oxidative stress responses caused by Cu NPs [10]. As with the previous compounds, there were also statistical differences between treatments at all evaluation times of vitamin C content (Table 5). At the time of harvest, the fruits of the plants with NaCl application only had the lowest content of vitamin C. The rest of the treatments were statistically equal. After eight days of storage at room temperature, the fruits of the plants with NaCl application had the lowest vitamin C content. Under this condition, the fruits of the plants with application of Cu NPs were significantly higher than those of the rest of the treatments. However, under refrigeration, the T0 showed the highest content of vitamin C, while the fruits with application of Cu NPs and NaCl had the lowest content. \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 & 1.17 \(\pm\) 0.02 a & 0.98 \(\pm\) 0.01 a & 1.74 \(\pm\) 0.01 a & not done \\  & NaCl & 0.99 \(\pm\) 0.07 c & 0.80 \(\pm\) 0.01 c & 1.56 \(\pm\) 0.10 b & not done \\  & NPs Cu + NaCl & 1.08 \(\pm\) 0.02 b & 0.95 \(\pm\) 0.01 a & 1.60 \(\pm\) 0.04 b & not done \\  & T0 & 1.13 \(\pm\) 0.02 ab & 0.89 \(\pm\) 0.01 b & 1.33 \(\pm\) 0.01 d & not done \\ \hline \multirow{4}{*}{Refrigeration} & NPs Cu & not done & 0.80 \(\pm\) 0.01 c & 1.17 \(\pm\) 0.01 e & 1.31 \(\pm\) 0.01 c \\  & NaCl & not done & 0.60 \(\pm\) 0.01 d & 1.32 \(\pm\) 0.01 d & 1.36 \(\pm\) 0.01 a \\  & NPs Cu + NaCl & not done & 0.59 \(\pm\) 0.02 d & 1.32 \(\pm\) 0.04 d & 1.28 \(\pm\) 0.02 d \\  & T0 & not done & 0.83 \(\pm\) 0.06 c & 1.47 \(\pm\) 0.02 c & 1.34 \(\pm\) 0.01 b \\ \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 4: \(\beta\)-carotene content (milligrams 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%).