## 3 Results
### Nanemulsion Stability During Storage
#### 3.2.2 Chemical Stability  
Deterioration of Lycopene Concentration and Nanoemulsion's Color During Storage  
The change in lycopene concentration as a function of time in the nanoemulsions followed first-order kinetics (linear change of \(\ln\)C\({}_{\text{lycopene}}\) as a function of time) at all experimental conditions investigated (Figure 3), in agreement with similar studies [49; 50]. The type of oil, the incorporation of AA, and the temperature significantly affected the deterioration rate of lycopene (\(p<0.05\)), while the pH values did not show a significant effect (Table 3). Fish oil and corn oil nanoemulsions exhibited the highest average deterioration rate, namely FO \(-0.0249\) d\({}^{-1}\) and CO \(-0.0352\) d\({}^{-1}\), while olive pomace, \begin{table}
\begin{tabular}{c c c} \hline \hline
**Samples** & **MDD** & **PDI** \\  & **(nm)** & **PDI** \\ \hline OPO-AA nanoemulsion & \(307.5\pm 10.5\) x & \(0.268\pm 0.006\) y \\ CLA-AA nanoemulsion & \(282.2\pm 4.8\) & \(0.254\pm 0.002\) y \\ SO-AA nanoemulsion & \(287.9\pm 6.3\) x & \(0.254\pm 0.04\) y \\ CO-AA nanoemulsion & \(280.4\pm 5.8\) x & \(0.262\pm 0.08\) y \\ FO-AA nanoemulsion & \(270.4\pm 10.2\) x & \(0.200\pm 0.05\) y \\ \hline \hline \end{tabular}  
* Superscript letters x for MDD and y for PDI represent no significant differences (\(p>0.05\)) between the lipid phases. Data are described as mean value \(\pm\) standard deviation (n = 3).  
\end{table} 
Table 2: Mean droplet diameter (MDD) and polydispersity index (PDI) of olive pomace oil (OPO), canola oil (CLA), corn oil (CO), fish oil (FO), and sunflower oil (SO) nanoemulsions enriched with lycopene and ascorbic acid (AA) after 2 months of storage at 4 \({}^{\circ}\)C.  
Figure 3: Deterioration of lycopene concentrations in (**a**) olive pomace oil (OPO) and (**b**) fish oil (FO) of /w nanoemulsions with or without the addition of ascorbic acid (AA) during storage at 25 \({}^{\circ}\)C and 4 \({}^{\circ}\)C and pH = 2.  
canola oil, and sunflower oil led to the lowest average rates, without significant difference among them, namely OPO \(-0.0221\) d\({}^{-1}\), CLA \(0.0225\) d\({}^{-1}\) (Figure 3), and SO \(-0.0189\) d\({}^{-1}\). As expected, the presence of AA reduced the deterioration rate of lycopene by 57% due to its strong antioxidant activity. Moreover, nanoemulsions exhibited higher chemical stability at refrigerated storage, with an average deterioration rate of \(-0.0185\) d\({}^{-1}\) compared to \(-0.0334\) d\({}^{-1}\) at 25 \({}^{\circ}\)C. Although pH did not significantly affect the deterioration rate of lycopene, at pH = 7 slightly lower rates (\(-0.0231\) d\({}^{-1}\)) were found compared to at pH = 2 and pH = 5; \(-0.0298\) d\({}^{-1}\) and \(-0.0247\) d\({}^{-1}\), respectively (Table 2). Others studies also reported an increased stability of encapsulated lycopene in the nanoemulsions at 4 \({}^{\circ}\)C compared to ambient temperature or abusive conditions of accelerated testing [51,52]. Lycopene degradation can also be visually monitored by the change in color of lycopene nanoemulsions. The increase in whiteness can be correlated with the deterioration of lycopene concentrations in nanoemulsions, as samples underwent oxidative degradation, which disrupts the conjugated double bonds of lycopene. This breakdown causes a shift in the absorption maxima, leading to a fading of its characteristic red/orange hue [25,51,52]. The whiteness index was significantly affected by lipid phase, storage parameters (temperature, storage time), and the presence of ascorbic acid in the nanoemulsions (\(p<0.05\)), while pH value did not significantly affect the color of the nanoemulsions. Ascorbic acid protected the color, as a milder increase in the whiteness index was observed during storage, with the greatest protection being observed under refrigerated storage conditions.