## 3 Results and Discussion
Again, since the active packaging always had a higher ratio area between 1655 and 1439 cm\({}^{-1}\) bands compared to LDPE-packaged samples, it can be confirmed that the active packaging provided an effective reduction in unsaturation of fats as a consequence of their oxidation. Figure 5: Superimposed Raman spectra on different days of meat samples stored in conventional LDPE (**left**) and active packaging (**right**) showing the decrease in the 1655 cm\({}^{-1}\) band (C=C stretching) compared to the normalized 1439 cm\({}^{-1}\) band (CH\({}_{2}\) scissoring) chosen as reference. The quantitative analysis of unsaturation was performed as follows: first, the protective effect of the active packaging was evaluated by dividing the area ratio of bands at 1655/1439 cm\({}^{-1}\) of conventional LDPE vs. active packaging samples. The lower the value, the better the performance of the active packaging in preventing lipid oxidation. In addition, the relative change of unsaturation (RCU%) over time was calculated for each series of samples according to the equation: RCU% = ((AR\({}_{0}-\mathrm{AR}_{n}\))/AR\({}_{0}\)) \(\times\) 100, where AR\({}_{0}\) and AR\({}_{n}\) are the area ratios between the 1655 and 1439 cm\({}^{-1}\) shifts corresponding to day 0 and after \"\(n\)\" days of storage, respectively. In this case, the higher the value, the more pronounced the oxidative degradation of the fat. All the results, expressed in percentages, are shown in Table 2. The results over time showed a significant efficacy of the active packaging. In addition, the RCU% values indicated an increase in saturation between samples of the same type with increasing storage time. The results always showed lower RCU% values for active packaging samples compared to LDPE-packaged meat. The quantification of MDA was performed by external calibration based on the measurement of absorbance. The linearity of the calibration curve was obtained in the range of 0.09-0.81 ug\(\cdot\)g\({}^{-1}\) nominal concentrations with regression coefficient (r) 0.9990. Figure 7 shows the obtained values of TBARS for the meat samples stored in different packages during the 16 days of storage. \begin{table}
\begin{tabular}{c c c} \hline
**Day** & **RCU\% (LDPE)** & **RCU\% (Active Packaging)** \\ \hline
0 & \(0\pm 0\) & \(0\pm 0\) \\
7 & \(19\pm 3\) & \(1\pm 0\) \\
9 & \(51\pm 9\) & \(30\pm 3\) \\
11 & \(66\pm 9\) & \(44\pm 5\) \\
14 & \(71\pm 12\) & \(51\pm 10\) \\
16 & \(74\pm 14\) & \(49\pm 10\) \\ \hline \end{tabular}
\end{table} 
Table 2: Results of unsaturation analysis of meat samples based on the SERS measurement of area ratio between 1655 and 1439 cm\({}^{-1}\) bands. All results are expressed as mean \(\pm\) standard deviation (in percentage). Figure 6: Results of SERS analysis of meat samples from LDPE and active packaging expressed as average area ratio (1655/1439 cm\({}^{-1}\) shifts) \(\pm\) standard deviation, \(n=3\). An increasing trend was observed compared to the day 0 samples. As expected, lipids underwent oxidation with the subsequent production of TBARS during the storage time, although the rate of TBARS formation varied among samples. The RSD% ranged from 11% (conventional LDPE) to 17% (active packaging samples). The \(t\)-test was used to compare the average values of the LDPE stored samples and those with active packaging. It was clear that the TBARS results were inconclusive and the inherent limitations of the method (some fats do not produce MDA, some food additives may react with MDA leading to an underestimation of results, and thiobarbituric acid may react with other food components) were noted.