## 4 Discussion  
In all presented studies, TBARS analysis was applied to food samples to quantify MDA, which is considered to be the main oxidation product of PUFAs, in different types of matrices (meat [14; 15; 16] and egg yolk [8]). In the case of milk, which is a rich source of MUFAs, lipids oxidation led to different compounds compared to other foodstuffs and the TBARS method was adapted in order to obtain a simple and rapid method to quantify the main milk oxidation products (e.g., saturated aldehydes). Considering this, four parameters (trichloroacetic acid concentration (TCA), antioxidant type, incubation time, and thiobarbituric acid (TBA) concentration) were modified for establishing the optimum analytical conditions for milk TBARS determination. Differently to meat and egg samples, due to milk's specific fatty acid composition (higher proportion of MUFAs, lower proportion of PUFAs), MDA was no longer the major oxidation product. After TBA incubation, the colour of the milk sample solution turned yellow and on absorption spectra two more peaks at approximately 450 and 495 nm, with absorbance values much higher than the absorbance at 532 nm were registered [12; 18]. A possible explanation could be the forming of saturated aldehydes, the major reaction products derived from MUFAs, during milk oxidation. After TBA incubation, a yellow complex (saturated aldehydes-TBA) was obtained, with a maximum absorption peak at approximatively 450 nm. Along with the saturated aldehydes derived from MUFAs peroxidation, studies showed that hexanal, which is the major oxidation product of linoleic \begin{table}
\begin{tabular}{c c c c c c c c c c c} \hline \hline
**Variables** & **SFAs (\%) \({}^{1}\)** & **MUFAs (\%) \({}^{2}\)** & **PUFAs (\%) \({}^{3}\)** & **\(\Omega\)(\%) \({}^{4}\)** & **\(\Omega\) (\%) \({}^{5}\)** & **Def/\(\Omega\) \({}^{3}\)** & **A550 (nm) \({}^{7}\)** & **A4950 (nm) \({}^{8}\)** & **A532 (nm) \({}^{9}\)** & **MDA (Hg/L) \({}^{10}\)** \\ \hline SFAs (\%) & 1 & \(-0.9809\) & \(-0.9891\) & \(-0.9796\) & \(-0.9856\) & \(0.3245\) & \(-0.9841\) & \(-0.9812\) & \(-0.9971\) & \(-0.9910\) \\ MUFAs (\%) & \(-0.9809\) & 1 & \(0.9939\) & \(0.9980\) & \(0.9757\) & \(-0.3776\) & \(0.9946\) & \(0.9933\) & \(0.9763\) & \(0.9845\) \\ PUFAs (\%) & \(-0.9891\) & \(0.9939\) & 1 & \(0.9958\) & \(0.9939\) & \(-0.3111\) & \(0.9992\) & \(0.9985\) & \(0.9913\) & \(0.9975\) \\ T3 (\%) & \(-0.9796\) & \(0.9980\) & \(0.9958\) & 1 & \(0.9811\) & \(-0.3330\) & \(0.9957\) & \(0.9974\) & \(0.9779\) & \(0.9878\) \\ O6 (\%) & \(-0.9859\) & \(0.9757\) & \(0.9939\) & \(0.9811\) & \(-0.2446\) & \(0.9917\) & \(0.9912\) & \(0.9943\) & \(0.9984\) \\ He/(\(\Omega\)) & \(0.3245\) & \(-0.3776\) & \(-0.3111\) & \(-0.3330\) & \(-0.2446\) & \(1\) & \(-0.3310\) & \(-0.2873\) & \(-0.2736\) & \(-0.2919\) \\ A450 (nm) & \(-0.9841\) & \(0.9946\) & \(0.9992\) & \(0.9957\) & \(0.9917\) & \(-0.3310\) & \(1\) & \(0.9981\) & \(0.9865\) & \(0.9957\) \\ A495 (nm) & \(-0.9812\) & \(0.9933\) & \(0.9985\) & \(0.9974\) & \(0.9912\) & \(-0.2873\) & \(0.9981\) & \(1\) & \(0.9846\) & \(0.9941\) \\ A532 (nm) & \(-0.9971\) & \(0.9763\) & \(0.9913\) & \(0.9779\) & \(0.9943\) & \(-0.2736\) & \(0.9865\) & \(0.9846\) & \(1\) & \(0.99957\) \\ MDA & \(-0.9910\) & \(0.9845\) & \(0.9975\) & \(0.9878\) & \(0.9984\) & \(-0.2919\) & \(0.9957\) & \(0.9941\) & \(0.9957\) & \(1\) \\ \hline \hline \end{tabular}  
* \({}^{1}\) Saturated fatty acids, \({}^{2}\) monounsaturated fatty acids, \({}^{3}\) polyunsaturated fatty acids, \({}^{4}\) omega 3 fatty acids, \({}^{5}\) omega 6 fatty acids, \({}^{6}\) ratio between omega 6 and omega 3 fatty acids, \({}^{7}\) absorbance read at 450 nm, \({}^{8}\) absorbance read at 495 nm, \({}^{9}\) absorbance read at 532 nm, \({}^{10}\) malondialdehydedehyde concentration expressed as \(\mu\)g/L.  
\end{table} 
Table 6: Correlation matrix describing the interrelation between quality of lipids and oxidation parameters.