## 3 Results and Discussion
### Effect of CSS on the Shelf Life of Cooked Chicken Burger Samples  
#### 3.2.1 Thiobarbituric Acid Reacting Substances (TBARS) Test  
The TBARS values of cooked samples are presented in Figure 3. Generally, over time TBARS values increase in all the cases, but the CTRL set showed significantly higher values immediately after cooking (_p_ < 0.05), as well as a statistically significant increase during the refrigerated storage (_p_ < 0.05). In all burgers with CSS, TBARS mean values were lower than the acceptance limit of TBARS for rancidity (1.0 mg MDA(Malondialdehydedehyde)/kg) [45] until 72 h; after 120 h CSS3% showed a TBARS mean value near to the critical content, while this limit was exceeded in all samples without CSS.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Uncooked Samples** & **L*** & **a*** & **b*** & **C*** \\ \hline CTRL & 45.91 \(\pm\) 0.18 a & 0.28 \(\pm\) 0.11 b & 10.95 \(\pm\) 0.53 & 10.96 \(\pm\) 0.53 b \\ CSS 1.5\% & 32.83 \(\pm\) 1.33 b & 3.81 \(\pm\) 1.21 a & 13.74 \(\pm\) 1.58 & 15.42 \(\pm\) 1.82 a \\ CSS 3\% & 29.40 \(\pm\) 0.71 c & 4.96 \(\pm\) 0.83 a & 14.60 \(\pm\) 0.31 & 14.28 \(\pm\) 0.52 a \\ sign. & ** & ** & n.s. & * \\ \hline \multicolumn{4}{c}{**Cooked Samples**} \\ \hline CTRL & 56.12 \(\pm\) 0.76 a & 1.18 \(\pm\) 0.77 & 16.75 \(\pm\) 0.49 a & 16.80 \(\pm\) 1.08 a \\ CSS 1.5\% & 47.35 \(\pm\) 0.44 b & 2.25 \(\pm\) 0.60 & 10.94 \(\pm\) 0.36 b & 11.17 \(\pm\) 0.42 b \\ CSS 3\% & 43.54 \(\pm\) 0.27 b & 2.83 \(\pm\) 0.60 & 12.05 \(\pm\) 0.40 b & 12.38 \(\pm\) 1.22 b \\ sign. & * & n.s. & ** & ** \\ \hline \multicolumn{4}{c}{Legend: data followed by different superscript letters, in the same column, are significantly different (LSD test, \(p\) < 0.05); asterisks indicate significance at *_p_ <0.05; **_p_ < 0.01; n.s. not significant.} \\ \hline \end{tabular}
\end{table}
Table 3: Colour values (mean \(\pm\) SD) of L* (lightness), a* (redness), b* (yellowness), and C* (chroma) for uncooked burgers and cooked burgers, in control (CTRL) and in samples with +1.5% (CSS 1.5%) and +3.0% (CSS 3.0%) of coffee silver skin as ingredient.  
The TBARS test is helpful for a first screening of the oxidation rate of a food, but it does not discriminate which kind of oxidation is occurring. We cannot be sure if what is observed with this assay comes from lipid oxidation itself, or if proteins too have taken part in the process and are the principal cause starting the reactions. As is known, chicken meat is poor in lipids that are mainly unsaturated fatty acids which are the elective substrate for the oxidation. Moreover, [46] have searched for the lipidic profile of CSS and their results show a small content of lipids, which are mainly saturated fatty acids (SFAs). So, one could refer all the defective odours and tastes to the lipidic oxidation complex of reactions. Unfortunately, the oxidation process is very unstable and sometimes unpredictable. Besides lipids, proteins and iron ions boost the process within other factors (rise in temperature, oxygen and light exposure, salt addition, etc.) making TBARS not such an affordable method to establish the lipidic oxidative status of a food [47; 48].  
Anyway, from our results we can imagine that the contribution of CSS to the global oxidation burgers and its lipids increment are almost zero, while its protective effect seems to be promising. This may depend on the high content in phenolic and bioactive species.