## 3 Results and Discussion
### Oxidative Stability Study of Packaged Fried Almonds  
#### 3.2.1 PV, AV and Hexanal Content  
Hydroperoxides are the primary products of lipid oxidation and PV can be used as an oxidative index for the early stages of lipid oxidation. Autoxidation reaction leads to the formation of a broad range of carbonyl compounds, hydrocarbons, furans and other products that contributes to the rancid taste of nuts [62; 63]. AV indicates the degree of unsaturation in fat food, being usually used to measure secondary oxidation products formation such as aldehydes. Finally, hexanal content was used as a rancidity indicator since it is a secondary metabolite of lipid oxidation which is formed from the breakdown of linoleic acid peroxides [64].  
Figure 4 shows the evolution of fried almonds packaged with neat PCL and the active PCL/ASE films over the storage time, in terms of PV, AV and hexanal content. The initial PV (day 0) of fried almonds was relatively high (\(9.4\pm 0.4\) meq O\({}_{2}\) kg\({}^{-1}\) almond oil) which is indicative of an advanced degree of lipid oxidation as a consequence of almonds processing at high temperatures during frying. [PERSON] et al. reported initial PVs lower than 0.5 meq O\({}_{2}\) kg\({}^{-1}\) almond oil for different raw almonds [65]. The peroxide concentration for all samples reached a maximum after 17 days and then it started to decrease up to 56 days. In this case, hydroperoxides may appear only transitorily and they may rapidly decompose into volatile and non-volatile products after 17 days of oxidative treatment. Throughout the experiment, fried almonds packaged in neat PCL showed significant higher PVs compared to the samples stored in active packaging systems. The behaviour shown between 17 and 56 days, with a decrease between 17 and 33 days followed by an increase up to 56 days, may be explained by the fact that peroxides are instable and they can be further degraded to other compounds such as aldehydes and ketones; even while new peroxides are produced [64].  
Figure 4: PV, AV and hexanal content for fried almonds packaged with neat PCL (), PCL3 () and PCL6 () at 0, 7, 17, 33 and 56 days of oxidative treatment at 40 \({}^{\circ}\)C. Mean \(\pm\) SD; n = 3.  
On the other hand, the concentration of aldehydes formed from the peroxides decomposition, measured by AV and hexanal content (Figure 4), significantly increased from day 17 reaching a maximum value at the end of the shelf-life study (56 days). Similar results were obtained by [PERSON] et al. (2016) when studying the oxidation of Brazil nuts during 21 days of storage at 80 \({}^{\circ}\)C, obtaining a maximum PV after 16 days of oxidative treatment and a noticeable increase in AV and hexanal markers from the 12 th day. In general, a similar oxidation tendency was observed for neat PCL and PCL/ASE films. Nevertheless, neat PCL showed higher AV and hexanal content at the end of the study (\(16.5\pm 1.4\) and \(25.7\pm 2.6\) mg hexanal kg\({}^{-1}\) fried almond, respectively), which can be related to a higher rancidity of fried packaged almonds. Regarding active films, no significant differences (\(p>0.05\)) were observed between films containing 3 and 6 wt.% ASE showed AV values of \(8.1\pm 1.3\) and \(7.3\pm 0.2\), respectively; and hexanal contents of \(19.8\pm 2.4\) and \(20.4\pm 1.2\) mg hexanal kg\({}^{-1}\) fried almond, respectively. This fact was indicative of a higher extent of oxidation in fried samples packaged into neat PCL compared to samples packaged in active packaging systems which showed some antioxidant effect. These results are in agreement with previous ones obtained for radical-scavenging activity of PCL3 and PCL6 due to the antioxidants present in ASE. Similarly, [PERSON] et al. (2016) reported that films containing antioxidants isolated from barley husts were effective in slowing down lipid hydrolysis and primary and secondary lipid oxidation processes of packaged cod fillets during 12 months of frozen storage at -20 \({}^{\circ}\)C.