3.3.7. Antioxidant Activity

Figure 5 shows the antioxidant activity of the PCL-based films during 24 h of contact with DPPH*·* free radicals solution. According to the results, the unloaded PCL film presented a certain level of antioxidant activity (6.12%) after 24 h. However, the antioxidant activity of the plain PCL film was very weak and might be attributed to a DPPH*·* absorption by the film during the contact [51]. The antioxidant activity of the films was achieved when SE was incorporated into the PCL matrix, as expected according to the free radical neutralizing effect of the unloaded SE. Namely, the increase in the loaded SE content led to a significantly stronger (*p* < 0.05) free radical scavenging activity of the films (Figure 5). Also, it may be noted that the DPPH*·* free radicals scavenging ability of the studied systems was more pronounced with an increase in the contact time. This behavior can be explained by release of active compounds from the films into the free radicals solution which allows rapid inhibition or quenching of DPPH*·* radicals [57]. In particular, the antioxidant activity after 0.5 h of the contact between the free radicals solution and the films loaded with 5%, 10%, and 20% SE was increased from 13.32%, 22.64%, and 53.88%, respectively to 28.89%, 47.17%, and 85.27%, respectively after 24 h. This is in the agreemen<sup>t</sup> with a study on chitosan films containing caraway essential oil and beeswax [58] which also reported an increase in antioxidant activity of the films during incubation time. The obtained results point out the efficiency of the PCL-based films containing SE in free radicals neutralization, suggesting their potential role in prevention of oxidation processes in food products.

**Figure 5.** Antioxidant activity, expressed as DPPH*·* free radicals scavenging ability of the PCL-based films. Different letters indicate significant difference among different films at certain incubation time (*p* < 0.05). Different numbers indicate significant difference of the same sample at different incubation time (*p* < 0.05).
