## 3 Results
### Permeability Properties  
In general, if the permeability of the active packaging to oxygen from the external environment increases, perishable foods will be more rapidly subjected to oxidative and degradative phenomena, including microbial proliferation, with a strong reduction of food shelf-life. On the other hand, for those products packaged in a modified atmosphere, the packaging must prevent a fast release of the inert gases from the environment surrounding food (having protecting effects on food) to the external environment.  
The oxygen permeability measurements were initially carried out on pure polymer samples, to conduct a feasibility study of the measurements. The zein films made by  
Figure 7: Results of the release tests on films obtained by electrospinning in ethanol 10% (_v/v_), in terms of: (**a**) caffeine released per kg of film, (**b**) radical ABTS\({}^{\bullet}\): inhibition. Different symbols indicate statistically significant differences among values over time (_p_ < 0.05) of dataset with the same extract loading.  
electrospinning, being porous materials, were found to be completely transparent to the gas flow. The tests carried out on the samples produced by solvent casting, on the other hand, were strongly affected by the inhomogeneity of thickness. Therefore, after having optimized the last aspect by associating the solvent casting technique with that of spin coating, the oxygen permeability measurements were carried out systematically on these latter samples. The OPC and OTR were measured from the pressure rise in a known volume applying 1 atm of differential pressure of O\({}_{2}\) across the zein film at different percentual composition of SCG, from 0 to 45% [30]. In Table 2 the results are reported for films produced by spin coating with zein enriched with different concentration of SCG.  
In Table 2, OPC is reported in m\({}_{\text{STP}}\)\({}^{3}\) m/(m\({}^{2}\) s Pa), OTR in m\({}_{\text{STP}}\)\({}^{3}\)/m\({}^{2}\) s and cc/(m\({}^{2}\) day) as they are units most often used in film packaging technology. However, a unit conversion in SI is reported as the Table note. As for all polymers, zein suffers from physical aging depending on the quantities of the adsorbed gas, especially for condensable gases such as CO\({}_{2}\) or O\({}_{2}\) that can induce plasticization. Plasticization is based upon molecular chain reorganization of a polymer induced by high sorption of a condensable gas [44]. This phenomenon ensues instability of the permeation properties over time. Considering the experimental procedure adopted, the obtained data are free from artefacts with respect to the physical aging of zein [45].  
The value of OPC for pure zein film agrees with literature results [45]. As expected, these values decrease by increasing the percentage of SCG extract, consequently improving the oxygen barrier action. The trend changes increasing quantity of extract over 35%. At values equal or higher than 45% \(w/w\), it is possible that the quantity of SCG extract generates a swelling of the polymer allowing it to increase gas diffusion.  
Comparing our permeability data with those of other materials often used in food packaging, such as low-density polyethylene (LDPE) or Polyethylene terephthalate (PET), the spin coating films can provide an equal, or increased oxygen barrier [46].