## 3 Impact of Cold Plasma on Packaging Properties
### Molecular Properties of the Film
Several studies have also reported the modification of protein structure plasma treatment. Similar to starch, the application of cold plasma increased oxygenated groups (C-O and C-O-C) in gluten and whey protein and this was evidenced from the increase in peaks at 1105 cm\({}^{-1}\) and 1048, & 1258 cm\({}^{-1}\), respectively [100]. The characteristic peak in the range of 3700-3000 cm\({}^{-1}\) can be attributed to the N-H and O-H stretching of proteins. Atmospheric cold plasma treatment of zein film showed a shift and slight increase in peak intensity 3300 cm\({}^{-1}\) attributable to increased polar groups on the film surface [80]. Such modifications were also observed from cold plasma treatments of 60 s in composite films like zein/chitosan [94], and zein/PLA [46] where the shift and increase in peak intensity in the region from 3700-3000 cm\({}^{-1}\) indicates the formation of a hydrogen bond between the zein-PLA and zein-chitosan interface. In these studies, it was further reported that the plasma treatment for the 60 s in zein/PLA composite film and 120 s in zein/chitosan treatment showed an extra peak in the carbonyl region 1800-1650 (at 1754 cm\({}^{-1}\)) which could be ascribed to the protein oxidation or peptide bond breakage [46; 94]. [PERSON], [PERSON] [94] also reported that the variation of the peak intensity in the region of 1300-750 cm\({}^{-1}\) (at 1097 cm\({}^{-1}\)) could also be attributed to the interaction between C-O (chitosan) and amide (zein) groups. In the protein structure the FTIR spectrum in the range of 1700-1600 cm\({}^{-1}\) (amide I) corresponds to the secondary structure components (1659-1660 cm\({}^{-1}\): \(\alpha\)-helix; 1660-1670 cm\({}^{-1}\): \(\beta\)-turn; 1610-1640 cm\({}^{-1}\): \(\beta\)-sheet; and 1640-1650 cm\({}^{-1}\): random coil) and 1600-1500 cm\({}^{-1}\) (amide II) refers to N-H bending and C-N stretching modes indicates the environment for hydrogen bonding [80; 94; 104]. It has been reported that the application of cold plasma transformed or rearranged the secondary structure components into a \(\beta\)-sheet structure. [PERSON], [PERSON] [104] investigated the impact of DBD atmospheric cold plasma on sodium caseinate film and reported that the peak intensity in the region of 1637-1645 cm\({}^{-1}\) decreased with the increase in plasma treatment and the peak disappeared in the film treated for 10 min, indicating the decrease in random coil content. However the peak intensity at 1623 cm\({}^{-1}\) and 1689 cm\({}^{-1}\) increased for the treatment time of 2.5 to 5 min signifying the increase in \(\beta\)-sheet structure [104]. [PERSON], [PERSON] [80] investigated the impact of atmospheric cold plasma on zein film and reported that with an increase in treatment time (0 to 60 s) \(\beta\)-sheet and random coil content increased by 25.75% and 16.37%, respectively. On the contrary, there was a decline in the \(\beta\)-turn and \(\alpha\)-helix by 13.45% and 20.63%, respectively, indicating the transformation of \(\alpha\)-helix and \(\beta\)-turn into \(\beta\)-sheet and random coil. Similarly, [PERSON], [PERSON] [94] reported the transformation of \(\beta\)-turn and random coil into \(\beta\)-sheet and \(\alpha\)-helix in zein/chitosan film after the application of atmospheric cold plasma for 0-120 s. [PERSON], [PERSON] [105] studied the impact of voltage and treatment time of DBD plasma on casein edible films. It was reported that at a constant treatment time of 60 s with the increase in the voltage from 0 to 70 V, \(\alpha\)-helix and random coil content decreased by 53.78% and 46.83%, respectively, in comparison to control film. Whereas the \(\beta\)-sheet content increased by 67.51%. Similarly, \(\beta\)-turn content increased by 20.95% up to a voltage of 60 V and then decreased by 20.95% when the voltage was increased to 70 V. Such a result indicates the transformation of \(\alpha\)-helix into \(\beta\)-sheet.