Optimization of low-temperature plasma-modified preparation and structural characterization of potato starch films

Potato starch can be widely expected to serve as the new alternative packaging material in food preservation in recent years, due to its excellent properties. The endogenous phosphate groups of potato starch can be ionically bonded to the surrounding polar hydroxyl groups. However, the research on potato starch is limited by the high water absorption and low gas resistance. Fortunately, the low-temperature plasma technology can be used to modify the potato starch for easy oxidation, cross-linking, depolymerization, the increase or decrease of hydrophilicity, and the introduction of functional groups, particularly for the better surface properties of potato starch. Cinnamon Essential Oil (CEO) can be added to the potato starch film as a bacteriostatic agent, in order to inhibit the activity of pathogenic, as well as decaying fungi and bacteria for better food safety. Nano-silica (SBA-15) can be used to wrap the Cinnamon Essential Oil (CEO) for slow and controlled release. The surface of SBA-15 often contains a large number of unsaturated residual bonds and weak acidic free Si-OH in the different bonding states. However, a large specific surface area of the SBA-15 is easy to agglomerate in the aqueous solution. The carboxyl group on the surface of modified potato starch is the hydrogen bond with the polar hydroxyl group on the surface of SBA-15. It is very necessary to improve the dispersion of CEO-SBA-15 in the potato starch film, together with the physical properties of the composite film. In this study, the modified CEO-SBA-15/potato starch film was prepared by low-temperature plasma modification. The investigation factors were taken as the plasma treatment time and the dosage of potato starch, glycerol, and CEO-SBA-15. The performance of the composite film was then optimized and screened by the single factor, orthogonal, and verification experiment. The optimized composite films were characterized by the surface morphology (Scanning Electron Microscope, SEM), phase change (X-Ray Diffraction spectroscopy, XRD), as well as the chemical bond and functional group (Fourier Transform Infrared Spectroscopy, FTIR). A systematic evaluation was performed on the oxygen and water vapor permeability, swelling degree, water solubility, opacity, tensile strength, UV spectrum, and Thermogravimetric analysis (TG). The results showed that the duration was 6 min for the optimum factor ratio in the preparation of modified potato composite film using the low-temperature plasma technology. The dosages of potato starch, glycerol, and CEO-SBA-15 were 5, 1.5, and 0.5 g/100 mL, respectively. The SEM images showed that there were circular depressions on the surface of plasma-treated potato starch. The CEO-SBA-15 was evenly dispersed in the composite film prepared by the plasma-treated potato starch solution. The XRD and FTIR showed that the plasma-modified potato starch formed a strong hydrogen bond with the CEO-SBA-15. The plasma-modified potato starch shared the formation of an oxidized carboxyl group and the reduction of a hydroxyl group. Ultraviolet (UV) spectrum analysis showed that the plasma-treated composite film presented better UV resistance and light transmittance. The TG showed that the plasma-modified potato starch composite film had better thermal stability. In addition, the physical properties were greatly improved in the potato starch composite film prepared by the plasma system. The oxygen permeability, water vapor permeability, and swelling degree of the composite film were reduced by 4.32 g(m2•h), 7.48 g(m2•h), 79.15%, respectively, while the tensile strength of the composite film increased by 2.9 MPa, compared with the unmodified composite film. The finding can provide a strong reference to better protect the food contents from external factors and mechanical damage.