Preparation of Slow-Release Polylactic Acid Antibacterial Active Packaging Films and Its Application in Spinach Preservation

Using nanoparticles or adsorption carriers to load actives substance instead of direct adding into the packaging films can slow down its release. In this study, halloysite nanotubes (HNTs) with acid etching treatment were used as an adsorption carrier to load oregano essential oil (OEO). The polylactic acid (PLA) film containing acid-etched HNTs loaded with OEO (consisting 2.5% acid-etched HNTs and 5% OEO) was prepared through melt extrusion casting method. The loading capacity of OEO in HNTs increased from 6.8 to 23.2% after acid etching treatment. The addition of acid-etched HNTs promoted the dispersion of OEO in the PLA matrix. The Fourier transform infrared spectroscopy showed the interactions among OEO, acid-etched HNTs, and PLA via hydrogen bonds. The PLA films added with OEO or acid-etched HNTs loaded with OEO both exhibited excellent anti-ultraviolet property. Compared with the PLA film containing OEO only, the film containing OEO and acid-etched HNTs exhibited lower tensile strength and elongation at break, achieved slower release of OEO in food simulant (10% ethanol), and showed lower antibacterial activity, which was closely related to their release behavior. However, there were no significant differences in oxygen and water vapor permeability between these two films. In addition, the application of these films on spinach packaging stored at 4 °C for 15 days were studied. The results showed that the film containing OEO and acid-etched HNTs exhibited the best maintenance for spinach quality by inhibiting its respiration rate, weight loss, browning, and microbial growth. It might be related to the gas permeability of the film and the release behavior of OEO from film. This study offered a great potential to develop controlled release PLA active films for vegetable packaging through melt extrusion method.