Colorimetric indicator based on purple tomato anthocyanins and chitosan for application in intelligent packaging.

Intelligent colorimetric indicator films were prepared to monitor freshness/spoilage of milk and fish by incorporating purple tomato anthocyanin (PTA) into chitosan (CS) matrix via solution casting method with PTA concentration (w/w, based on CS) of 10%, 30%, and 50%, respectively. The pH-response, UV absorption, Swelling Index, and the mechanical properties of CS/PTA films were determined. It was found that the color of the original CS/PTA films became darker with an improvement of PTA content and expressed well pH-sensitivity. With increasing of pH, the color of the CS/PTA films exposed to pH = 3-11 solutions became darker and the change in color of the CS/10% PTA film was the most discernable. The tensile strength and Young's modulus of the CS/PTA film was much lower than that of CS film, however, the elongation at breaking and Swelling Index were both improved by adding PTA. The intelligent films with 10% PTA changed their color during progressive spoilage of milk or fish, revealing their potential application for monitoring food freshness/spoilage.

Development of biobased multilayer films with improved compatibility between polylactic acid-chitosan as a function of transition coating of SiOx.

A SiOx coating prepared via plasma-enhanced chemical vapor deposition (PECVD) technique was used as a transition layer between polylactic acid (PLA) and chitosan (CS) to form a three-layer composite film of PLA/SiOx/CS. The effect of oxygen plasma irradiation time (0 s, 30s and 60s) on SiOx surface and PLA-CS interface was examined based on the contact angle, pull-off test and scanning electron microscope (SEM). The mechanical, barrier and antibacterial properties of PLA/SiOx/CS films were also investigated. The results showed that oxygen plasma irradiation improved the hydrophilicity of the SiOx surface and the adhesive strength between SiOx-CS of PLA/SiOx/CS films in a time-dependent manner. SEM examination revealed a gap between PLA/CS layers, but the interfacial separation among layers in PLA/SiOx/CS films disappeared as the transition layer of SiOx and oxygen plasma irradiation (60s) intensified. Notably, the oxygen barrier property and antibacterial activity of PLA/SiOx/CS films were dramatically enhanced. Additionally, moisture resistance was slightly decreased following the incorporation of the CS coating compared with the PLA film. The tensile strength of the composite film also increased with the number of layers, while elongation at break decreased. The prepared PLA/SiOx/CS films with multifunction are promising applied in food packaging as biobased materials.