pH-responsive antibacterial emulsion gel based on cinnamaldehyde and carboxymethyl chitosan for fruits preservation...

Although the natural antibacterial agent, cinnamaldehyde, has been extensively studied in the field of food packaging, its water solubility and instability limit its further applications. The controllable responsive release can be achieved through encapsulation in responsive emulsion systems based on carboxymethyl chitosan. Herein, a pH-responsive antibacterial emulsion gel was constructed from cinnamaldehyde-loaded oil-in-water emulsion templates. The interfacial imidization between carboxymethyl chitosan and cinnamaldehyde forms a pH-responsive Schiff base and further stabilizes the emulsion. To immobilize the droplets, acrylamide was subsequently added and polymerized. Such a double network design gives materials adjustable mechanical strength in addition to sealing off the cinnamaldehyde droplets in the network to postpone their release. According to the results of the tensile and compressive cycle, this material has good fatigue resistance. Furthermore, the antibacterial results showed that this material has a 15-day antibacterial cycle and long-lasting antibacterial qualities. In practical applications, acidic moisture from the fruits' respiration decomposes Schiff base bonds and accelerates the release of cinnamaldehyde. The results of cinnamaldehyde release proved that the emulsion gel was pH-responsive, and the dynamic covalent network and emulsion encapsulation technology prolonged the release period of cinnamaldehyde. The mechanical test results proved that the acrylamide network structure gave the material good mechanical properties. Using longan and citrus fruits as examples, we found emulsion gel can significantly prolong the life of fruits by two to three times.