Gelatin film cross-linked with laccase-catalyzed purple cauliflower extract and coated with Zn-carbon dots exhibits excellent physicochemical properties and functionality for intelligent and active packaging

Preparation of oxidized purple cauliflower extract (OPE) was conducted by laccase oxidation and served as a reinforcing agent for enhancing physicochemical properties of gelatin (Gel) films. Chitosan (CS) loaded with biowaste-derived Zn-carbon dots (Zn-CD) coating further enhanced the functionality and stability of Gel/OPE film. Structural characterization revealed that OPE and Gel form Schiff base bonds and hydrogen bonds. After the formation of CS/Zn-CD coating, hydrogen bonds formed between CS and Zn-CD, and CS and Gel were closely bonded through electrostatic interactions and hydrogen bonding. OPE crosslinking and CS/Zn-CD coating improve mechanical, barrier properties and water resistance of Gel films. CS/Zn-CD coating improved antibacterial and antioxidant ability and illumination stability of composite film, effectively reflected the freshness of salmon during storage. Hence, the functional Gel films developed in this study is hopeful candidate for intelligent and active food packaging application. • OPE was prepared using laccase oxidation and Zn-CD was synthesized from biowaste. • Intelligent active film of Gel/OPE film coated with CS/Zn-CD was developed. • Composite film increases physical, antibacterial and antioxidant properties. • CS/CD-Gel/OPE 8 has excellent pH color response, biodegradability, and biosafety. • The intelligent/active packaging film could precisely monitor the salmon freshness.