A double cross-linked film based on carboxymethyl chitosan binding with L-cysteine/ oxidized konjac glucomannan with slow-release of nisin for food preservation

In order to address the issue of food contamination by microorganisms and effectively harness the antibacterial properties of nisin, we attempted to incorporate nisin into natural polymer films while addressing its inherent instability. An antibacterial food packaging film based on carboxymethyl chitosan (CCS) binding with L-cysteine (CYS) and oxidized konjac glucomannan (OKG) was developed through both Schiff base reaction and addition reaction of thiol aldehyde. To analyze the effect of addition reaction of thiol aldehyde on the CCS-CYS/OKG films' physicochemical properties, the CCS-CYS was prepared with different CYS combination rates, which were further used to fabricate composite films. It is found that the incorporation of CYS improved the mechanical properties of CCS-CYS/OKG films and facilitated the formation of a denser network structure. The incorporation of CYS also enhanced the film's ultraviolet barrier property, swelling behaviors, as well as loading and release capacity of nisin. As the CYS binding rate of 22.76 %, the CCS-CYS(2)/OKG film exhibited an efficient loading capacity for nisin at 91.53 % with a sustained release over 240 min. Kinetic model analysis revealed that nisin was released through non-Fickian diffusion, mainly driven by gradient concentration and osmotic pressure. Furthermore, the CCS-CYS(2)/OKG-nisin film also displayed significant antibacterial activity against Staphylococcus aureus with an inhibition zone diameter of 22.63 mm at 10 h, thereby, that was also successfully employed for salmon preservation.