Preparation and characterisation of fish skin collagen–chitosan–cinnamon essential oil composite film

The composite film with collagen as the main component has been widely used due to its characteristics of non-toxicity, environmental protection and health. Fish skin, a by-product of fish, is an excellent source of collagen. Thus, collagen was extracted from an under-utilised species, Atlantic cod (Gadus morhua) skin, and the composite film of fish skin collagen–chitosan–cinnamon essential oil was prepared by casting. The effects of the ratio of collagen to chitosan (2:8, 4:6, 5:5, 6:4, 8:2) and the concentration of essential oil (0%, 0.1%, 0.2%, 0.3%, and 0.4% (v/v)) on the composite film were studied. The structures of the composite films were analysed using scanning electron microscopy (SEM), Fourier transforms infrared spectroscopy (FTIR), and X-ray diffractometry (XRD). The collagen content of Atlantic cod skin is approximately 50.12%, which is significantly higher than that found in basa fish and Nile tilapia (P < 0.05). The content of hydroxyproline was 4.51%. Analyses of tensile strength, elongation at break, water vapor permeability, and water solubility showed Co4Ch6 (Co:Ch = 4:6) had the optimal comprehensive performance, and Co4Ch6–0.2 (Co4Ch6 with 0.2% CEO) had high water resistance in the high-humidity environment. As the CEO concentration rose, the composite films' infrared absorption bands were enhanced in amplitude, and the XRD peaks were gradually intensified, indicating the internal crystallinity and, thereby, the opacity of the composite films were improved. The bacteriostasis zones Co4Ch6–0.4 against Escherichia coli and Staphylococcus aureus were 2.02 cm and 1.73 cm, respectively. The DPPH radical scavenging rate of Co4Ch6 rose with the increase in CEO concentration, and the DPPH radical scavenging rate of C04Ch6–0.4 was up to 48.56%. Thus, the composite films prepared from fish skin collagen, chitosan, and cinnamon essential oils have outstanding mechanical properties, barrier ability, and antimicrobial activity and are promising for application in food packaging and storage. In addition, the composite films showed a potential antioxidation ability, which might be used as green bioactive films to preserve nutraceutical products.