The effects of carboxymethyl cellulose (CMC: 4–16 wt%), chitin nanofiber concentrations (CHNF: 2–5 wt%) and Trachyspermum ammi (Ajowan) essential oil (AJEO: 0.26–1 v/v%) on the physical and antimicrobial characteristics of the gelatin-based nanocomposite films were studied by response surface methodology (RSM). The optimization was based on maximizing contact angle, ultimate tensile strength (UTS), strain at break (SAB), lightness (L), antibacterial activity, while minimizing water vapour permeability)WVP(, solubility, swelling, yellowness index (YI), and total color difference (ΔE) values. An increase in the CMC/gelatin ratio in the film formulations caused a decrease in WVP, SAB, ΔE, and YI. In addition, the incorporation of CHNF improved their mechanical strength and barrier properties. Furthermore, the addition of AJEO clearly improved the antimicrobial activity against Staphylococcus aureus and Escherichia coli, while reducing the mechanical and light barrier properties. The optimal values of CMC, CHNF and AJEO for composition of the gelatin film were 15.83 (wt%), 3 (wt%) and 0.74 (v/v%), respectively.
