Sustained-release composite films incorporated with rosemary (Rosmarinus officinalis L.) essential oil: Characterization, release kinetics and application for cheese preservation

• Rosemary essential oil (REO) at 1.5 % improved the stability of the chitosan biofilm, elasticity (12 %), and vapor barrier (75 %). • REO films showed 50 % antioxidant activity and strong antimicrobial effects. • Sustained and controlled REO release via Fickian diffusion (R² = 0.98–0.99). • Chitosan biofilms with REO extended shelf life of high-moisture, high-fat cheese by 12 days. In this study, active sustained-release films based on chitosan/starch were developed, incorporating rosemary essential oil (REO) in concentrations of 0.0 %, 0.5 %, and 1.5 % v/v, with the aim of evaluating their potential as packaging material for the preservation of fresh cheese, a food characterized by its high moisture and fat content. The films were characterized in terms of structural, morphological, mechanical, physicochemical, antioxidant and antimicrobial properties. FTIR, RAMAN, and SEM analyses confirmed good compatibility among components, while the incorporation of 1.5 % REO improved film elasticity by 12 % and water vapor barrier properties by 75 %. This formulation also showed significant antioxidant activity (50 %) and antimicrobial effects against Staphylococcus aureus and Escherichia coli (the maximum inhibition zones achieving 19.50 ± 0.500 mm). The results of the release kinetics showed sustained release of REO from the chitosan/starch films, fitting the Korsmeyer–Peppas model, indicating a Fickian diffusion mechanism (R 2 = 0.98–0.99). In preservation studies, films containing 1.5 % REO significantly (p < 0.05) extended the shelf life of fresh cheese by effectively reducing weight loss, slowing pH decline, and minimizing color change (L* value) during 12 days of refrigerated storage, compared to both uncoated samples and control films without REO. Overall, results suggest that REO-incorporated chitosan films not only enhance the physical and functional properties of the material but also provide effective protection against oxidation and microbial spoilage. Representing a sustainable and functional alternative for packaging high-moisture, high-fat food products.