Biodegradable films based on avocado seed starch and essential oils from mandarin peel (Citrus unshiu Marcow. cv. Miyagawa Wase) and rosemary (Rosmarinus officinalis)

This study evaluated biodegradable films based on avocado seed starch incorporated with mandarin peel and rosemary essential oils, both in their free forms (MEO, REO) and microencapsulated forms (MEM, REM), to compare their effects on the mechanical, thermal, structural, and optical properties of the material. Films containing microencapsulated oils exhibited greater thickness, reaching 0.130 mm in REM, whereas MEO showed the highest tensile strength (3.3 MPa ) and elastic modulus (19.58 MPa), indicating greater rigidity. In contrast, REM achieved the highest elongation at break (30.62 %), reflecting greater flexibility. Differential scanning calorimetry (DSC) revealed an endothermic transition for MEM at 155.28°C, with an enthalpy of −126.88 mJ, whereas REM displayed a more stable profile without pronounced thermal events. FTIR spectra exhibited characteristic bands at 3272–3281 cm⁻¹ (O–H) and 1654–1633 cm⁻¹ (C=O), which were more intense in films with encapsulated oils, suggesting molecular interactions between the active components and the polymer matrix. SEM micrographs revealed rougher and more heterogeneous surfaces in REM and MEM, in contrast to the smoother structures observed in ROE and MEO. Regarding optical properties, REM showed the highest color difference (ΔE = 10.6), while MEM exhibited the highest transparency (5.04 %). Overall, microencapsulation enhanced the thermal, structural, and functional stability of the essential oils, representing an effective strategy for developing active biodegradable packaging suitable for the food industry. Graphical abstract of the physicochemical characterization of mandarin peel and rosemary essential oil microcapsules, and their application in biodegradable films.