Influence of Limonene, Ethyl Lactate, and Diethyl Adipate on the Functional Properties of Chitosan-Based Films Loaded with Fumaria officinalis L. Extract and Propolis

Abstract

The development of chitosan (CS)-based films incorporating antioxidant compounds offers a promising approach for the design of functional biobased materials. CS films containing propolis and Fumaria officinalis extract (FOE) were prepared with triglyceryl citrate (TGC) and modified with limonene, ethyl lactate (EL), or diethyl adipate (DEA); their physicochemical, release, and antioxidant properties were evaluated. EL- and DEA-containing films exhibited greater structural homogeneity than limonene-based; higher FOE concentrations increased surface heterogeneity and porosity. Dynamic mechanical analysis showed that the viscoelastic response depended on the additive, with CSEL retaining the highest moduli and CSL-FOE exhibiting the most pronounced softening after FOE/propolis incorporation (G′~105 Pa at 100–110 °C; G″~104 Pa at 120 °C). EL-based films retained the highest tensile resistance and the most balanced strength-deformability profile (stress at break: ~53.58 N/mm2; strain at break: ~14.05%); increasing FOE content reduced stress at break. Film wettability and water uptake were governed by additive and FOE concentration. The release study demonstrated sustained polyphenol delivery, with EL- and DEA-based systems showing approximately 50% release after 24 h. Antioxidant assays confirmed a time- and concentration-dependent increase in activity. The antioxidant response profiles differed among the films, with EL films showing an earlier increase in antioxidant activity, limonene films exhibiting a more gradual response, and DEA films displaying an intermediate response pattern.