Structure-Forming Potential of Plant Components in the Reformulation of Composite Films Produced from Citrus Pectin...

This study investigated the rheological, structural, barrier, mechanical, optical, and thermal properties of composite edible films based on citrus pectin and vegetable purées derived from broccoli, cauliflower, pumpkin, carrot, and their blends. Film-forming formulations were characterized in terms of rheological behavior, thickness, microstructure, gas and water vapor permeability, optical and mechanical properties, water contact angle, and thermal stability. The incorporation of vegetable purées significantly modified the properties of the pectin-based matrices. All film-forming solutions exhibited non-Newtonian shear-thinning behavior, with flow behavior index values below unity. The addition of vegetable purées markedly increased viscosity and flow resistance, indicating the formation of more structured systems with stronger intermolecular interactions. Apparent viscosity increased from 0.19 Pa·s in the control sample to 1.41 Pa·s and 1.19 Pa·s in the broccoli (B) and broccoli-cauliflower (B-CF) formulations, respectively, while the consistency coefficient increased from 0.29 to 51.38 Pa·sⁿ. Composite films exhibited lower water contents (0.090-0.114 gH₂O·g_d.m.^-1) than the control film (0.179 gH₂O·g_d.m.^-1) and were thicker (170-282 μm) than the pure pectin film (125 μm). Barrier analysis revealed a reduction in water vapor permeability from 18.99·10^-10 to 10.74-14.69·10^-10 g·m^-1·s^-1·Pa^-1 and a decrease in carbon dioxide permeability from 21.95 to 10.47-17.91 GRT. The carrot-containing film exhibited the highest tensile strength (62.17 MPa), whereas the pumpkin-carrot film demonstrated the most favorable combination of barrier and mechanical properties, including the lowest oxygen permeability (6.95 GRT), low water vapor permeability (10.74·10^-10 g·m^-1·s^-1·Pa^-1), and high tensile strength (51.02 MPa). Thermogravimetric analysis revealed similar three-stage degradation profiles for all samples, while vegetable incorporation modified moisture release and increased residual mass. The obtained results confirmed the research hypothesis that vegetable-processing by-products can serve as valuable structure-forming components of pectin-based composite films and that interactions between vegetable-derived biopolymers and citrus pectin improve the mechanical, barrier, and functional properties of the resulting materials. Among the tested formulations, the pumpkin-carrot film demonstrated the greatest potential for further development as a biodegradable packaging material. The utilization of vegetable by-products in pectin-based films represents a sustainable approach supporting circular economy principles and the development of environmentally friendly packaging systems.