Comparative Analysis of Starch-Based Films Functionalized with Bixa orellana Fruit and Leaf Extracts: A Multiscale Structural, Morphological, and Optical Characterization

This study presents a comparative analysis of starch-based active films functionalized with alcoholic extracts from the fruits (AF) and leaves (AL) of Bixa orellana (2.5–10% w/w), evaluating their structural, morphological, optical, mechanical, barrier, and functional performance. A comprehensive multiscale characterization was performed to analyze the effect of phytochemical composition on structural, morphological, optical, mechanical, barrier, and functional performance. UV-Vis spectroscopy confirmed distinct bioactive profiles: fruit extracts exhibited prominent carotenoid absorption bands (bixin and norbixin, 400–550 nm), whereas leaf extracts displayed characteristic chlorophyll peaks (675 nm) alongside high phenolic/flavonoid content (280–400 nm). This structural differentiation directly influenced material behavior. Opacity measurements at 600 nm demonstrated significant UV-Vis photoprotection, reaching a maximum opacity of 0.435 in 10% AF films. Microscopic analyses by optical microscopy (OM), scanning electron microscopy (SEM), and atomic force microscopy (AFM) revealed that AF integrated smoothly into the starch matrix, reducing surface roughness (RMS = 0.192 μm at 10% AF), whereas AL generated rougher, micro-textured surfaces (RMS = 0.694 μm at 10% AL) due to phase interaction variations. FTIR spectroscopy verified hydrogen bonding and non-covalent molecular interactions between starch chains and functional extract molecules. Mechanically, 10% AF films achieved the highest tensile strength (0.326 ± 0.020 MPa), while 5% AL films provided maximum flexibility (43.49 ± 3.5% elongation at break). Furthermore, AL incorporation significantly improved water resistance, limiting net mass change kinetics to under 50% compared to ~120% in pure starch. Soil-induced mass loss tests showed tunable disintegration kinetics over 28 days, with phenolic-dense formulations exhibiting slower mass loss, although gravimetric measurements cannot distinguish between possible microbial mineralization and physical fragmentation. Antimicrobial agar diffusion assays against Escherichia coli, Staphylococcus aureus, and Candida albicans revealed no clear inhibition zones, indicating that the active hydrophobic compounds remain entrapped within the hydrophilic starch matrix rather than diffusing freely into the agar. Overall, this comparative study highlights the tailored photoprotective, mechanical, and moisture-barrier functionalities achievable using distinct parts of Bixa orellana, presenting a promising pathway for circular, eco-friendly active packaging and medical materials.