Development and characterization of Opuntia-based films for intelligent food packaging

This study focuses on the valorization of Opuntia ficus-indica (OFI) agro-industrial by-products to develop sustainable, intelligent food packaging. The rationale lies in the need to simultaneously reduce agro-industrial waste and replace petroleum-derived packaging materials with bio-based systems capable of providing both food protection and freshness information. Films were formulated by blending pectin extracted from OFI cladodes with commercial citrus pectin (1:1). To introduce colorimetric properties, a betalain-rich extract recovered from prickly pear peels was incorporated (1:1 of polymer). The biopolymer matrix was further optimized using natural montmorillonite (MMT, 2.5% w/w of polymer) as a reinforcing agent and Ca²⁺ (using 2% CaCl 2 w/v solution) for ionic crosslinking. Characterization revealed that the betalain extract improved the UV-Vis light barrier but plasticized the films, while calcium crosslinking and MMT addition counteracted this weakening. The optimized formulation (OFIPC_MMT_100EXT_R) exhibited and enhanced Young’s Modulus to 6.5 MPa, tensile strength to 7.8 MPa, and a densified network with a thickness of 86 µm. This formulation reduced the water vapor permeability values (2.5 × 10⁻¹¹ g/m.s.Pa). Furthermore, the functionalized films demonstrated high sensitivity to ammonia vapors, showing a distinct visual transition from reddish-purple to yellow under alkaline conditions, where the hue angle ( h° ) shifted from 46.7 ° to 100 ° . This colorimetric response can be correlated with the release of volatile spoilage compounds in real matrices, demonstrating the possibility to be used as a real-time visual freshness indicator. These findings highlight a promising strategy for the total valorization of OFI residues into high-added-value materials.