Functional thin films from ultrasound-modified waste-derived pectin for coating applications

Thin film technologies based on renewable sources, as agri-food residues, are attracting increasing interest as sustainable, high-performance materials for advanced coating applications, such as preservation systems for the postharvest industry. This work explored the ultrasound-assisted functionalization of citrus waste pectin as a bio-based material for coating applications. Pectin extracted from orange peel and pomace residues was modified using pulsed high-power ultrasound (2–5 min), and its performance was compared with untreated and commercial pectin references. Ultrasound treatment induced controlled molecular rearrangements, increasing esterification degree and methoxyl content, so converting citrus pectin into a high-methoxyl form without significant degradation. In addition to a 50~60% increase in its antioxidant performance. Uniform modified pectin-based thin films were fabricated by casting, with thicknesses of 50 - 63 µm. The optimized film formulation (F-HPU-MCP-2) exhibited enhanced properties, including a 70% increase in elongation at break, an improved surface barrier with 60% higher WCA, 45% reduction in water solubility, and a complete ultraviolet light shielding. The coating performance was assessed by applying the optimized film-forming solution as edible coatings on fresh strawberries (cold storage). The coating effectively reduced moisture loss in 15~30%, delayed fungal growth, preserved fruit integrity/firmness and colour, extending strawberries shelf-life for up 10 days. These findings demonstrate high-power ultrasound as an efficient green route for tuning the physicochemical and functional properties of waste-derived biopolymers for development of sustainable thin films/coating systems with enhanced functionality.