pH-responsive film from Galla chinensis residue/chitosan with lac dye for shrimp freshness monitoring

Smart packaging films based on biomass-derived matrices and bioactive indicators enable real-time monitoring of food freshness and extend shelf life. In this study, <i>Galla chinensis</i> residue nanoparticles prepared by colloid milling were incorporated into chitosan to enhance its barrier and mechanical properties. Natural lac dye was introduced as a pH-sensitive indicator for shrimp freshness monitoring. The nanoparticles eliminated UV transmittance at 280 nm (from 70.16 % to 0 %), reduced water vapor permeability (from 0.68 to 0.53 (g·mm)·(kPa·h·m²)^-1), increased tensile strength (from 14.9 to 23.3 MPa), and improved antioxidant activities (ABTS from 12.92 % to 59.32 %, DPPH from 2.43 % to 56.29 %) and antibacterial efficiency (> 99.9 %). The film extended shrimp shelf life by 2 days at 4 °C and exhibited distinct color changes correlated with spoilage, attributed to pH-responsive structural transformations of lac dye molecules. This research demonstrates a sustainable, waste-valorizing strategy for developing multifunctional smart packaging films.