Chitosan/cassava starch films incorporated with purple sweet potato anthocyanin for pH-responsive pork freshness monitoring.

This study developed a pH-responsive film using purple sweet potato anthocyanin (PSPA) as an indicator and a chitosan (CH)/cassava starch (CS) blend as the film-forming matrix for real-time monitoring of pork freshness at 25 °C and 4 °C. Incorporation of 0.03% PSPA enabled the film to maintain high color responsiveness while improving mechanical performance, with tensile strength (41.50 MPa) and elongation at break (23.85%) increasing by 47.6% and 92.3%, respectively, compared to the control film. Instrumental analysis confirmed that PSPA was dispersed amorphously within the CH/CS matrix, and hydrogen bonds were formed among the three components, enhancing the structural compactness and reducing the crystallinity of the film. Molecular docking and density functional theory calculations were innovatively employed to visualize the molecular interactions between PSPA and the CH/CS matrix. Results revealed that hydrogen bonding and van der Waals interactions formed among the three components under pH 4.4, which was further corroborated by molecular dynamics simulations. These findings provide a theoretical basis for the improved mechanical properties and structural compactness of the film. In pork freshness monitoring over both 30 h at 25 °C and 9 d at 4 °C, the film exhibited distinct colorimetric changes from blue to gray-green and finally to yellowish-brown (ΔE > 5), accurately corresponding to the fresh, sub-fresh, and spoiled states of the pork. This work established a multi-scale relationship from molecular interactions to microstructure and ultimately to macroscopic film properties, providing new insights for designing anthocyanin-loaded polysaccharide-based smart packaging from the perspective of molecular interaction mechanisms.