Anthocyanin/curcumin intelligent films with high pH sensitivity for freshness maintenance and real-time monitoring of dried tofu

Intelligent packaging materials offer innovative solutions for the freshness monitoring and quality maintenance of high-protein foods during their preservation and distribution. However, most existing intelligent packaging films rely on single natural pigments or synthetic indicators, which suffer from narrow color-changing ranges or safety controversies, while their biodegradability is largely overlooked. To this end, the present study prepared composite films comprising soy hull nanocellulose, polyvinyl alcohol, and pullulan, into which purple cabbage anthocyanin (PCA), curcumin (CU), and their blends at different ratios (PCA:CU = 8:2, 5:5, and 2:8 v/v) were incorporated. Results indicated that PCA and CU formed a hydrogen bond network with the film matrix via phenolic hydroxyl groups, significantly enhancing the mechanical properties of the composite films (P < 0.05). The incorporation of PCA and CU also improved thermal stability and hydrophobicity while reducing water vapor permeability. Among the formulations, PCA/CU-3 (8:2 v/v) exhibited optimal overall performance, showing the most distinct color response across pH 4–12, an antibacterial rate of 93.87% against Pseudomonas fragi , and effective delay of microbial growth and total volatile basic nitrogen (TVB-N) accumulation in dried tofu, extending its shelf life to 12 days. The film color gradually changed from deep red to deep purple during spoilage, enabling visual monitoring. Additionally, PCA/CU-3 degraded noticeably within 25 days under soil-burial conditions. Overall, this study demonstrates a novel degradable food-packaging material integrating antibacterial preservation and real-time spoilage monitoring functions.