Recycled Cellulose‐Based Colorimetric Indicators for Non‐Contact Detection of Food Contamination

ABSTRACT Sustainable packaging with integrated sensing capabilities is increasingly important for preserving freshness, preventing contamination, and reducing both food and plastic waste. Here, we introduce smart packaging films engineered from recycled cellulose acetate, functionalized with red cabbage–derived anthocyanins. The bio‐composite films demonstrated antioxidant activity (>90% DPPH ^• inhibition) and reversible, well‐defined color transitions under acidic and basic conditions. Remarkably, they also responded to volatile organic compounds (VOCs) released by foodborne pathogenic bacteria, Pseudomonas aeruginosa , Salmonella enterica , Escherichia coli and Staphylococcus aureus , enabling passive, non‐contact identification of contamination through visible optical changes. As a proof of concept, the films visibly changed color after only one day when placed in sealed containers with fresh seafood, reflecting the onset of quality degradation under ambient conditions. This work introduces a sustainable, versatile class of smart packaging that combines active and intelligent functionalities into a single platform, enabling contamination prevention, freshness monitoring, and shelf‐life extension through a simple, visible optical signal. This work demonstrates how recycled cellulose acetate can be transformed into a value‐added material, giving rise to a versatile class of smart packaging that integrates active and intelligent functionalities within a single platform, enabling shelf‐life extension, contamination prevention and freshness monitoring.