Development of Pullulan-Based Colorimetric Film with Butterfly Pea for Shrimp Freshness Monitoring

Colorimetric indicators based on biopolymers and natural colorants represent a promising approach for modern food freshness monitoring systems. In this study, colorimetric films based on pullulan with 2% and 4% butterfly pea flower (BPF) powder were fabricated and evaluated for their physical and optical properties. Furthermore, visual and colorimetric analyses of the films color changes in response to pH and ammonia were also performed. Finally, film with 4% of BPF were tested as a freshness-monitoring label during shrimp storage. The results showed that BPF incorporation did not significantly affect film thickness, but it increased film opacity and improved UV and visible-light barrier properties. The incorporation of BPF also altered and intensified the color of the pullulan films. The films exhibited a distinct response to pH changes, with their color changing from red under strongly acidic conditions, through purple and blue, to olive green under alkaline conditions. Moreover, the films responded to ammonia, exhibiting a visually perceptible color change from blue to green. The colorimetric film containing 4% BPF exhibited visually distinct color changes associated with shrimp spoilage, indicating its potential as a freshness-monitoring label during refrigerated storage.