Phycocyanin as a Natural <scp>pH</scp> ‐Sensor in Biodegradable Films for Smart Food Packaging

ABSTRACT Freshness is a critical factor that heavily influences consumers' decisions when purchasing food products, emphasizing the need for effective methods to visualize and monitor the quality changes in the fresh food supply chain. pH‐sensitive smart films were developed by incorporating phycocyanin into carboxymethyl cellulose and sodium alginate to serve as freshness indicators for food packaging. The colorimetric response of phycocyanin across pH 2–12 demonstrated a distinct color transition from light blue to grayish‐red. To enhance stability, phycocyanin was successfully encapsulated, preserving its functionality within the film matrix, and the phycocyanin incorporated smart films were lyophilized instead of oven drying to preserve the phycocyanin's chromophore, phycocyanobilin . Colorimetric analysis of the films revealed significant color variations, with increasing phycocyanin concentration leading to reduced lightness ( L *). SEM analysis confirmed that phycocyanin incorporation influenced the polymer matrix, resulting in an irregular surface. Increased surface heterogenicity improved water resistance and enhanced hydrophobicity of the films with a increased contact angle of 86.46%. XRD analysis revealed a reduction in film crystallinity from 57.7% to 51.7%, and transparency with increasing concentration, exhibited an amorphous nature due to hydrogen bond formation between the polymer matrix and phycocyanin. FTIR analysis further confirmed the efficient incorporation of phycocyanin into the polymer matrix. All films exhibited antioxidant activity and responded to ammonia exposure with visible color changes, demonstrating their potential as pH‐sensitive films for food freshness sensing. The CMC/SA film incorporated with encapsulated phycocyanin exhibited distinct and progressive color transitions in response to fish spoilage with a Δ E of 23.46 at 0 h to 52.94 by the 48 th hour, confirming that the color change is noticeable, correlating with increased pH and TVB‐N levels. Therefore, it serves as a promising candidate for smart pH‐sensing, enabling nondestructive, real‐time monitoring of fish freshness.