Chitosan/Sodium Alginate Composite Intelligent Film Incorporating <i>Campanumoea lancifolia</i> Anthocyanins for Monitoring Shrimp Freshness

This study developed a chitosan (CS)/sodium alginate (SA) composite intelligent film (CA film, CS: SA = 9:1 w/w) incorporating Campanumoea lancifolia anthocyanin (CLA; 0, 10, 15, and 20% w/w based on CA) into the biopolymer matrix for real-time monitoring of shrimp freshness. pH sensitivity experiments showed that CLA exhibited distinct color changes from pH value 1–14, ranging from red (acidic) to yellow (strongly alkaline). Ammonia response tests indicated that CACL15 possessed ideal response sensitivity, capable of changing from red to purple within 30–40 min. Physical property tests showed that with increasing CLA concentration, the tensile strength of the films increased from 29.6 ± 0.21 MPa to 47.4 ± 0.25 MPa, elongation at break increased from 18.5 ± 0.31% to 38.7 ± 0.26%. While moisture content decreased from 17.3 ± 0.15% to 12.1 ± 0.12%. CACL15 formulation was determined to achieve the optimal balance between mechanical strength and indicator sensitivity. In pH/TVB-N tracking experiments of shrimp stored at 4 °C, CACL15 film demonstrated obvious color changes from deep red (day 0) to brown (days 4–6) with the quality changes of shrimp. Highly correlated with the changes in shrimp pH (from 6.96 to 7.91) and total volatile basic nitrogen (TVB-N) values (from 7.7 mg/100 g to 36.87 mg/100 g). Particularly, at the critical spoilage threshold interval where TVBN values transitioned from 15 mg/100 g to 30 mg/100 g, the film’s hue values significantly changed from the red range (338.6–341.4°) to the brown range (10.55–32.63°). Smartphone-based color recognition was further explored as a proof-of-concept approach to objectively quantify the film color change under standardized imaging conditions, which may facilitate intuitive interpretation for end users. The intelligent film developed in this study offers an effective solution for nondestructive, real-time monitoring of seafood freshness, with significant theoretical and application value.