Hypothesis: Developing bio-based smart packaging for non-destructive monitoring of food freshness requires designing colorimetric systems with high stability and sensitivity toward volatile spoilage compounds. In this regard, curcumin encapsulated within Pluronic nanomicelles and stabilized in a carboxymethyl cellulose (CMC) matrix is introduced as a smart food packaging system capable of detecting ammonia vapor colorimetrically and non-destructively monitoring food spoilage.
Methods: Bio-based films containing nanocurcumin were fabricated via solution casting, and their structural, mechanical, and antioxidant properties were studied using XRD, FTIR, FESEM, tensile testing, and DPPH assays. Then, the colorimetric response of the films to different concentrations of ammonia vapor was investigated through visual observation, UV-Vis spectroscopy, and CIELab color space analysis. Finally, the performance of the selected film in non-destructive monitoring of fish freshness during storage at ambient and refrigerated temperatures was evaluated based on changes in pH, total volatile basic nitrogen (TVB-N), and total color difference (?E).
Findings: The results showed that nanocurcumin was successfully stabilized in the polymer matrix and significantly increased the antioxidant activity of the films, although increasing its concentration was accompanied by a decrease in mechanical properties. Considering the balance between mechanical strength and antioxidant activity, the CMC-CIT-CUR2 film (containing 2 wt.% nanocurcumin) was selected as the optimal sample. Upon exposure to ammonia vapor, this film showed a distinct color change from yellow to orange and then dark red, and UV-Vis and CIELab analyses confirmed its suitable sensitivity. In the fish freshness monitoring test, the film's color changes showed a favorable correlation with increases in pH and TVB-N under both storage conditions, which demonstrates its real-time spoilage detection capability. Overall, the developed colorimetric film, as a bio-based and sensitive system, has high potential for application in smart packaging and freshness monitoring of fishery products.