Optimization and characterization of colorimetric composite film based on biodegradable polymers (Gluten and Carboxymethyl Cellulose) and Roselle (Hibiscus Sabdariffa) anthocyanins as a TVN-B indicator in fish fillet

Colorimetric indicators are essential in intelligent packaging for food freshness monitoring. This study utilized Hibiscus sabdariffa extract as a colorimetric indicator, confirming the presence of anthocyanins, phenols, flavonoids, and antioxidant activity. Anthocyanins displayed color changes from red to blue and yellow as pH increased from 2 to 12. The effects of anthocyanin (10–30% w/w) on the physical properties of gluten (1–3% w/w) and CMC (0.5–1.5% w/w) composite films were analyzed using response surface methodology (RSM). The addition of anthocyanins increased film thickness, tensile strength, and modulus of elasticity while decreasing elongation at break (p < 0.05). Higher anthocyanin levels (30%v/w) reduced moisture content and increased solubility. All three variables significantly lowered water vapor permeability (p < 0.05). Redness (a*) was influenced by anthocyanin, gluten, and the interaction of CMC × anthocyanin, while the yellowness index (1.85 to 2.93) increased with more gluten and anthocyanin. The optimal composition—3% gluten, 1.5% CMC, and 10% anthocyanin—offered the highest thermal stability. FT-IR and SEM confirmed the successful incorporation and compatibility of anthocyanins within the film. XRD showed that anthocyanins did not affect film crystallinity. These gluten/CMC films with Hibiscus sabdariffa indicator exhibited significant color changes in fish fillets, aligning with TVB-N variations andDifferent colorimetric indicators are employed for various intelligent packaging applications depending on the product type effectively indicating spoilage.

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