Preparation and characterization of novel natural pigment-indicating film: Application in kiwifruit freshness monitoring.

The marketability of natural pigment-based indicator films is impeded by their weaker color rendering and stability compared with synthetic pigments. Here, we developed novel colorimetric indicators by blending polyvinyl alcohol (PVA) with carboxymethyl cellulose (CMC) and combining alizarin and curcumin. Compared with the individual materials, the PVA and CMC composite films demonstrated superior thermal stability and water resistance. The manufacturing process of these colorimetric indicators was optimized using response surface methodology. The optimum conditions were as follows: PVA at 3.92 g/100 mL; plate pour amount, 48.6 mL; pigment content, 5.8 g/100 mL; pigment ratio, 0.76. The optimized film showed a robust response to CO2 (a color difference of 65.06 ± 2.43). The color difference of the optimized film improved by 98.5 % and 16.86 % for kiwifruit stored at room and low temperatures, respectively. This substantial color change aids in identifying the optimal consumption window for kiwifruit, boosting indicator precision and kiwifruit freshness accuracy.