Biopolymer-based pH-responsive smart label based on anthocyanin has attracted great attention due to its simple preparation, low-cost, and environmentally-friendly. Freshness indicator label has become a highlighted topic in the field of intelligent food packaging due to their convenience and nondestructive testing. The color changes of pomegranate juice (PJ) at different pH values were studied. Using PJ as an indicator, chitosan and soybean protein isolate (SPI) response labels were prepared. PJ displayed obvious color changes at different pH values. The PJ-chitosan response label showed higher water content and light transmittance than PJ-SPI, and it had an evident color change at different pH values. The chitosan label showed excellent ultraviolet light barrier capacity with the addition of PJ. The PJ-SPI label presented a better pH response compared with the PJ-chitosan label. However, its deformation ability was poor and easy to dissolve. The addition of 30% PJ caused cracks and pores on the surface of the PJ-SPI label. Analysis of Fourier transform infrared spectroscopy (FTIR) confirmed the formation of hydrogen bonds between PJ and chitosan. The images of scanning electron microscopy (SEM) showed the surfaces of PJ-chitosan labels were smooth and flat, and had good compatibility between PJ and chitosan. The two pH-responsive labels had the potential application in shrimp preservation through fresh shrimp preservation. PJ-CS label displayed greater shape stability.
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