Abstract:In order to develop an indicator film that is both pH-sensitive and antibacterial for monitoring the freshness of chilled mutoon, purple sweet potato extract microcapsules (PEM) were prepared. Using sodium alginate and low-acyl gellan gum (SAL) as the base material, with Ag NPs and microcapsules as enhancers. The effects of indicator films (SAL, SAL/Ag NPs, SAL/Ag NPs/PEM) were explored and applied to the monitoring of mutoon freshness. The results indicated that the wall material of PEM had a good encapsulation effect, enhancing the thermal stability of the core material and providing certain antioxidant capabilities. The addition of Ag NPs and PEM improved the mechanical properties, barrier properties, thermal stability, and antioxidant capacity of the single SAL film;specifically, SAL/Ag NPs/PEM2 exhibited the highest tensile strength (12.21MPa) and the lowest oxygen permeability (7.25g·mm/（m2·d）), with a compact and orderly cross-section. X-ray diffraction analysis showed that the crystallinity of Ag NPs was good, with distinct and sharp diffraction peaks, which remained unaffected when mixed with PEM. Fourier-transform infrared spectroscopy analysis indicated that the structures of the components of the indicator film were similar and had good compatibility. When the film was exposed to ammonia gas, its color underwent significant changes, gradually shifting from purple to green and finally to blue. Utilizing this property, the freshness of mutoon stored at 4℃ was monitored. Experimental results demonstrated that on the 4th and 8th days, the mutoon reached secondary freshness and decay states, respectively, corresponding to color changes in the indicator film SAL/Ag NPs/PEM2 from purple to green and blue. In summary, SAL/Ag NPs/PEM2 was highly sensitive to changes in mutoon freshness and can be used for monitoring its freshness.
