*3.7. Response Analysis of Indicator Films to Ammonia*

The indicator films exposed to ammonia with different Δ*E* values can be seen in Figure 5B. The colors changed from baby blue to light green and then to yellow green with the increase in ammonia concentration. Moreover, the Δ*E* values were consistent with the visible colors of the films. All of the indicator films had the same variation trend but with some differences. Compared with A-CBAL films, the film with free anthocyanins presented the highest color changes, with an Δ*E* value of 18.29. The encapsulation of anthocyanins decreased their ammonia reactive ability. Even so, the A-CBAL2 film also presented visible color changes with Δ*E* values above 14.28. However, there were slight differences between the films with different liposomes. As a result, a film containing anthocyanin-loaded liposomes also has the potential to serve as a food freshness indicator.

The *Lab* values (A–E), *b* values (F), Δ*E* (G), and color changes of the films (H) with the concentration of ammonia.

#### *3.8. Application on Monitoring Shrimp Freshness of Bi-Layer Indicator Film*

In this study, the A-CBA and A-CBAL2 films were used to monitor shrimp freshness at 4 ◦C. As shown in Figure 6, the Δ*E* of the indicator films and the TVB-N of the shrimp exhibited a similar increasing trend during the storage time. The TVB-N increased to 11.20 mg/100 g and the corresponding Δ*E*<sup>2</sup> was 3.56 for the A-CBAL2 film, with little color change in the first 24 h. Then, the films changed from blue to dark green-yellow with an Δ*E*<sup>2</sup> value of 6.58, and the Δ*E*<sup>1</sup> value of the A-CBA film was 7.63 after 48 h. The *TVB-N* was 27.08 mg/100 g at 48 h. The freshness of shrimp was still approved because the legislation limiting level of *TVB-N* is 30 mg/100 g in Seawater shrimp (GB2733-2015). After 60 h, the *TVB-N* increased to 36.93 mg/100 g, which was spoiled, and the Δ*E* increased dramatically due to the shrimp's deeper putrefaction. The Δ*E*<sup>1</sup> value was 8.96 for the A-CBA film with a deepened yellow color, and the Δ*E*<sup>2</sup> value was 7.83 with a light yellowish color. The color of the film with liposomes was lower than that of the film with free anthocyanin, which may be attributed to the encapsulation of the anthocyanin by liposomes, which reduced the color response sensitivity of the anthocyanin. Meanwhile, the correlation analysis between the Δ*E* of the bi-layer film and the *TVB-N* followed a linear model. For the A-CBA film, the coefficient was 0.8956, and for the A-CBAL2 film, it was 0.9158 (Figure 6B). Therefore, the film with anthocyanin-loaded liposomes can also be used as a good indicator for the detection of the putrefaction period of shrimp.

**Figure 6.** The TVB-N of shrimp and Δ*E* of the films (**A**). Δ*E*<sup>1</sup> is A-CBA and Δ*E*<sup>2</sup> is A-CBAL2 at the storage time. Correlation relation between TVB-N and Δ*E* (**B**). The illustration is the color change of films during storage.
