*2.8. Color Response to Ammonia of Bi-Layer Films*

Each of the bi-layer films was placed into the middle-upper layer of a sealed, homemade acrylic box (500 mL). An aqueous ammonia solution was injected into the bottom of each box with 0.1 mL of different concentrations at 0–200 μM, and the color changes

were determined using a CM2300 spectrophotometer [17]. The digital values were also expressed as color changes (Δ*E*).

#### *2.9. Application in Shrimp Freshness Detection of Bi-Layer Films*

According to the determinations of the film results, the A-CBA and A-CBAL2 films were used as shrimp freshness indicators. An amount of 50 g of fresh shrimp was placed inside a sealed packing box (700 mL), whose inner surface was attached to a film at 4 ◦C for 96 h. The color of each film was obtained using a CM2300 spectrophotometer every 12 h. The total volatile basic nitrogen (TVB-N) value was determined according to the method of Zhang et al. [17].
