Development of shrimp freshness indicating films by immobilizing red pitaya betacyanins and titanium dioxide nanoparticles in polysaccharide-based double-layer matrix

Double-layer film was prepared by immobilizing red pitaya betacyanins and titanium dioxide nanoparticles in locust bean gum/polyvinyl alcohol and agar/polyvinyl alcohol film matrices, respectively. Locust bean gum/polyvinyl alcohol film matrix containing red pitaya betacyanins was used as the sensing layer, while agar/polyvinyl alcohol film matrix containing titanium dioxide nanoparticles was used as the protective layer. The properties of double-layer film were measured and the film was used to indicate shrimp freshness. The double-layer film showed a thickness of 0.145 mm, water vapor permeability of 13.04 × 10−11 g m−1 s−1 Pa−1 and tensile strength of 40.49 MPa. Meanwhile, the double-layer film had strong UV–Vis light barrier ability and free radical scavenging ability (28.23% at 5 mg/mL). When the double-layer film was exposed to alkaline solutions and ammonia atmosphere, it changed from initial red-violet to brown/yellow. The double-layer film showed good color stability during storage at 4 °C for 48 days. Notably, the double-layer film effectively indicated the spoilage of shrimp by changing film color from red-violet to pink. This study suggested the double-layer film had good color stability and a great potential in the smart packaging.