Development of Guar Gum/Chitosan/Polyvinylpyrrolidone Smart Films Containing Purple Sweet Potato Extract for the Real-Time Monitoring of Shrimp Freshness

A biodegradable, antioxidant smart film was prepared using a solution casting method. Anthocyanins in purple sweet potato extract (PSPE) were added to guar gum (GG), chitosan, and polyvinylpyrrolidone matrices as antioxidants and smart pH indicators to determine the freshness of meat products. The resulting GCPP films were characterized, and the mechanical, antibacterial, and antioxidant properties of the films were measured. Cytotoxicity assays confirmed the nontoxic nature of the material, complying with food contact material standards. Furthermore, shrimp freshness monitoring tests validated its practical application potential. As the basic skeleton of the smart film, GG endowed toughness and ductility. Minimal amounts of PSPE were evenly distributed in the film, forming hydrogen bonds with the matrix molecules, and the cross-section of the smart film was smooth and continuous. PSPE improved matrix compatibility and minimally affected the hydrophilicity of the film. As the PSPE content increased, the opacity of the GCPP film increased from 3.91 ± 0.01 to 4.30 ± 0.05, and the UV-blocking rate increased from 61.10% to 99.99%. The elongation at break increased from 24.44% to 38.26%, while the tensile strength decreased from 41.71 ± 3.22 MPa to 35.42 ± 1.84 MPa. Moreover, the GCPP film was highly sensitive to pH changes. For example, in the shrimp freshness test, the GCPP film changed from meat-pink to brownish-yellow when the volatile base nitrogen was 18.24 mg/100 g. Therefore, this study provides an effective method to prepare smart films that are environmentally friendly indicators of food freshness.