A colorimetric total volatile base nitrogen-responsive film with antibacterial and leaching-resistant properties for accurate tracking fish quality

In this work, an antibacterial, safer, and intelligent film based on dye-loaded rice straw composite was designed for tracking fish freshness. Rice straw was treated with NaOH to graft cations for linking pH-sensitive pigment without separation. Higher concentrations of NaOH removed more hemicellulose, lignin, ash and fat-soluble compounds from rice straw than that of the lower NaOH concentration, improving accessibility to cellulose. NaOH at 10 g/dL changed some of the cellulose crystals from type I to type II. Bromothymol blue molecules (BTBMs) were connected on cationic particles via ionic bonds to obtain porous TVB-N-responsive granules, which were encapsulated in a carboxymethyl cellulose/κ-carrageenan composite to monitor fish freshness. The static attraction and repulsion on BTBMs from cationic rice straw and the anionic polysaccharide composite increased leaching-resistance with a release ratio of 1.76% in 76 g/dL ethanol solution. The smart film had a UVC resistance of 64.48%, a Staphylococcus aureus inhibition rate of 92%, and an optimum TVB-responsive performance. The film turned yellow, green or blue to indicate fish was very fresh, fresh, or close to spoilage, respectively. Our study provides information on the utilization of rice straw and a methodology for the large-scale preparation of smart films for evaluating fish freshness.