Preparation of fish freshness colorimetric indicator label based on the dye of BTB grafted on MOF carrier

This work introduces a potential fish freshness indicator film based on cellulose acetate (CA) and polyethylene glycol 4000 (PEG 4000) incorporated with a novel dye of bromothymol blue (BTB) grafted on MOF (Cr-MIL-101-NH2) carrier. The characterization results of the modified dye (MOF-BTB) infer that most of the BTB is integrated with the framework by intermolecular force without breaking the MOF structure. The colorimetric film's oxygen transmission, water vapor transmission, and elongation at break, after the addition of MOF-BTB, shows a decrease, while the tensile strength of the film increase. The MOF-BTB film has observed no BTB migration in the simulated food liquid of neutral, acidic, and alcoholic food; besides, it preserves the color-change ability and is more profound and stable than the BTB film with the same effective dye content. We use the prepared freshness label for Grass carp freshness monitoring under 25 ℃. The freshness label produces a noticeable color change consistent with the fish spoilage around the total volatile basic nitrogen (TVB-N) threshold, which can warn the spoil of the fish. Therefore, the developed colorimetric freshness label can track fish freshness visually and non-destructively using synthetic dye without worrying about contaminating the fish from migration.