Air-activation of printed time-temperature integrator: A sandwich package case study

The time-temperature integrator (TTI), a useful colorimetric label indicating food quality, requires a reproducible activation process. A printed TTI was developed that could be stored at room temperature before use and easily air-activated following the opening of the vacuum package. When exposed to air by breaking the package, the TTI color change starts. The TTI reaction system consisted of a colorimetric redox material (leucomethylene blue, leuco-MB), a redox reaction repressor (a mixture of L-ascorbic acid and L-cysteine; AC), and oxygen was supplied from the surroundings, by permeation through a 0.1 mm thick acetate film. The rate of color change from leuco-MB (white) to MB (blue) and the temperature dependency were adjusted by using the different proportions of MB, AC, and glycerol, respectively. The TTI color endpoint, equivalent to the shelf-life of a sandwich (as a case study), and the Arrhenius activation energy (E-a) were finally designed to be the same as those of the sandwich, being 63 hat 5 degrees C and 45.14 kJ/mol, respectively. The experimental and TTI-predicted shelf-life of the sandwich proved to corroborate with the microbial assay results, under dynamic conditions.