Time‐Temperature Indicator Based on Enzymatic Degradation of Dye‐Loaded Polyhydroxybutyrate

An enzyme activated time‐temperature indicator (TTI) which produces a direct colour change concomitant to variations in integrated time and temperature conditions is described. This direct colour change is realised by degrading a dye‐loaded polyhydroxybutyrate (PHB) film by a depolymerase enzyme. The degradation of the PHB film by the enzyme causes the release of the dye in solution, which in turn undergoes an optical transition from clear to coloured with elapsing time. Macroscopic and microscopic optical observations confirms the uniform distribution of the dye in the PHB film. The dye release kinetics, mediated by the enzymatic reaction, are tested at different temperatures ranging from 4 to 37 °C, and are used to determine the suitability of a dye‐loaded PHB as a time‐temperature indicator for fresh food products based on kinetic parameters previously reported. The kinetic analysis shows that the activation energy of the dye release process is 74 kJ mol−1, and that, at 37 °C, the dye would be totally released within 6 h. However, when incubated at 4 °C, the TTI requires in the range of 168 h (7 days) to release all the dye. These kinetics values highlight the potential of the TTI for monitoring fresh food products that have optimum shelf life around 4 °C. An enzymatic time‐temperature indicator that produces a direct colour change with respect to integrated time and temperature changes in the surroundings is presented. The device consists of a dye‐loaded polymer film (polyhydroxybutyrate, PHB) which is degraded by an enzyme. Upon degradation of the polymer, dye is released into the solution, which becomes coloured with progressing time. Kinetic analysis of the degradation process showed that the activation energy of the system is in a range that is suitable for tracking the freshness of food.