Adjustment of Arrhenius activation energy of laccase-based time–temperature integrator (TTI) using sodium azide

When devising a time–temperature integrator (TTI), a chromatic color change indicator, Arrhenius activation energy (Ea) of TTI needs to coincide with that of the food in TTI packages. In this study, a new method of adjusting Ea of laccase-based TTI was developed by using NaN3 known to have a true inhibitory effect on laccase. An enzymatic prototype TTI was produced with laccase and formulated to have affordable reaction stability. NaN3 was treated in different concentrations and its effect on altering Ea was tested. A relationship between Ea of TTI vs. NaN3 concentration was established, and based on this relationship, the necessary amount of NaN3 to provide the laccase TTI for having the same Ea as was a given Ea of Pseudomonas fragi growth as a microbiological quality of model food was determined. Through storage tests, it turned out that the customized TTI with the Ea same as that of the model food could accurately predict the microbiological levels as compared to the TTI with lower or higher Ea. Consequently, the method of adjusting laccase-based TTI Ea with NaN3 added was found to be beneficial to design TTI fit for a particular food in TTI packages.