Kinetic modeling and characterization of a diffusion-based time-temperature indicator (TTI) for monitoring microbial quality of non-pasteurized angelica juice

• A diffusion based time-temperature-indicator (TTI) was characterized.
• Predictive modeling for diffusion of isopropyl palmitate in TTI was performed.
• Microbial quality and TTI response was monitored for unpasteurized angelica juice.
• Monitoring was done at iso-thermal and dynamic temperatures during storage.
• TTI responded well for predicting aerobic bacterial count in juice during storage.

Time-temperature-indicator, or integrator (TTI), can be used for visual display of food product safety information for consumers. A prototype isopropyl palmitate (IPP) diffusion-based TTI system was characterized and evaluated for monitoring microbial quality of non-pasteurized angelica (NPA) juice based on temperature abuse. Diffusion of IPP in the TTI system was measured at various iso-thermal and dynamic temperatures and a mathematical model based on relationships between diffusion and time-temperature was established. Predicted results from the established model were in good agreement with experimental results. Total aerobe counts in NPA juice reached a critical level of 6 log CFU/mL from an initial load of 3.7 log CFU/mL after 36.6 h and 12.5 h of storage at 15 °C and 25 °C, respectively. IPP diffusion distances were 9.7 mm and 7.2 mm at 15 °C and 25 °C, respectively. IPP diffusion of 7.0 mm in the TTI system was considered to be a threshold point for bacterial quality of NPA juice. However, the proposed TTI was only verified for indicating temperature abuse above 13.5 °C. The TTI system characterized in this study showed potential for monitoring the microbial quality of perishable food products during distribution and storage.