Time Temperature Indicators (TTI) Based on Chromogenic Bacterium Janthinobacterium sp.

Introduction: The cold chain of perishable food products can often be disrupted by temperature abuse. Time temperature indicators (TTI) or integrators are simple and inexpensive devices that make the continuous monitoring of the time temperature history of chilled products possible throughout the cold chain. Janthinobacterium sp. is a chromogenic bacterium which appears purple during its growth. The time that this bacterium colony appears purple depends on the pH value of the medium where it is cultivated, temperature and atmosphere composition.

Purpose: To develop TTI for food industry based on the chromogenic ability of Janthinobacterium sp.

Methods: Tryptone soy agar (TSA) with pH (HCl) of: 6, 6,5, 7, 8 or 9 was surface-inoculated with 3, 4, 5 or 6 log CFU/cm² of Janthinobacterium sp. and incubated aerobically at 0^°C, 5^°C, 10^°C and 15^°C for 17, 14, 7 and 6 days respectively. Microbiological and pH measurements of TSA were performed during incubation and the growth parameters of Janthinobacterium sp. at different conditions, were estimated using the Baranyi model. In parallel, image analysis was employed in order to explore its potential on estimating microbiological results.  The maximum growth rate (μ_max) was used to determine through the Arrhenius equation the activation energy (E_a) of Janthinobacterium sp. for different pH.

Results: The optimum growth conditions for Janthinobacterium sp. used in the study were 25^°C and pH=7 (under aerobic conditions). Results of microbiological analysis, showed that their population reached the highest levels (9-9.5 log CFU/g) about 72-100h at 15^ο C and 334h at 5^ο C. Significant pH changes (1.5-2.5 units) were observed in TSA samples with initial pH 6 or 6.5. The E_a ranged between 27.84 Kcal/mol (pH: 9) and 21.59 Kcal/mol (pH: 7). The E_a of the microbial growth rate in food ranges from 7.8 to 28.7 Kcal/mol. The endpoint (the time at which a distinct visual color change to the final purple was observed) of the TTI at these pH (9 and 7) when they incubated at 15 °C were 118h and 92h, respectively.

Significance: Such a study could offer a new TTI in the food industry, based on the appearance of purple color of Janthinobacterium sp. as a signal of spoiled food product.