Development of a microbial Time Temperature Indicator for monitoring the shelf life of meat

Time Temperature Indicators (TTIs) constitute smart devices through which the full history of the time-temperature profile of a food is monitored. The objective of the current study was to develop a versatile microbial TTI based on the violacein formation, a violet pigment produced by the microorganism Janthinobacterium sp. during early growth, depending on temperature and intrinsic properties of the growth medium. The TTI system consisted of Tryptic Soy Agar enriched with 1% glycerol, spot-inoculated with the bacterium. Input parameters were the storage temperature, the pH of the medium, the initial concentration of the microorganism and the volume of the spot. Image analysis was used to estimate the color change of the spots. Luminosity (L*) parameter described the color change adequately. The Baranyi model was used to fit the violacein kinetics data (L* curve) estimating the TTI's endpoint, i.e., the time at which the violet color occurred. Survival analysis was used to analyze the endpoint data assessing the activation energy, E-a(TTI), and the TTI's endpoint at a reference temperature (t(endpoint)(TTI,ref)). The E-a(TTI) and t(endpoint)(TTI,ref) (T-ref = 0 degrees C) parameters ranged between 65.1-110.3 kJ/mol and 10.1-107.6, respectively. Based on the estimated E-a(TTI) and t(endpoint)(TTI,ref) parameters, a decision can be made on the most suitable combination of pH, initial concentration and spot quantity for monitoring the impact of time temperature profile of different foods on the occurrence of spoilage. The TTI was validated for spoilage of minced beef meat under isothermal and dynamic storage conditions using data generated in this study. The applicability of the TTI was also evaluated to other meat products, including vacuum packaged cooked meat products, using literature data.