Applicability of a microbial Time Temperature Indicator (TTI) for monitoring spoilage of modified atmosphere packed minced meat

The applicability of a microbial Time Temperature Indicator (TTI) prototype, based on the growth and metabolic activity of a Lactobacillus sakei strain developed in a previous study, in monitoring quality of modified atmosphere packed (MAP) minced beef was evaluated at conditions simulating the chill chain. At all storage temperatures examined (0, 5, 10, 15 °C), the results showed that lactic acid bacteria (LAB) were the dominant bacteria and can be used as a good spoilage index of MAP minced beef. The end of product's shelf life as revealed by the sensory evaluation coincided with a LAB population level of 7 log10 CFU/g. For all temperatures tested, the growth of L. sakei in the TTI resembled closely the growth of LAB in the meat product, with similar temperature dependence of the μmax and thus similar activation energy values calculated as 111.90 and 106.90 kJ/mol, for the two systems, respectively. In addition, the end point of TTI colour change coincided with the time of sensory rejection point of the beef product during its storage under isothermal chilled temperature conditions. The estimated activation energy, Eα, values obtained for parameters related to the response of ΔE (total colour change of the TTI) describing the kinetics of colour change of the TTI during isothermal storage (i.e. the maximum specific rate of ΔΕ evolution curve, μΔΕ, and also the reciprocal of ti, time at which half of the maximum ΔΕ is reached), were 112.77 and 127.28 kJ/mol, respectively. Finally, the application of the microbial TTI in monitoring the quality deterioration of MAP minced beef due to spoilage was further evaluated under dynamic conditions of storage, using two separate low temperature periodic changing scenarios, resembling the actual conditions occurring in the distribution chill chain. The results showed that the end point of TTI, after storage at those fluctuating temperature conditions, was noted very close to the end of product's sensorial shelf life. This finding points to the applicability of the developed microbial TTI as a valuable tool for monitoring the quality status during distribution and storage of chilled meat products, which are spoiled by lactic acid bacteria or other bacteria exhibiting similar kinetic responses and spoilage potential.