## 1 Introduction
In this case, infrared images (video IRT), thermodynamic laws, and heat exchange mechanisms (convection, conduction, and radiation) were used in order to perform direct, real-time measurements of energy loss from heat from the surface of the sample containing living cells while cooling for 2 min. This technique takes living cell features into consideration and distinguished them from dead or metabolically neutral cells and can be used to count bacteria in water and other fluids. The above research assumes that bacteria's energy production speed increases as a result of their metabolic activity and transformation from complex biochemical compounds into simpler forms [14]. A calorimetric analysis of absolute anaerbo _Cistridium acetobutylicum_ growth confirmed that heat emissions correspond to the microorganisms' cell concentration, so heat emissions should double since the number of microorganisms cells doubled [15]. It is also assumed that the presence of bacteria and their metabolic activity can influence the thermophysical and optic features of the nutrient material, e.g., its emissivity. The positive value of energy (EC) is a result of exothermic reactions and indicates the tested sample's temperature or an increase in temperature with respect to the control sample. The negative value of energy indicates endothermic reactions and a decrease in temperature or emissivity [14]. Thermography as a quick technique for the microorganisms' detection could potentially overcome the limitations of conventional microbiological food-quality assessment methods. It has numerous advantages, such as the following: the fact that it is non-destructive (it can be used to test samples in a non-invasive manner), non-contact measurements that prevent food contamination risk, the possibility of instantaneous temperature measurement for the chosen point, short processing times to obtain a thermal image, the lack of harmful radiation during measurements, and the ease of use and low complexity in tooling. Contrary to other methods, thermal imaging allows for the simultaneous monitoring of large surface (high number of samples at the same time) and temperature changes in real time [9]. However, before it can be commonly used as an online tool for food quality assessment, several limitations must be overcome. The challenge with the mass usage of thermal imaging sensors includes, among others, the need to cool or heat the product in order to increase the temperature's contrast, thermal disturbance from the environment, the heterogenous background of the examined object (as in the case of belt conveyors systems), and the existence of dead pixels in the detector [6]. Other issues that can occur are changeable lightning conditions causing background disturbance that can be observed on the thermograms and the fit of existing algorithms and optimal filter combinations with respect to various kinds of food products. If future research will provide a solution to these problems, the microorganisms' detection using thermal imaging can become a standard procedure ensuring the security of food at mass production scales [1]. This study was an attempt to develop a method for _Bacillus subtilis_ contamination growth monitoring in mortadella using thermal imaging.