## 1 Introduction  
The microbiological contamination of food products is a serious issue not only because of the security risk but also because of economic losses related to utilizing unfit food [1]. Conventional techniques are used most often when identifying and quantifying microorganisms. Their applications are laborious, take a lot of time, and most importantly require qualified personnel. Therefore, research is conducted to develop rapid techniques for the microbiological quality analysis of food products [2]. In this regard, innovative methods, including thermal imaging, are becoming more and more popular. The infrared thermography method (IRT) is based on the observation of any object at a temperature above absolute zero (\(-273.15\)\({}^{\circ}\)C) and recording the radiation distribution in the infrared range. Infrared radiation emitted by the tested surface is recorded with a thermal imaging camera, which transforms radiation into an image called a thermogram. The obtained image illustrates temperature distributions on the tested surface. It is presented in the form of colored isotherms, where the points of the same temperature have one color. What is important is that the measurements performed with infrared cameras can be conducted in the dark because the thermogram shows each object that emits infrared radiation [3, 4]. The research using thermal measurements can be divided into two groups: passive and active thermal imaging. In passive imaging, the thermography method-tested object characterizes only the temperature field created during its functioning. In active methods, additional sources of thermal stimulation--heating or cooling--are used. By thermodynamics, both methods of thermal stimulation are equally valuable, with identical powers with respect to the thermal radiation stream. Considering the density of heat streams and the possible obstacles or interruptions, heating is more practical [5]. Initially, thermal imaging was developed for military use. The first research study reporting its usage was limited due to the low sensitivity of thermal imaging systems that were available at that time. With the development of high-resolution digital imaging in analytical tools, thermal imaging measurements started to be used in various domains, such as medicine, material science, fire security [6], veterinary, aviation [7], energetics, construction, metallurgy, and in scientific research on thermodynamic phenomena and heat exchange [8]. Thermal imaging could be also used in the quality assessment of agricultural products and in so-called post-harvest operations. The research contains fruit, vegetables, and meat quality assessment; foreign body detection; cooked food temperature mapping; or packaging flaw detection. Thermal imaging can be also used in all locations that require controlling product temperatures on the production line (e.g., ready-to-eat food production) [9; 7; 10; 11]. While working on a easy, fast, and sensitive microbiological diagnostics technique that could eliminate the preparation and sample modification phase, [PERSON] et al. [12] noticed that all living organisms, including bacteria, produce heat as a result of basic metabolic processes. This emitted thermal energy can be utilized to detect microorganisms using infrared thermography. It was observed that the energy (EC), defined as a ratio of heat created by bacterial metabolism to heat lost, linearly increases with an increase in pathogenic bacteria concentrations (_Vibrio cholerae_, _Vibrio mimicus_, _Proteus mirabilis_, and _Pseudomonas aeruginosa_) [12]. In other research using thermal imaging cameras [13], _Escherichia coli_ bacteria contamination was detected. The results showed 100% effectiveness of the examination and the minimum time required for microbiological contamination detection was 5 h. [PERSON] et al. [14] also realized the potential of thermal imaging techniques with respect to _E. coli_ bacteria quantity indication.