Performance of a heating block system designed for studying the heat resistance of bacteria in foods

Abstract

Knowledge of bacteria's heat resistance is essential for developing effective thermal treatments.Choosing an appropriate test method is important to accurately determine bacteria's heat resistances. Although being a major factor to influence the thermo-tolerance of bacteria, the heating rate in samples cannot be controlled in water or oil bath methods due to main dependence on sample's thermal properties. A heating block system (HBS) was designed to regulate the heating rates in liquid, semi-solid and solid foods using a temperature controller. Distilled water, apple juice, mashed potato, almond powder and beef were selected to evaluate the HBS's performance by experiment and computer simulation. The results showed that the heating rates of 1, 5 and 10 °C/min with final set-point temperatures and holding times could be easily and precisely achieved in five selected food materials. A good agreement in sample central temperature profiles was obtained under various heating rates between experiment and simulation. The experimental and simulated results showed that the HBS could provide a sufficiently uniform heating environment in food samples. The effect of heating rate on bacterial thermal resistance was evaluated with the HBS. The system may hold potential applications for rapid and accurate assessments of bacteria's thermo-tolerances.Knowledge of bacteria's heat resistance is of great importance in developing effective food processing methods. Selection of appropriate heating parameters can effectively reduce the target microorganism populations while achieving minimal thermal impacts on food quality. In addition to growth temperatures, stages of growth, bacterial strains, sample compositions, and the pH of the heating medium, heat resistance of bacteria is mainly affected by final temperature, holding time and heating rate 1-3 . Thermal death time (TDT) test is a common method to determine the heat resistance of bacteria 1,[4][5][6][7] . The device used for those TDT tests needs to meet the basic requirements, such as precisely controlled sample temperatures, a short come-up time (CUT) to avoid thermal adaptation of bacteria, and isothermal conditions for uniform sample temperature distributions 5 . Therefore, choosing an appropriate test method is important to obtain accurate determination of bacteria's heat resistance.There have been many studies on TDT test devices in foods. Odlaug et al. 8 used aluminum tubes in a miniature retort system to study thermal destruction of Clostridium botulinum spores in tomato juice. Gaze et al. 9 placed samples of ground meat in 0.5-to 1-mm thick sterile bags, and then immerged them in a shaking water bath. Kotrola et al.10 placed turkey meat samples into a TDT sealed tube heated by a shaking oil bath. Chung et al.11 designed an aluminum test cell heated in oil bath for determining the heat resistance of Clostridium sporogenes in selected foods. There were also studies with capillary tubes using water bath for apple juice 12 , and glass vials with an oven-heated sand bat...

Radio frequency food processing. Current status and perspectives – a review

“…Factors affecting the thermal resistance of microorganisms in radio frequency-heated foods include water activity, proximate composition, pH of the heating medium, growth temperature, microbial strain, growth stage, and are mainly influenced by the final temperature, heating rate, and holding time (Huertas et al 2016;Kou et al 2016;Zhang et al 2021b). Therefore, the rate of RF heating can directly affect microbial survival and food quality (Zhu et al 2017).…”