Fast‐responding thermal‐death‐time tubes for the determination of thermal bacteria inactivation

Abstract

The knowledge of thermal inactivation kinetics, usually expressed in terms of D‐ and z‐values, is of crucial importance for the design of sanitation and sterilization processes. In this study, we designed a simple, fast‐responding, and mechanically stable aluminum tube for inactivation measurements and compared these experiments with the successive‐sampling method at different temperatures. Up to 65°C, we determined a come‐up time of approximately 15 s for the tubes, which is lower than the corresponding values of other devices, presumably because of lower wall thickness, material properties, and a higher surface to volume ratio. D‐values of Escherichia coli calculated from tube inactivation experiments by first‐order kinetics were 370 s (56°C), 126 s (58°C), 53.2 s (60°C), 33.8 s (62°C), and 3.22 s (65°C), and the corresponding values determined with the successive‐sampling flask method were insignificantly different (417, 138, 48.6, and 29.1 s for 56, 58, 60, and 62°C, respectively). These data as well as those measured for Enterobacter cloacae, Pseudomonas putida, Serratia odorifera, and Yersinia rhodei were in close accordance with literature values.

Inactivation kinetics of food-borne pathogens subjected to thermal treatments: a review

“…For example, D-values obtained in 9-mm test tubes were about 8-29 times larger than those obtained using 3-mm capillary tubes for Yersinia enterocolitica strains in physiological saline at 60 C due to non-isothermal test conditions in 9-mm test tubes. Test methods have been developed to eliminate non-isothermal conditions by thermal-death-time capillary tubes and aluminium test cells due to shorter come-up time (the time needed for the sample core temperature to reach the set-point temperature) [50][51][52][53][54].…”

Evaluation of a heating block system for accurate temperature-time controlled pasteurization treatments on various foods

“…Proper design of thermal processes requires comprehensive understanding of thermal impacts on quantitative changes of food quality and thermal resistance of target food-borne pathogens [6][7][8] . Thermal resistance of food-borne pathogens has to be determined under isothermal conditions for developing effective thermal treatments [9,10] .…”

“…For example, D-values of Salmonella at 60°C are different in the same host food because of the different samples size [14,15] . The different thermal resistance of Escherichia coli has been reported owing to using the different test tube materials, such as glass or aluminum [9,16] . Due to the differences in heating principle and mode, the common thermal processes, such as steam, hot air, hot water, radio frequency (RF) and microwave (MW), have different heating rates during thermal treatment [17][18][19] .…”

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

“…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 .…”

“…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.…”