Submitted to: Journal of Food Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/29/2004
Publication Date: 12/8/2004
Citation: Huang, L. 2004. Dynamic measurement and mathematical modeling of the temperature history on hot dog surfaces during vacuum-steam-vacuum processes. Journal of Food Engineering. 71:109-118.
Interpretive Summary: Vacuum-steam-vacuum (VSV) surface pasteurization was recently developed to kill foodborne pathogens such as Listeria monocytogenes attached to many food surfaces. In the past, it was observed that this technology could inactivate a few, but a large number of bacteria still survived the heating. This study developed a high-speed data acquisition system to dynamically measure the surface temperature during VSV processes. The findings of this study provided a fundamental understanding underlying microbial inactivation by VSV processes. A new mathematical model to describe the process was developed, and can be used to optimize this technology, which in turn would lead to manufacturing pathogen-free ready-to-eat foods in the food industry.
Technical Abstract: The objective of this study was to develop a high-speed instrumentation system to measure the surface temperature of hot dogs during VSV processes. A calibrated ultra-fine type-T thermocouple attached to a hot dog surface was used to measure its temperature history. Results indicated that the pressure in the treatment chamber responded immediately and accurately to the events of VSV. The surface temperature history, however, did not instantaneously reach the steam temperature, but followed an exponential trend after saturated steam was flushed into the treatment chamber. A mathematical model was developed to simulate the surface temperature history during steam pasteurization processes. Using this mathematical model to estimate the lethality of VSV processes, it was found that treating with 110°C steam for 0.1 s should have been sufficient to achieve a 5-log reduction in L. innocua inoculated onto the surface of hot dogs, provided that the surface was perfectly smooth and bacteria were all distributed on the surface. The incomplete destruction of bacteria on hot dog surfaces using current VSV processes was explained by the hypothetical theory of capillary condensation. The thermodynamically preferential condensation of steam on and in the capillary pores near the food surface may have prevented the bacteria hidden in the capillary pores from being directly in contact with steam during short steam cycles. This study suggested using a single long steam treatment cycle, instead of multiple short VSV cycles, for a complete destruction of bacteria hidden beneath the surface of ready-to-eat solid foods.