Abstract
Sterilizing is extremely vital in food processing, where its effect is supposed to be calculated from the sterilizing temperature and time at the holding tube. However, flow behavior of direct steam injection heating inside the holding tube after the injection nozzle has been unclear, creating serious uncertainty as for the sterilization effect, leading to major risk in food processing. This study was essentially conducted to market sterilized foods by steam injection heating in the U.S.A. This article includes useful experimental and calculational results concerning the mixing length of steam and liquid foods in the holding tube to obtain the sterilizing effect accurately. As for experiment, the holding tube was made of transparent Teflon. Laser Doppler Velocimetry was used to measure the mixing length and velocity distribution in the tube. Measurements of the mixing length were successfully made, despite the extremely short time phenomena. CFD by Euler’s multiphase flow model to calculating the mixing length, the velocity and temperature distributions in the holding tube have been also considered to compare with the experiment. This part, or the mixing section, does not possess functionality as the sterilizing tube. Based on these experiment and calculation, the mixing length for a single nozzle type has become clearly obtained. As temperature distribution measured is also taken into consideration, a good estimation of real sterilizing effect can be made. An excellent consistency exists between sterilizing effect calculated based on these results and the thermal death rate of Clostridium Sporogenes inoculated in soybean milk in the sterilizers. Based on the temperature and holding time obtained from this study, the actual sterilizing effect can be now calculated without risk of a too small or an excessive margin of safety. Sterilizing condition based on these results was accepted by the FDA.
