Abstract
The pressure-assisted ultra-high temperature (PAUHT) system was built by using soybean oil as pressure-transmitting medium, and the multiple regression equation of soybean oil temperature change (ΔTP) during pressurization as a function of initial temperature (Ti) and set pressure (P) was developed: ΔTP = -13.45 + 0.46 Ti + 0.0799 P - 0.0037 - 2.83 × 10-5 P2. The fitted model indicated that the temperature of the system would achieve ≥121°C at 600 MPa when the initial temperature of soybean oil was ≥84°C. The PAUHT system could effectively inactivate spores of Bacillus subtilis 168 and Clostridium sporogenes PA3679 (less than 1 min). Treatment of 600 MPa and 121°C with no holding time resulted in a 6.75 log reductions of B. subtilis 168 spores, while treatment of 700 MPa and 121°C with pressure holding time of 20 s achieved more than 5 log reductions of C. sporogenes PA3679 spores. By comparing the PAUHT treatment with high pressure or thermal treatment alone, and also studying the effect of compression on spore inactivation during PAUHT treatment, the inactivation mechanism was further discussed and could be concluded as follows: both B. subtilis 168 and C. sporogenes PA3679 spores were triggered to germinate firstly by high pressure, which was enhanced by increased temperature, then the germinated spores were inactivated by heat.
Highlights
Pressure assisted thermal sterilization (PATS), a technique combining high pressure with elevated temperature, has been used to effectively inactivate bacterial spores in low-acid food (Peleg et al, 2008; Nguyen et al, 2010; Olivier et al, 2011)
In this pressure-assistant ultra-high temperature (PAUHT) system, soybean oil was used as the pressure-transmitting medium to get the desired ultrahigh temperature by increasing the initial temperature with compression heating
When the initial temperature of soybean oil was set at 86◦C, the final temperature reached 121◦C with pressure of 600 MPa (Figure 2A)
Summary
Pressure assisted thermal sterilization (PATS), a technique combining high pressure with elevated temperature, has been used to effectively inactivate bacterial spores in low-acid food (Peleg et al, 2008; Nguyen et al, 2010; Olivier et al, 2011). In order to achieve higher temperature during PATS treatment, we supposed that the soybean oil could be used as the pressure-transmitting medium because of its higher compression heating coefficient (9.2◦C/100 MPa) (Patazca et al, 2007; Zhu et al, 2008). This PATS system with higher working temperature could be defined as pressure-assistant ultra-high temperature (PAUHT) system. This system is rarely built and its inactivation effect and mechanism of bacterial spores has never been investigated
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