Thermal Food Processing

Pressure-Assisted Thermal Processing 547
TABLE 17.9
Pressure Tolerance of 14 Genera of Bacteria and Fungi
Initial Population Pressure (MPa) a)
Genera (CFU/ml) 300 400 500
Gram negative bacteria
Escherichia coli 1.3 × 10 7 5 b) 5 0
Salmonella typhimurium 3.3 × 10 7 5 0 0
Morganella morganii 2.2 × 10 7 5 0 0
Pseudomonas fluorescens 3.2 × 10 7 0 0 0
Vibrio parahaemolyticus 3.5 × 10 7 0 0 0
Acinetobacter sp. 4.8 × 10 7 0 0 0
Gram positive bacteria
Staphylococcus aureus 8.2 × 10 7 5 5 5
Enterococcus faecalis 5.9 × 10 7 5 5 5
Lactobacillus plantarum 2.4 × 10 7 5 5 0
Leuconostoc mesenteroides 9.4 × 10 7 4 0 0
Corynebacterium sp. 1.1 × 10 7 5 5 5
Fungi
Saccharomyces cereviseae — 0 0 0
Candida parapsilosis 1.0 × 10 7 5 0 0
Neosartorya hiratsukae c) 2.4 × 10 7 5 5 5
a) Pressurization at 20°C for 20 min.
b) Number of positive growth tubes per five.
c) Ascospores.
temperature by pressure, a HHP of over 12,000 atm is required. 9 In addition,
bacterial spores are not inactivated by pressurization at 981 MPa. 37 On the contrary,
it has also been established that HHP is able to inactivate bacterial spores
more effectively when combined with temperature. 5,12,22,23,38–42 Even though the
temperature is relatively low (below 60°C), the death rate changes considerably,
and the inactivation behavior of spores by pressurization is different from that of
spores by heating alone. 5,26,39−42 Thus, it is important to clarify kinetically the
inactivation behavior of various kinds of bacterial spores due to the function of
temperature and pressure. However, though there have been some investigations
carried out at temperatures lower than 100°C, 38–42 studies above 100°C are rare. 23
The inactivation behavior of bacterial spores by thermal treatment combined
with HHP has been studied, in which the temperature range is from 25 to 120°C. 1,2,4
The heat-resistant microorganisms used were Bacillus subtilis, Bacillus coagulans,
Bacillus stearothermophilus, and Clostridium sporogenes (PA3679), which occasionally
cause rancidity of pasteurized and sterilized foods. These results are introduced
in this section.