Thermal Food Processing

546 Thermal Food Processing: New Technologies and Quality Issues
TABLE 17.8
Effect of Temperature during Pressurizing
at 400 MPa on Pressure Tolerance of E. coli
Temperature
Treatment Time (min)
(°C) 10 15 20 30 40
20 5 a) 5 5 5 5
30 5 5 5 2 0
40 5 5 5 0 0
a) Number of positive growth tube per five test tubes. Initial population
of E. coli was 9.1 × 10 6 CFU/ml.
of the Candida parapsilosis treated at 400 MPa for 10 min survived at 24°C,
whereas only 1% did at 34°C. 30
17.5.3 PRESSURE RESISTANCE OF MICROORGANISMS
Table 17.9 provides the pressure resistance of 14 kinds of microorganisms in a
pressure range of 300 to 500 MPa at 20°C for 20 min. Vibrio parahaemolyticus,
Pseudomonas fluorescens, Acinetobacter sp., and Saccharomyces cereviseae were
killed at 300 MPa, so that the pressurizing condition will kill about 7 log cycles
of these microorganisms at least. This experiment shows that V. parahaemolyticus
is rapidly killed at 1700 atm (172 MPa) at 23°C. 32
Salmonella typhimurium, Morganella morganii, Leuconostoc mesenteroides,
and Candida parapsilosis were inactivated at 400 MPa, and a reduction of at
least 7 log cycles is expected (Table 17.9). It is indicated that S. typhimurium
decreases to less than a 3 log cycle at 3400 atm (344 MPa) for 20 min, 33 and to
a 6 log cycle at 400 MPa at 20°C for 10 min. 34
E. coli and Lactobacillus plantarum survived at 400 MPa but did not at
500 MPa, and therefore, a reduction of at least 7 log cycles is expected (Table 17.9).
E. coli decreases to a 6 log cycle at 400 MPa at 20°C for 10 min. 34
Staphylococcus aureus, Enterococcus faecalis, and Corynebacterium sp. survived
even at 500 MPa (Table 17.9). Previously, it has been shown that S. aureus,
E. faecalis, and Corynebacterium sp. survive even at 600 MPa. 35,36 Therefore, it
will be difficult to kill them at pressure less than 500 MPa and temperature 20°C
for 20 min.
17.6 STERILIZATION OF BACTERIAL SPORES
Inactivation of many kinds of microorganisms by high hydrostatic pressure (HHP)
has been investigated since Hite’s initial research. 8 The HHP is especially known
to be effective in inactivating vegetative cells of various bacteria rather than spores
at room temperature. 11 In order to completely kill the bacterial spores at room