Other Food Protection Methods
461
275 for Y. enterocolitica
350 for Salmonella serotype Typhimurium
375 for L. monocytogenes
450 for Salmonella serotype Enteritidis
700 for Staphylococcus aureus
700 for Escherichia coli 0157:H7
The effectiveness of HHP against V. parahaemolyticus was demonstrated by Styles et al.
58 who found
that 170 MPa at 23
◦ C for 10 minutes would inactivate about 10
6 cells/ml in clam juice. On the other
hand, 340 MPa in 80 minutes at 23
◦ C was required to inactivate about 10
6 cfu/ml of L. monocytogenes
in ultrahigh temperature (UHT) milk.
When whole (3.5% fat) and skim (0.3% fat) milk were subjected to 400 MPa at 25
◦ C for 30 minutes,
shelf life was extended to 45 days at refrigerator temperatures while the untreated milk had a shelf
life of 15 days.
13 However, since plasmin was not inactivated, casein hydrolysis occurred, leading to
flavor defects upon prolonged storage. In another study, combining HHP and mild heating was shown
to be very effective in destroying E. coli 0157:H7 and S. aureus.
41 In UHT whole milk or poultry
meat, each treated with 400 MPa at 50
◦ C for 15 minutes, E. coli 0157:H7 showed a 6-log reduction in
poultry and a 5-log reduction in the milk compared to <1-log reduction for a treatment of 400 MPa
at 20
◦ C. Interestingly, S. aureus was inactivated more efficiently in milk than in the poultry meat.
The effect of HPP on Vibrio species was studied by Berlin et al.
5 who found that 250 MPa for 15
minutes or 300 MPa for 5 minutes at 25
◦ C reduced a mixture of five species to nondetectable levels.
The species and strains included were V. parahaemolyticus, V. vulnificus, V. cholerae 01 and non-01,
V. hollisae, and V. mimicus. Using oysters, V. parahaemolyticus at a level up to 8.1 × 10
7 cfu/g or V.
vulnificus at up to 2.5 × 10
7 cfu/g were reduced to <10 cfu/g with 200 MPa for 10 minutes at 25
◦ C.
The microbiota of vegetables was essentially unaffected by 100 and 200 MPa treatments at 20
◦ C for
10 minutes or 10
◦ C for 20 minutes, but at 300 MPa significant reductions occurred.
4 Saccharomyces
cerevisiae was effectively reduced by 300 MPa at 10
◦ C for 20 minutes while 350 MPa was needed to
reduce most Gram-negative bacteria and molds. The Gram positives were not completely reduced with
400 MPa. However, these investigators noted some undesirable changes in vegetables with pressures
>300 MPa. For example, the skin of tomatoes loosened and peeled away, and lettuce, while remaining
firm, underwent browning. In another study, spinach leaves lost nutrients after treatment at 400 MPa
for 30 minutes at 5
◦ C, while cauliflower was more acceptable under the same conditions.
47 Thus,
some fresh vegetables appear to be unsuitable for HHP preservation treatments.
CO 2 under high pressure is considerably more antimicrobial than under atmospheric conditions. In
one study, CO 2 at 6.18 MPa for 2 hours reduced about 10
9 cfu/ml of L. monocytogenes to undetectable
levels in distilled water or broth, while N 2 under the same condition did not.
60 At 13.7 MPa, CO 2
was effective against L. monocytogenes and Salmonella serotype Typhimurium in chicken meat, egg
yolk, shrimp, and orange juice. In another study, the concentration of dissolved CO 2 was increased
by using microbubbles of pressured CO 2 . At 6 MPa, 35
◦ C, and a residence time of 15 minutes,
the following results were achieved.
54 : Lactobacillus brevis was completed inhibited at ≥11γ (γ =
Kuenen’s gas absorption coefficient); E. coli and Saccharomyces cerevisiae were inhibited at ≥17;
Torulopsis versatilis required ≥21; and Z. rouxii could be sterilized at 10 MPa and 26. The greater
resistance of Z. rouxii compared to T. versatilis and S. cerevisiae is shown in Figure 19–3.
Encapsulated viruses such as cytomegalovirus and herpes simplex type 1 have been found to be
inactivated at 300 MPa and 25
◦ C for 10 minutes. The pressure appears to damage the viral capsule
and prevent the binding of viral particles to host cells. On the other hand, sindbis virus resisted 700
MPa.
8
461
275 for Y. enterocolitica
350 for Salmonella serotype Typhimurium
375 for L. monocytogenes
450 for Salmonella serotype Enteritidis
700 for Staphylococcus aureus
700 for Escherichia coli 0157:H7
The effectiveness of HHP against V. parahaemolyticus was demonstrated by Styles et al.
58 who found
that 170 MPa at 23
◦ C for 10 minutes would inactivate about 10
6 cells/ml in clam juice. On the other
hand, 340 MPa in 80 minutes at 23
◦ C was required to inactivate about 10
6 cfu/ml of L. monocytogenes
in ultrahigh temperature (UHT) milk.
When whole (3.5% fat) and skim (0.3% fat) milk were subjected to 400 MPa at 25
◦ C for 30 minutes,
shelf life was extended to 45 days at refrigerator temperatures while the untreated milk had a shelf
life of 15 days.
13 However, since plasmin was not inactivated, casein hydrolysis occurred, leading to
flavor defects upon prolonged storage. In another study, combining HHP and mild heating was shown
to be very effective in destroying E. coli 0157:H7 and S. aureus.
41 In UHT whole milk or poultry
meat, each treated with 400 MPa at 50
◦ C for 15 minutes, E. coli 0157:H7 showed a 6-log reduction in
poultry and a 5-log reduction in the milk compared to <1-log reduction for a treatment of 400 MPa
at 20
◦ C. Interestingly, S. aureus was inactivated more efficiently in milk than in the poultry meat.
The effect of HPP on Vibrio species was studied by Berlin et al.
5 who found that 250 MPa for 15
minutes or 300 MPa for 5 minutes at 25
◦ C reduced a mixture of five species to nondetectable levels.
The species and strains included were V. parahaemolyticus, V. vulnificus, V. cholerae 01 and non-01,
V. hollisae, and V. mimicus. Using oysters, V. parahaemolyticus at a level up to 8.1 × 10
7 cfu/g or V.
vulnificus at up to 2.5 × 10
7 cfu/g were reduced to <10 cfu/g with 200 MPa for 10 minutes at 25
◦ C.
The microbiota of vegetables was essentially unaffected by 100 and 200 MPa treatments at 20
◦ C for
10 minutes or 10
◦ C for 20 minutes, but at 300 MPa significant reductions occurred.
4 Saccharomyces
cerevisiae was effectively reduced by 300 MPa at 10
◦ C for 20 minutes while 350 MPa was needed to
reduce most Gram-negative bacteria and molds. The Gram positives were not completely reduced with
400 MPa. However, these investigators noted some undesirable changes in vegetables with pressures
>300 MPa. For example, the skin of tomatoes loosened and peeled away, and lettuce, while remaining
firm, underwent browning. In another study, spinach leaves lost nutrients after treatment at 400 MPa
for 30 minutes at 5
◦ C, while cauliflower was more acceptable under the same conditions.
47 Thus,
some fresh vegetables appear to be unsuitable for HHP preservation treatments.
CO 2 under high pressure is considerably more antimicrobial than under atmospheric conditions. In
one study, CO 2 at 6.18 MPa for 2 hours reduced about 10
9 cfu/ml of L. monocytogenes to undetectable
levels in distilled water or broth, while N 2 under the same condition did not.
60 At 13.7 MPa, CO 2
was effective against L. monocytogenes and Salmonella serotype Typhimurium in chicken meat, egg
yolk, shrimp, and orange juice. In another study, the concentration of dissolved CO 2 was increased
by using microbubbles of pressured CO 2 . At 6 MPa, 35
◦ C, and a residence time of 15 minutes,
the following results were achieved.
54 : Lactobacillus brevis was completed inhibited at ≥11γ (γ =
Kuenen’s gas absorption coefficient); E. coli and Saccharomyces cerevisiae were inhibited at ≥17;
Torulopsis versatilis required ≥21; and Z. rouxii could be sterilized at 10 MPa and 26. The greater
resistance of Z. rouxii compared to T. versatilis and S. cerevisiae is shown in Figure 19–3.
Encapsulated viruses such as cytomegalovirus and herpes simplex type 1 have been found to be
inactivated at 300 MPa and 25
◦ C for 10 minutes. The pressure appears to damage the viral capsule
and prevent the binding of viral particles to host cells. On the other hand, sindbis virus resisted 700
MPa.
8