356 Modern Food Microbiology
the permeability of cell membranes, and Enfors and Molin
22 found support for the latter hypothesis in
their studies on the germination of Clostridium sporogenes and C. perfringens endospores. At 1 atm
CO 2 , spore germination of these two species was stimulated, whereas B. cereus spore germination
was inhibited. As was shown by others, CO 2 is more stimulatory at low pH than at high pH. With
55 atm CO 2 , only 4% germination of C. sporogenes spores occurred, whereas with C. perfringens,
50 atm reduced germination to 4%.
22 These authors suggested that CO 2 inhibition was due to its
accumulation in the membrane lipid bilayer such that increased fluidity results. An adverse effect on
cell permeability has been suggested by others. If CO 2 is dissolved in the form of carbonic acid, HCO
−
3
would be present as a dissociation product, and thus can cause changes in cell permeability.
17 When
dissolved in water, CO 2 products are as follows:
CO 2 + H 2 O −
− H 2 CO 3 −
− H
+ + HCO
−
3
−
− 2H + CO
2−
3
The antimicrobial spectrum of CO 2 and diacetyl is quite similar, and while this per se does not mean
they possess identical modes of action, the striking similarities seem worthy of note. Diacetyl is an
arginine antagonist and its mode of action along with some other α-dicarbonyl compounds has been
discussed.
51 The greater sensitivity of Gram-negative bacteria to α-dicarbonyl inhibitors appears to be
due to their capacity to inactivate amino acid-binding proteins of the cell’s periplasm, especially the
arginine-binding proteins. Thus, it is not inconceivable that the site of action of CO 2 is the periplasm,
where it interferes with the normal functioning of amino acid-binding proteins.
Food Products
The successful use of vacuum packaging, MAP, and CAS to extend the self-life of a wide variety of
food products is well documented, and some of the specific antimicrobial aspects are outlined below.
Fresh and Processed Meats
Among the first to demonstrate the effectiveness of high levels of CO 2 in preserving cut-up meats
was J. Brooks in England, who in 1933 studied the effect of CO 2 on lean meat; E. Callow in England,
who studied pork and bacon; R.B. Haines, also in England, who was among the first to show the effect
of CO 2 on spoilage organisms; and W.A. Empey in Australia, who in 1933 applied CO 2 to beef.
73
In general, the self-life of red meats can be extended for up to 2 months if packaged in 75% O 2 +
25% CO 2 and stored at −1
◦ C. The high level of oxygen ensures that the red-meat color is maintained.
It has been shown that at least 15% CO 2 is necessary to retard microbial growth on beef steaks, and that
the mixture of 15% CO 2 + 75% O 2 + 10% N 2 was more effective than vacuum both for red-meat color
and microbial quality.
4 The importance of the temperature of storage of MAP meats was shown early
by Jaye et al.
52 who found striking differences in quality when ground beef was stored at 30
◦ C versus
38
◦ . They compared the use of the more gas-impermeable Saran to the gas-permeable cellophane
packs. Earlier, Halleck et al.
38 showed the dramatic inhibitory effect of vacuum packaging and storage
at 1.1–3.3
◦ C. The importance of temperature of storage was demonstrated in another study using the
packaging system known as the Captech process, which combines hygienic processing, storage at
−1.5
◦ C, high CO 2 , low O 2 , and gas-impermeable packaging.
36 The process was applied to pork loins,
with the temperature of holding for simulated retail display being raised to 8
◦ C. Lactic acid bacteria
grew without perceptible decrease in lag phase, and reached 10
7 /cm
2 within 9 weeks. The behavior of
the biota of smoked pork loins and frankfurter sausage stored under vacuum and CO 2 is presented in
the permeability of cell membranes, and Enfors and Molin
22 found support for the latter hypothesis in
their studies on the germination of Clostridium sporogenes and C. perfringens endospores. At 1 atm
CO 2 , spore germination of these two species was stimulated, whereas B. cereus spore germination
was inhibited. As was shown by others, CO 2 is more stimulatory at low pH than at high pH. With
55 atm CO 2 , only 4% germination of C. sporogenes spores occurred, whereas with C. perfringens,
50 atm reduced germination to 4%.
22 These authors suggested that CO 2 inhibition was due to its
accumulation in the membrane lipid bilayer such that increased fluidity results. An adverse effect on
cell permeability has been suggested by others. If CO 2 is dissolved in the form of carbonic acid, HCO
−
3
would be present as a dissociation product, and thus can cause changes in cell permeability.
17 When
dissolved in water, CO 2 products are as follows:
CO 2 + H 2 O −
− H 2 CO 3 −
− H
+ + HCO
−
3
−
− 2H + CO
2−
3
The antimicrobial spectrum of CO 2 and diacetyl is quite similar, and while this per se does not mean
they possess identical modes of action, the striking similarities seem worthy of note. Diacetyl is an
arginine antagonist and its mode of action along with some other α-dicarbonyl compounds has been
discussed.
51 The greater sensitivity of Gram-negative bacteria to α-dicarbonyl inhibitors appears to be
due to their capacity to inactivate amino acid-binding proteins of the cell’s periplasm, especially the
arginine-binding proteins. Thus, it is not inconceivable that the site of action of CO 2 is the periplasm,
where it interferes with the normal functioning of amino acid-binding proteins.
Food Products
The successful use of vacuum packaging, MAP, and CAS to extend the self-life of a wide variety of
food products is well documented, and some of the specific antimicrobial aspects are outlined below.
Fresh and Processed Meats
Among the first to demonstrate the effectiveness of high levels of CO 2 in preserving cut-up meats
was J. Brooks in England, who in 1933 studied the effect of CO 2 on lean meat; E. Callow in England,
who studied pork and bacon; R.B. Haines, also in England, who was among the first to show the effect
of CO 2 on spoilage organisms; and W.A. Empey in Australia, who in 1933 applied CO 2 to beef.
73
In general, the self-life of red meats can be extended for up to 2 months if packaged in 75% O 2 +
25% CO 2 and stored at −1
◦ C. The high level of oxygen ensures that the red-meat color is maintained.
It has been shown that at least 15% CO 2 is necessary to retard microbial growth on beef steaks, and that
the mixture of 15% CO 2 + 75% O 2 + 10% N 2 was more effective than vacuum both for red-meat color
and microbial quality.
4 The importance of the temperature of storage of MAP meats was shown early
by Jaye et al.
52 who found striking differences in quality when ground beef was stored at 30
◦ C versus
38
◦ . They compared the use of the more gas-impermeable Saran to the gas-permeable cellophane
packs. Earlier, Halleck et al.
38 showed the dramatic inhibitory effect of vacuum packaging and storage
at 1.1–3.3
◦ C. The importance of temperature of storage was demonstrated in another study using the
packaging system known as the Captech process, which combines hygienic processing, storage at
−1.5
◦ C, high CO 2 , low O 2 , and gas-impermeable packaging.
36 The process was applied to pork loins,
with the temperature of holding for simulated retail display being raised to 8
◦ C. Lactic acid bacteria
grew without perceptible decrease in lag phase, and reached 10
7 /cm
2 within 9 weeks. The behavior of
the biota of smoked pork loins and frankfurter sausage stored under vacuum and CO 2 is presented in