Control by Antimicrobial Preservatives and Bacteriophages ◾ 493
reactions with some enzymes in vegetative cells and germinating spores, restriction of the bacterial
use of iron, and interference with membrane permeability, thereby limiting transport. In addition
to clostridial species, nitrite is inhibitory, to some extent, to Staphylococcus aureus, Escherichia,
Pseudomonas, and Enterobacter spp. at 200 ppm; Lactobacillus and Salmonella serovars seem to be
resistant to this concentration of NO 2 .
The antibacterial effect of NO 2 is enhanced at lower pH (pH 5.0–6.0), in the presence of
reducing agents (e.g., ascorbate, erythorbate, and cysteine), and with sorbate. The current regulatory limit in the United States is 156 ppm of NO 2 , but this varies widely in other countries.
This amount can also be reduced by supplementing NO 2 with other reducing agents as well as
sorbates. The NO 2 effect is also enhanced by reducing A W and at low Eh. In cured meat products,
NO 2 reacts with myoglobin to form a stable pink color of nitrosyl hemochrome during heating.
In bacon, nitrite can lead to the formation of carcinogenic compounds, such as nitrosoamines.
Because of this, there is a trend to reduce NO 2 or to use other preservatives to control Clo. botulinum in low-heat-processed meat products.
Sulfur Dioxide (SO 2 ) and Sulfites (SO 3 )
Sulfur dioxide, sodium sulfite (Na 2 SO 3 ), sodium bisulfide (NaHSO 3 ), and sodium metabisulfite
(Na 2 S 2 O 5 ) are used to control microorganisms (and insects) in soft fruits, fruit juices, lemon
juices, beverages, wines, sausages, pickles, and fresh shrimp.
Currently, these additives are not permitted in the United States in meat, as they destroy
vitamin B 1 . They are more effective against molds and yeasts than bacteria; among bacteria, the
aerobic gram-negative rods are the most susceptible. The antimicrobial action is produced by the
undissociated sulfurous acid that rapidly enters the cell and reacts with the thiol groups in structural proteins, enzymes, and cofactors, as well as with other cellular components. At low pH (≤4.5)
and low A W , the fungicidal effect is more pronounced. In bacteria, they are effective at high pH
(≥5.0) but are probably bacteriostatic at lower concentrations and bactericidal at higher concentrations. The concentrations used in foods vary greatly in different countries. In the United States,
200–300 ppm is generally permitted for antimicrobial uses.
Sulfur dioxide and sulfites are also used as antioxidants in fresh and dried fruits and vegetables
(salads) to prevent browning. However, people with respiratory problems can be mildly to severely
allergic to sulfites. The products need to be labeled to show the presence of sulfites.
H 2 O 2
Hydrogen peroxide is also produced during microbial fermentation and is used as a food preservative
(see Chapter 17). A solution of H 2 O 2 (0.05%–0.1%) is recommended as an antimicrobial agent in raw
milk to be used in cheese processing (to control growth of psychrotrophic gram-negatives that produce heat-stable enzymes), liquid egg to facilitate destruction of Salmonella by low-heat pasteurization,
packaging material used in aseptic packaging of foods, and food processing equipment. In raw milk
and liquid egg, catalase is used before pasteurization to hydrolyze H 2 O 2 to water and oxygen. H 2 O 2 is
a strong oxidizing agent, and the germicidal action is associated with this property (see Chapter 17).
Recently, H 2 O 2 has been used to produce modified plant fiber flour from straws for use in lowcalorie foods; for bleaching and color improvement of grains, chocolate, instant tea, fish, sausage
casings, and many others; and to reduce sulfite in wines. In the future, the use of H 2 O 2 in foods
is expected to increase.
reactions with some enzymes in vegetative cells and germinating spores, restriction of the bacterial
use of iron, and interference with membrane permeability, thereby limiting transport. In addition
to clostridial species, nitrite is inhibitory, to some extent, to Staphylococcus aureus, Escherichia,
Pseudomonas, and Enterobacter spp. at 200 ppm; Lactobacillus and Salmonella serovars seem to be
resistant to this concentration of NO 2 .
The antibacterial effect of NO 2 is enhanced at lower pH (pH 5.0–6.0), in the presence of
reducing agents (e.g., ascorbate, erythorbate, and cysteine), and with sorbate. The current regulatory limit in the United States is 156 ppm of NO 2 , but this varies widely in other countries.
This amount can also be reduced by supplementing NO 2 with other reducing agents as well as
sorbates. The NO 2 effect is also enhanced by reducing A W and at low Eh. In cured meat products,
NO 2 reacts with myoglobin to form a stable pink color of nitrosyl hemochrome during heating.
In bacon, nitrite can lead to the formation of carcinogenic compounds, such as nitrosoamines.
Because of this, there is a trend to reduce NO 2 or to use other preservatives to control Clo. botulinum in low-heat-processed meat products.
Sulfur Dioxide (SO 2 ) and Sulfites (SO 3 )
Sulfur dioxide, sodium sulfite (Na 2 SO 3 ), sodium bisulfide (NaHSO 3 ), and sodium metabisulfite
(Na 2 S 2 O 5 ) are used to control microorganisms (and insects) in soft fruits, fruit juices, lemon
juices, beverages, wines, sausages, pickles, and fresh shrimp.
Currently, these additives are not permitted in the United States in meat, as they destroy
vitamin B 1 . They are more effective against molds and yeasts than bacteria; among bacteria, the
aerobic gram-negative rods are the most susceptible. The antimicrobial action is produced by the
undissociated sulfurous acid that rapidly enters the cell and reacts with the thiol groups in structural proteins, enzymes, and cofactors, as well as with other cellular components. At low pH (≤4.5)
and low A W , the fungicidal effect is more pronounced. In bacteria, they are effective at high pH
(≥5.0) but are probably bacteriostatic at lower concentrations and bactericidal at higher concentrations. The concentrations used in foods vary greatly in different countries. In the United States,
200–300 ppm is generally permitted for antimicrobial uses.
Sulfur dioxide and sulfites are also used as antioxidants in fresh and dried fruits and vegetables
(salads) to prevent browning. However, people with respiratory problems can be mildly to severely
allergic to sulfites. The products need to be labeled to show the presence of sulfites.
H 2 O 2
Hydrogen peroxide is also produced during microbial fermentation and is used as a food preservative
(see Chapter 17). A solution of H 2 O 2 (0.05%–0.1%) is recommended as an antimicrobial agent in raw
milk to be used in cheese processing (to control growth of psychrotrophic gram-negatives that produce heat-stable enzymes), liquid egg to facilitate destruction of Salmonella by low-heat pasteurization,
packaging material used in aseptic packaging of foods, and food processing equipment. In raw milk
and liquid egg, catalase is used before pasteurization to hydrolyze H 2 O 2 to water and oxygen. H 2 O 2 is
a strong oxidizing agent, and the germicidal action is associated with this property (see Chapter 17).
Recently, H 2 O 2 has been used to produce modified plant fiber flour from straws for use in lowcalorie foods; for bleaching and color improvement of grains, chocolate, instant tea, fish, sausage
casings, and many others; and to reduce sulfite in wines. In the future, the use of H 2 O 2 in foods
is expected to increase.