Food Protection with Chemicals, and by Biocontrol 337
Among some of its desirable properties as a food preservative are the following:
• It is nontoxic.
• It is produced naturally by Lactococcus lactis strains.
• It is heat stable and has excellent storage stability.
• It is destroyed by digestive enzymes.
• It does not contribute to off-flavors or off-odors.
• It has a narrow spectrum of antimicrobial activity.
A large amount of research has been carried out with nisin as a heat adjunct in canned foods or as
an inhibitor of heat-shocked spores of Bacillus and Clostridium strains, and the MIC for preventing
outgrowth of germinating spores ranges widely from 3 to >5,000 IU/ml or <1 to >125 ppm (1 µg of
pure nisin is about 40 IU or RU—Reading unit).
88 Depending on the country and the food product,
typical usable levels are in the range of about 2.5–100 ppm, although some countries do not impose
concentration limits. Nisin has been combined with low heat to destroy L. monocytogenes in cold-pack
lobster meat. When using a brine at about pH 8.0 and nisin at 25 mg/kg of can contents at 60
◦ C for
5 minutes using two can sizes, a 3- to 5-log reduction of inoculated cells was achieved, whereas with
nisin alone the reduction was only 1–3 logs.
22
A conventional heat process for low-acid canned foods requires an F 0 treatment of 6–8 (see Chapter
17) to inactivate the endospores of both C. botulinum and spoilage organisms. By adding nisin, the heat
process can be reduced to an F o of 3 (to inactivate C. botulinum spores), resulting in increased product
quality of low-acid canned foods. Whereas the low-heat treatment will not destroy the endospores
of spoilage organisms, nisin prevents their germination by acting early in the endospore germination
cycle (Figure 13–1). In addition to its use in certain canned foods, nisin is most often employed in dairy
products—processed cheeses, condensed milk, pasteurized milk, and so on. Some countries permit its
use in processed tomato products and canned fruits and vegetables.
88 It is most stable in acidic foods.
Because of the effectiveness of nisin in preventing the outgrowth of germinating endospores of
C. botulinum and the search to find safe substances that might replace nitrites in processed meats,
this agent has been studied as a possible replacement for nitrite. Although some studies showed encouraging results employing C. sporogenes and other nonpathogenic organisms, a study employing
C. botulinum types A and B spores in pork slurries indicated the inability of nisin at concentrations
up to 550 ppm in combination with 60 ppm of nitrite to inhibit spore outgrowth.
154 Employed in
culture media without added nitrite, the quantity of nisin required for 50% inhibition of C. botulinum
type E spores was 1–2 ppm, 10–20 ppm for type B, and 20–40 ppm for type A.
172 The latter investigators found that higher levels were required for inhibition in cooked meat medium than in TPYG
medium and suggested that nisin was approximately equivalent to nitrite in preventing the outgrowth of
C. botulinum spores.
A system of classifying bacteriocins that places them into one of four classes has been presented.
The Klaenhammer system is based primarily on the genetics and biochemistry of these compounds.
Class I includes the lantibiotics such as nisin; class II are small heat-stable peptides such as lactacin
F; class III are large heat-labile proteins such as helveticin J; and class IV are proteins that form a
complex with other factors.
Unlike antibiotics, bacteriocins generally inhibit only closely related species and strains of Grampositive bacteria. They consist of small proteins, and most are plasmid mediated. It appears that some
species and strains of all genera of lactic acid bacteria possess the capacity to produce bacteriocins
or bacteriocin-like compounds. Although early attention was focused on the lactics associated with
dairy products, producing species and strains have been recovered from meats and other nondairy
Among some of its desirable properties as a food preservative are the following:
• It is nontoxic.
• It is produced naturally by Lactococcus lactis strains.
• It is heat stable and has excellent storage stability.
• It is destroyed by digestive enzymes.
• It does not contribute to off-flavors or off-odors.
• It has a narrow spectrum of antimicrobial activity.
A large amount of research has been carried out with nisin as a heat adjunct in canned foods or as
an inhibitor of heat-shocked spores of Bacillus and Clostridium strains, and the MIC for preventing
outgrowth of germinating spores ranges widely from 3 to >5,000 IU/ml or <1 to >125 ppm (1 µg of
pure nisin is about 40 IU or RU—Reading unit).
88 Depending on the country and the food product,
typical usable levels are in the range of about 2.5–100 ppm, although some countries do not impose
concentration limits. Nisin has been combined with low heat to destroy L. monocytogenes in cold-pack
lobster meat. When using a brine at about pH 8.0 and nisin at 25 mg/kg of can contents at 60
◦ C for
5 minutes using two can sizes, a 3- to 5-log reduction of inoculated cells was achieved, whereas with
nisin alone the reduction was only 1–3 logs.
22
A conventional heat process for low-acid canned foods requires an F 0 treatment of 6–8 (see Chapter
17) to inactivate the endospores of both C. botulinum and spoilage organisms. By adding nisin, the heat
process can be reduced to an F o of 3 (to inactivate C. botulinum spores), resulting in increased product
quality of low-acid canned foods. Whereas the low-heat treatment will not destroy the endospores
of spoilage organisms, nisin prevents their germination by acting early in the endospore germination
cycle (Figure 13–1). In addition to its use in certain canned foods, nisin is most often employed in dairy
products—processed cheeses, condensed milk, pasteurized milk, and so on. Some countries permit its
use in processed tomato products and canned fruits and vegetables.
88 It is most stable in acidic foods.
Because of the effectiveness of nisin in preventing the outgrowth of germinating endospores of
C. botulinum and the search to find safe substances that might replace nitrites in processed meats,
this agent has been studied as a possible replacement for nitrite. Although some studies showed encouraging results employing C. sporogenes and other nonpathogenic organisms, a study employing
C. botulinum types A and B spores in pork slurries indicated the inability of nisin at concentrations
up to 550 ppm in combination with 60 ppm of nitrite to inhibit spore outgrowth.
154 Employed in
culture media without added nitrite, the quantity of nisin required for 50% inhibition of C. botulinum
type E spores was 1–2 ppm, 10–20 ppm for type B, and 20–40 ppm for type A.
172 The latter investigators found that higher levels were required for inhibition in cooked meat medium than in TPYG
medium and suggested that nisin was approximately equivalent to nitrite in preventing the outgrowth of
C. botulinum spores.
A system of classifying bacteriocins that places them into one of four classes has been presented.
The Klaenhammer system is based primarily on the genetics and biochemistry of these compounds.
Class I includes the lantibiotics such as nisin; class II are small heat-stable peptides such as lactacin
F; class III are large heat-labile proteins such as helveticin J; and class IV are proteins that form a
complex with other factors.
Unlike antibiotics, bacteriocins generally inhibit only closely related species and strains of Grampositive bacteria. They consist of small proteins, and most are plasmid mediated. It appears that some
species and strains of all genera of lactic acid bacteria possess the capacity to produce bacteriocins
or bacteriocin-like compounds. Although early attention was focused on the lactics associated with
dairy products, producing species and strains have been recovered from meats and other nondairy