336 Modern Food Microbiology
controls.
101 When added to the surfaces of beef steaks inoculated with E. coli or S.Typhimurium and
stored at 5
◦ C, Lactobacillus delbrueckii subsp. lactis effected a significant reduction of psychrotrophs
and coliforms, and a slight reduction in E. coli.
173 Significant reductions of both pathogens as well as
psychrotrophs occurred when the lactic culture was applied to the surfaces of freshly slaughtered beef
and pork carcass samples. The effectiveness of Leuconostoc carnosum against L. monocytogenes on
cooked, sliced, and modified atmosphere packaged cooked meat (saveloy) has been demonstrated.
92
The most effective method used was spraying the lactic organism on meat surfaces, which kept
L. monocytogenes to 10 cfu/g for 4 weeks at 10
◦ C compared to controls where the pathogen increased
to ca. 10
7 cfu/g.
92
Regarding further reports on the protective effects of lactics in meat products, a study in Norway
using cooked, sliced, modified-atmosphere-packaged ham and sausage meats that were inoculated
with 10
4 –10
5 /g of a five-strain mixture of Lactobacillus sakei, it prevented the growth of added
L. monocytogenes and E. coli 0157:H7 when held at 8
◦ C for 21 days although a serotype 0:3 strain of
Yersinia enterocolitica was unaffected.
20 All meats were acceptable at the end of the storage period.
When 1,180 psychrotrophic isolates from salad vegetables were tested by agar plate assay against
S. aureus, E. coli 0157:H7, L. monocytogenes, and S. Montevideo, 37 (3.2%) of the isolates displayed varying degrees of inhibition against at least one of the four pathogens.
171 Thirty-four of the
37 inhibitory cultures were Gram negative. A hydrogen-peroxide-producing strain of Lactobacillus
delbrueckii subsp. lactis was added to several fresh-cut vegetables along with E. coli 0157:H7 and
L. monocytogenes and incubated at 7
◦ C for up to 6 days. There was no reduction of pathogens, apparently because the catalase in the cut vegetables destroyed the hydrogen peroxide by the lactic culture.
78
When a foodborne strain of Staphylococcus equorum was tested against 95 Listeria strains (all species
included), all were inhibited.
28 All but one of 131 other species and strains of Gram-positive bacteria
were inhibited while 37 strains of 6 Gram-negative species were not.
28
Protective cultures refer to the microorganisms that can be found in or added to a food product
to effect preservation/protection, and this concept was advanced by Holzapfel et al.
83 The organisms
noted above under lactic antagonism fit the definition of protective cultures. Among the properties
that the latter should possess are: (1) they should present no health risks, (2) provide beneficial effects
on the product, (3) have no negative impact on sensory properties, and (4) serve as “indicators” under
abuse conditions.
83 Again, the lactic acid bacteria constitute the largest and most important group that
falls under this category.
Nisin and Other Bacteriocins
Nisin
Nisin is produced by some strains of Lactococcus lactis, and it is a lantibiotic (contains the rare
amino acids, meso-lanthionine and 3-methyl-lanthione). It is the prototype of foodborne bacteriocins,
and its polypeptide structure is shown in Figure 13–6. The C-terminal amino acids are similar; the
N-terminals are not. The first use of nisin as food was shown by Hurst
88 to prevent the spoilage of
Swiss cheese by Clostridium butyricum. It is clearly the most widely used of these compounds for
food preservation, with around 50 countries permitting its use in foods to varying degrees.
40 It was
approved in 1988 for use in food in the United States, its use being limited to pasteurized processed
cheese spreads. It is a hydrophobic compound, and it can be degraded by metabisulfite, titanium oxide,
and certain proteolytic enzymes. The compound is effective against Gram-positive bacteria, primarily
spore formers, and is ineffective against fungi and Gram-negative bacteria. Enterococcus faecalis is
one of the most resistant Gram positives.
controls.
101 When added to the surfaces of beef steaks inoculated with E. coli or S.Typhimurium and
stored at 5
◦ C, Lactobacillus delbrueckii subsp. lactis effected a significant reduction of psychrotrophs
and coliforms, and a slight reduction in E. coli.
173 Significant reductions of both pathogens as well as
psychrotrophs occurred when the lactic culture was applied to the surfaces of freshly slaughtered beef
and pork carcass samples. The effectiveness of Leuconostoc carnosum against L. monocytogenes on
cooked, sliced, and modified atmosphere packaged cooked meat (saveloy) has been demonstrated.
92
The most effective method used was spraying the lactic organism on meat surfaces, which kept
L. monocytogenes to 10 cfu/g for 4 weeks at 10
◦ C compared to controls where the pathogen increased
to ca. 10
7 cfu/g.
92
Regarding further reports on the protective effects of lactics in meat products, a study in Norway
using cooked, sliced, modified-atmosphere-packaged ham and sausage meats that were inoculated
with 10
4 –10
5 /g of a five-strain mixture of Lactobacillus sakei, it prevented the growth of added
L. monocytogenes and E. coli 0157:H7 when held at 8
◦ C for 21 days although a serotype 0:3 strain of
Yersinia enterocolitica was unaffected.
20 All meats were acceptable at the end of the storage period.
When 1,180 psychrotrophic isolates from salad vegetables were tested by agar plate assay against
S. aureus, E. coli 0157:H7, L. monocytogenes, and S. Montevideo, 37 (3.2%) of the isolates displayed varying degrees of inhibition against at least one of the four pathogens.
171 Thirty-four of the
37 inhibitory cultures were Gram negative. A hydrogen-peroxide-producing strain of Lactobacillus
delbrueckii subsp. lactis was added to several fresh-cut vegetables along with E. coli 0157:H7 and
L. monocytogenes and incubated at 7
◦ C for up to 6 days. There was no reduction of pathogens, apparently because the catalase in the cut vegetables destroyed the hydrogen peroxide by the lactic culture.
78
When a foodborne strain of Staphylococcus equorum was tested against 95 Listeria strains (all species
included), all were inhibited.
28 All but one of 131 other species and strains of Gram-positive bacteria
were inhibited while 37 strains of 6 Gram-negative species were not.
28
Protective cultures refer to the microorganisms that can be found in or added to a food product
to effect preservation/protection, and this concept was advanced by Holzapfel et al.
83 The organisms
noted above under lactic antagonism fit the definition of protective cultures. Among the properties
that the latter should possess are: (1) they should present no health risks, (2) provide beneficial effects
on the product, (3) have no negative impact on sensory properties, and (4) serve as “indicators” under
abuse conditions.
83 Again, the lactic acid bacteria constitute the largest and most important group that
falls under this category.
Nisin and Other Bacteriocins
Nisin
Nisin is produced by some strains of Lactococcus lactis, and it is a lantibiotic (contains the rare
amino acids, meso-lanthionine and 3-methyl-lanthione). It is the prototype of foodborne bacteriocins,
and its polypeptide structure is shown in Figure 13–6. The C-terminal amino acids are similar; the
N-terminals are not. The first use of nisin as food was shown by Hurst
88 to prevent the spoilage of
Swiss cheese by Clostridium butyricum. It is clearly the most widely used of these compounds for
food preservation, with around 50 countries permitting its use in foods to varying degrees.
40 It was
approved in 1988 for use in food in the United States, its use being limited to pasteurized processed
cheese spreads. It is a hydrophobic compound, and it can be degraded by metabisulfite, titanium oxide,
and certain proteolytic enzymes. The compound is effective against Gram-positive bacteria, primarily
spore formers, and is ineffective against fungi and Gram-negative bacteria. Enterococcus faecalis is
one of the most resistant Gram positives.