Food Protection with Modified Atmospheres
361
salmon-filled tortelli at day 30 (pH was 6.1, a w 0.95) and in the meat and ricotta–spinach tortelli at
day 50 but not in the artichoke-filled tortelli at day 50.
18
In an assessment of C. botulinum toxin production in cooked, uncured, turkey meat inoculated with
nonproteolytic type B, packaged in O 2 -impermeable bags stored under MAP, toxin was produced in
7 days at 15
◦ C, in 14 days at 10
◦ C, and in 28 days at 4
◦ C.
60 At the latter temperature, toxin appeared
in 14 days under 100% N 2 preceded or coincided with sensory spoilage.
Using cooked turkey breast that was inoculated with a nonproteolytic type B strain of C. botulinum,
samples were stored in O 2 -impermeable bags with either 100% N 2 or 70% N 2 + 30% CO 2 and
observed for toxin production. The turkey meat was positive for toxin at all temperatures and MAP
combinations used after sufficient incubation times. At 15
◦ C, toxin appeared after 7 days; after 4 days
at 10
◦ C; and after 14 days at 4
◦ C (in 100% N 2 and 28 days in CO 2 + N 2 combination).
60
Listeria monocytogenes
The fact that this bacterium can grow in the refrigerator temperature range raises concerns about its
presence and potential for growth in MAP foods. In a study using ground fresh top beef rounds with
a pH of 5.47 that were vacuum packaged and held at 4
◦ C for up to 56 days, one strain increased in
numbers by 2.3 logs (from 4.25 to 6.53) after 35 days, another increased by 1.8 logs after 35 days, and
a third was unchanged after 56 days.
3 With high-pH (6.14) beef, three strains of L. monocytogenes
increased significantly in 28 days, but strain Scott A did not.
In a study of the growth and survival of L. monocytogenes in vacuum-packaged ground beef (initial
pH 5.4) inoculated with Lactobacillus alimentarius (the FloraCarn L-2 strain, which is a homofermentative psychrotroph that can grow at 2
◦ C), L. monocytogenes numbers were reduced by the antilisterial
effects of the lactobacillus due apparently to its production of lactic acid, and this is illustrated in
Figure 14–3.
54
Regarding the behavior of this organism on vacuum-packaged beef, it has been shown that critical
factors are storage temperature, pH, and type of tissue, and whether lean or fat.
35 The organism grew
more extensively on fat than lean beef, and the background biota had no effect on its growth. At 5.3
◦ C,
it grew from about 10
3 to about 10
7 cfu/cm
2 in 16 days on fat, and in 20 days to 10
6 cfu/cm
2 on lean
tissue.
35 The organism grew faster on sirloins with pH 6.0–6.1 than those with pH 5.5–5.7. After 76
days at 0
◦ C, the organism reached 10
2 /cm
2 on fat and 10
4 cfu/cm
2 on lean.
32 In a prevalence study of
Listeria spp. on vacuum-packaged processed meats in the retail trade in Australia, listeriae were found
in 93 of 175 samples and L. monocytogenes was found on 78 of 93 samples.
34 It was found mainly
on corned beef and ham, and on two corned beef samples the numbers were >10
4 cfu/g. Strain Scott
A, when inoculated onto turkey roll slices at a level of about 10
3 /g and packaged in high-barrier bags
under 70% CO 2 + 30% N 2 , did not grow after 30 days at either 4
◦ C or 10
◦ C.
25 A 50:50 mixture of
CO 2 :N 2 was less inhibitory.
In a study of the growth of L. monocytogenes and Yersinia enterocolitica on cooked MAP poultry,
the product was stored in a CO 2 :N 2 mixture of 44:56 and stored at 3.5
◦ C, 6.5
◦ C, or 10
◦ C for up to 5
weeks.
2 Both organisms grew under all test conditions, and the naturally occurring microbiota did not
influence the growth of either. In a study of the effect of MAP and nisin on this organism in cooked
pork tenderloins, 100% CO 2 or 80% CO 2 + 20% air with 10
3 or 10
4 IU of nisin decreased the growth
not only of L. monocytogenes but also that of Pseudomonas fragi.
23
In a study of the changes in populations of L. monocytogenes on seven fresh-cut vegetables inoculated
with a five-strain cocktail at about 10
3 /g and stored in bags with an OTR of 2,100 cm
3 , the organism
remained constant on all vegetables that were stored at 4
◦ C for 9 days, but numbers declined on carrots
and increased on butternut squash.
24 At 10
◦ C, growth occurred on all except chopped carrots. The
antilisterial properties of carrots is well established (see Chapter 6). When prepeeled potatoes were
361
salmon-filled tortelli at day 30 (pH was 6.1, a w 0.95) and in the meat and ricotta–spinach tortelli at
day 50 but not in the artichoke-filled tortelli at day 50.
18
In an assessment of C. botulinum toxin production in cooked, uncured, turkey meat inoculated with
nonproteolytic type B, packaged in O 2 -impermeable bags stored under MAP, toxin was produced in
7 days at 15
◦ C, in 14 days at 10
◦ C, and in 28 days at 4
◦ C.
60 At the latter temperature, toxin appeared
in 14 days under 100% N 2 preceded or coincided with sensory spoilage.
Using cooked turkey breast that was inoculated with a nonproteolytic type B strain of C. botulinum,
samples were stored in O 2 -impermeable bags with either 100% N 2 or 70% N 2 + 30% CO 2 and
observed for toxin production. The turkey meat was positive for toxin at all temperatures and MAP
combinations used after sufficient incubation times. At 15
◦ C, toxin appeared after 7 days; after 4 days
at 10
◦ C; and after 14 days at 4
◦ C (in 100% N 2 and 28 days in CO 2 + N 2 combination).
60
Listeria monocytogenes
The fact that this bacterium can grow in the refrigerator temperature range raises concerns about its
presence and potential for growth in MAP foods. In a study using ground fresh top beef rounds with
a pH of 5.47 that were vacuum packaged and held at 4
◦ C for up to 56 days, one strain increased in
numbers by 2.3 logs (from 4.25 to 6.53) after 35 days, another increased by 1.8 logs after 35 days, and
a third was unchanged after 56 days.
3 With high-pH (6.14) beef, three strains of L. monocytogenes
increased significantly in 28 days, but strain Scott A did not.
In a study of the growth and survival of L. monocytogenes in vacuum-packaged ground beef (initial
pH 5.4) inoculated with Lactobacillus alimentarius (the FloraCarn L-2 strain, which is a homofermentative psychrotroph that can grow at 2
◦ C), L. monocytogenes numbers were reduced by the antilisterial
effects of the lactobacillus due apparently to its production of lactic acid, and this is illustrated in
Figure 14–3.
54
Regarding the behavior of this organism on vacuum-packaged beef, it has been shown that critical
factors are storage temperature, pH, and type of tissue, and whether lean or fat.
35 The organism grew
more extensively on fat than lean beef, and the background biota had no effect on its growth. At 5.3
◦ C,
it grew from about 10
3 to about 10
7 cfu/cm
2 in 16 days on fat, and in 20 days to 10
6 cfu/cm
2 on lean
tissue.
35 The organism grew faster on sirloins with pH 6.0–6.1 than those with pH 5.5–5.7. After 76
days at 0
◦ C, the organism reached 10
2 /cm
2 on fat and 10
4 cfu/cm
2 on lean.
32 In a prevalence study of
Listeria spp. on vacuum-packaged processed meats in the retail trade in Australia, listeriae were found
in 93 of 175 samples and L. monocytogenes was found on 78 of 93 samples.
34 It was found mainly
on corned beef and ham, and on two corned beef samples the numbers were >10
4 cfu/g. Strain Scott
A, when inoculated onto turkey roll slices at a level of about 10
3 /g and packaged in high-barrier bags
under 70% CO 2 + 30% N 2 , did not grow after 30 days at either 4
◦ C or 10
◦ C.
25 A 50:50 mixture of
CO 2 :N 2 was less inhibitory.
In a study of the growth of L. monocytogenes and Yersinia enterocolitica on cooked MAP poultry,
the product was stored in a CO 2 :N 2 mixture of 44:56 and stored at 3.5
◦ C, 6.5
◦ C, or 10
◦ C for up to 5
weeks.
2 Both organisms grew under all test conditions, and the naturally occurring microbiota did not
influence the growth of either. In a study of the effect of MAP and nisin on this organism in cooked
pork tenderloins, 100% CO 2 or 80% CO 2 + 20% air with 10
3 or 10
4 IU of nisin decreased the growth
not only of L. monocytogenes but also that of Pseudomonas fragi.
23
In a study of the changes in populations of L. monocytogenes on seven fresh-cut vegetables inoculated
with a five-strain cocktail at about 10
3 /g and stored in bags with an OTR of 2,100 cm
3 , the organism
remained constant on all vegetables that were stored at 4
◦ C for 9 days, but numbers declined on carrots
and increased on butternut squash.
24 At 10
◦ C, growth occurred on all except chopped carrots. The
antilisterial properties of carrots is well established (see Chapter 6). When prepeeled potatoes were