278 ◾ Fundamental Food Microbiology
carrying the primal cuts for vacuum packaging (in a plant having the specific problem). Three
of the 25 samples were positive for Clo. laramie, and all three were from the conveyor system at
the vacuum-packaging area. The conveyor system used by this plant consisted of small links. In
general, the microbiological quality of the meat was very good (~10 3 /g aerobic plate counts, APCs).
It was suspected that the sanitation specifically designed to keep the microbial load low was good
but was unable to kill the spores, especially in the inaccessible joints (dead spots) and similar places
in the links of the conveyor system. Thus, the fabricated meats were constantly inoculated with
the spores (and cells), which, in the absence of competition, because of low associated bacteria,
germinated or grew (or both) to cause large-scale spoilage (along with psychrotrophic Leuconostoc
spp.). Subsequent studies with spoiled meat samples from several beef processors having similar
problems in the United States have revealed that this incidence is not isolated, and more than one
strain of Clo. laramie is involved in spoilage. 5–8
A similar spoilage of vacuum-packaged refrigerated beef in Europe was also reported to be
caused by a similar Clostridium sp. and named Clo. estertheticum. This species also could not be
enumerated by agar-plating methods and was first detected microscopically. 7 Other clostridial
species that are involved in the spoilage of vacuum-packaged meat include Clo. algidicarnis, Clo.
algidixylanolyticum, Clo. frigidicarnis, and Clo. gasigenes. 9 In recent years, spoilage of vacuumpackaged refrigerated raw beef by Clostridium spp. has been reported from Canada, Brazil, and
New Zealand.
Spoilage of Roasted Beef by Clostridium Species
Clostridium spp. have been isolated from at least two separate incidents of large-scale spoilage
of vacuum-packaged refrigerated roasted beef produced commercially. The meats (10–12 lbs
[4.5– 5.5 kg] each) were roasted ≤160°F (71°C) (internal temperature) and then vacuum-packaged
and refrigerated. 6,8 When the samples were received in the laboratory, they had large quantities of
gas and purge, but because of the spices used in the meat, only a strong spicy smell was evident.
Phase-contrast microscopy of the purge revealed large numbers of motile Clostridium cells, some
with typical terminal spores. Colonies of this bacterium were not obtained by isolation in specific
agar media, but large numbers of leuconostoc colonies (~10 8 /mL of purge) were obtained. The
spore-containing purge was heated and cultured to purify the Clostridium spp. Inoculation of
the pure culture to rare roasted beef, followed by vacuum packaging and refrigeration, showed
the formation of H 2 S gas, a change of meat color from light brown to pink, and accumulation of
pink to red purge within 2–3 weeks. Examination of the purge under a phase-contrast microscope
revealed the presence of Clostridium cells and spores. Some of these isolates seem to differ in some
biochemical and physiological patterns when compared with Clo. laramie isolated from the spoiled
raw beef (see the section on spoilage of unprocessed (fresh) beef by Clostridium spp.). 5,7
Spoilage of Pork Chops by Clostridium algidicarnis
This new species is associated with spoilage of cooked, vacuum-packaged pork meat products during storage at 4°C. 10 It produces an offensive spoilage odor.
Spoilage of Tofu by Clostridium Species
A vacuum-packaged soybean milk curd product (tofu) during refrigerated storage revealed gas
and liquid accumulation in the bag and off-flavor (Figure 21.1b). 8 Microscopic examination of the
carrying the primal cuts for vacuum packaging (in a plant having the specific problem). Three
of the 25 samples were positive for Clo. laramie, and all three were from the conveyor system at
the vacuum-packaging area. The conveyor system used by this plant consisted of small links. In
general, the microbiological quality of the meat was very good (~10 3 /g aerobic plate counts, APCs).
It was suspected that the sanitation specifically designed to keep the microbial load low was good
but was unable to kill the spores, especially in the inaccessible joints (dead spots) and similar places
in the links of the conveyor system. Thus, the fabricated meats were constantly inoculated with
the spores (and cells), which, in the absence of competition, because of low associated bacteria,
germinated or grew (or both) to cause large-scale spoilage (along with psychrotrophic Leuconostoc
spp.). Subsequent studies with spoiled meat samples from several beef processors having similar
problems in the United States have revealed that this incidence is not isolated, and more than one
strain of Clo. laramie is involved in spoilage. 5–8
A similar spoilage of vacuum-packaged refrigerated beef in Europe was also reported to be
caused by a similar Clostridium sp. and named Clo. estertheticum. This species also could not be
enumerated by agar-plating methods and was first detected microscopically. 7 Other clostridial
species that are involved in the spoilage of vacuum-packaged meat include Clo. algidicarnis, Clo.
algidixylanolyticum, Clo. frigidicarnis, and Clo. gasigenes. 9 In recent years, spoilage of vacuumpackaged refrigerated raw beef by Clostridium spp. has been reported from Canada, Brazil, and
New Zealand.
Spoilage of Roasted Beef by Clostridium Species
Clostridium spp. have been isolated from at least two separate incidents of large-scale spoilage
of vacuum-packaged refrigerated roasted beef produced commercially. The meats (10–12 lbs
[4.5– 5.5 kg] each) were roasted ≤160°F (71°C) (internal temperature) and then vacuum-packaged
and refrigerated. 6,8 When the samples were received in the laboratory, they had large quantities of
gas and purge, but because of the spices used in the meat, only a strong spicy smell was evident.
Phase-contrast microscopy of the purge revealed large numbers of motile Clostridium cells, some
with typical terminal spores. Colonies of this bacterium were not obtained by isolation in specific
agar media, but large numbers of leuconostoc colonies (~10 8 /mL of purge) were obtained. The
spore-containing purge was heated and cultured to purify the Clostridium spp. Inoculation of
the pure culture to rare roasted beef, followed by vacuum packaging and refrigeration, showed
the formation of H 2 S gas, a change of meat color from light brown to pink, and accumulation of
pink to red purge within 2–3 weeks. Examination of the purge under a phase-contrast microscope
revealed the presence of Clostridium cells and spores. Some of these isolates seem to differ in some
biochemical and physiological patterns when compared with Clo. laramie isolated from the spoiled
raw beef (see the section on spoilage of unprocessed (fresh) beef by Clostridium spp.). 5,7
Spoilage of Pork Chops by Clostridium algidicarnis
This new species is associated with spoilage of cooked, vacuum-packaged pork meat products during storage at 4°C. 10 It produces an offensive spoilage odor.
Spoilage of Tofu by Clostridium Species
A vacuum-packaged soybean milk curd product (tofu) during refrigerated storage revealed gas
and liquid accumulation in the bag and off-flavor (Figure 21.1b). 8 Microscopic examination of the