198 Modern Food Microbiology
the synthetic pie base contained fewer than log 10 2.00 bacteria per gram after final heating to 160
◦ F
(71.1
◦ C). After overnight storage, however, the count rose to log 10 4.15. The pie topping ingredients
to be mixed with the pie base had a rather low count: log 2.78/g. After being deposited on the pies,
the pie topping showed a total count of log 10 7.00/g. In a study of the microbiological quality of
french fries, Surkiewicz et al.
57 demonstrated the same pattern—that is, the successive buildup of
microorganisms as the fries underwent processing. Because these products are cooked late in their
processing, the incidence of organisms in the finished state does not properly reflect the actual state
of sanitation during processing.
The geometric mean APC of 1,187 sample units of refrigerated biscuit dough was found to be
34,000/g, whereas for fungi, coliforms, E. coli, and S. aureus, the mean counts were 46, 11, <3, and
<3/g, respectively.
58 In the same study, the geometric mean APC of 1,396 units of snack cake was
910/g, with <3/g of coliforms, E. coli, and S. aureus (see Table 9–1).
A bacteriological study of 580 frozen cream-type pies (lemon, coconut, chocolate, and banana)
showed them to be of excellent quality, with 98% having an APC of log 4.70 or less/g.
33 The overall
microbiological quality of other related products is presented in Table 9–1. A summary of mean
numbers of L. monocytogenes andSalmonella spp. in 11 ready-to-eat products in the United States for
the 10-year period 1990–1999 is presented in Table 9–2,
35 and the prevalence of Aeromonas spp. in
four ready-to-eat foods in Italy is presented in Table 9–3.
62
EGGS
The hen’s egg is an excellent example of a product that normally is well protected by its intrinsic
parameters. Externally, a fresh egg has three structures, each effective to some degree in retarding the
entry of microorganisms: the outer waxy shell membrane; the shell; and the inner shell membrane
(Figure 9–1). Internally, lysozyme is present in egg white. This enzyme is quite effective against
Gram-positive bacteria. Egg white also contains avidin, which forms a complex with biotin, thereby
making this vitamin unavailable to microorganisms. In addition, egg white has a high pH (about
9.3) and contains conalbumin, which forms a complex with iron, thus rendering it unavailable to
microorganisms. On the other hand, the nutrient content of the yolk material and its pH in fresh eggs
(about 6.8) make it an excellent source of growth for most microorganisms.
Freshly laid eggs are generally sterile. However, in a relatively short period of time after laying,
numerous microorganisms may be found on the outside and, under the proper conditions, may enter
eggs, grow, and cause spoilage. The speed at which microbes enter eggs is related to temperature of
storage, age of eggs, and level of contamination. The use of cryogenic gas (CO 2 ) to effect the rapid
cooling of eggs led to fewer bacteria in the interior compared to conventional cooling, even though the
differences were less significant after 30-day storage at 7
◦ C.
8 A study of the migration of artificially
contaminated S.Enteritidis from the albumen into the egg yolk using 860 eggs revealed that this
bacterium could be detected in yolk within a day, depending on storage temperature and contamination
level. Migration occurred in 1 day at 30
◦ C but not until 14 days at 7
◦ C.
2 Also, 1-day-old eggs were
more resistant than 4-week-old eggs, and the speed of migration was positively correlated with the
level of contamination. The deposing of S.Enteritidis in eggs by the hen before they are laid has
been demonstrated (see reference 22). Among the bacteria found were members of the following
genera: Pseudomonas, Acinetobacter, Proteus, Aeromonas, Alcaligenes, Escherichia, Micrococcus,
Salmonella, Serratia, Enterobacter, Flavobacterium, and Staphylococcus. Among the molds generally
found are members of the genera Mucor, Penicillium, Hormodendron, Cladosporium, and others;
“Torula” is the only yeast found with any degree of consistency. The most common form of bacterial
spoilage of eggs is a condition known as rotting. Green rots are caused by Pseudomonas spp., especially
the synthetic pie base contained fewer than log 10 2.00 bacteria per gram after final heating to 160
◦ F
(71.1
◦ C). After overnight storage, however, the count rose to log 10 4.15. The pie topping ingredients
to be mixed with the pie base had a rather low count: log 2.78/g. After being deposited on the pies,
the pie topping showed a total count of log 10 7.00/g. In a study of the microbiological quality of
french fries, Surkiewicz et al.
57 demonstrated the same pattern—that is, the successive buildup of
microorganisms as the fries underwent processing. Because these products are cooked late in their
processing, the incidence of organisms in the finished state does not properly reflect the actual state
of sanitation during processing.
The geometric mean APC of 1,187 sample units of refrigerated biscuit dough was found to be
34,000/g, whereas for fungi, coliforms, E. coli, and S. aureus, the mean counts were 46, 11, <3, and
<3/g, respectively.
58 In the same study, the geometric mean APC of 1,396 units of snack cake was
910/g, with <3/g of coliforms, E. coli, and S. aureus (see Table 9–1).
A bacteriological study of 580 frozen cream-type pies (lemon, coconut, chocolate, and banana)
showed them to be of excellent quality, with 98% having an APC of log 4.70 or less/g.
33 The overall
microbiological quality of other related products is presented in Table 9–1. A summary of mean
numbers of L. monocytogenes andSalmonella spp. in 11 ready-to-eat products in the United States for
the 10-year period 1990–1999 is presented in Table 9–2,
35 and the prevalence of Aeromonas spp. in
four ready-to-eat foods in Italy is presented in Table 9–3.
62
EGGS
The hen’s egg is an excellent example of a product that normally is well protected by its intrinsic
parameters. Externally, a fresh egg has three structures, each effective to some degree in retarding the
entry of microorganisms: the outer waxy shell membrane; the shell; and the inner shell membrane
(Figure 9–1). Internally, lysozyme is present in egg white. This enzyme is quite effective against
Gram-positive bacteria. Egg white also contains avidin, which forms a complex with biotin, thereby
making this vitamin unavailable to microorganisms. In addition, egg white has a high pH (about
9.3) and contains conalbumin, which forms a complex with iron, thus rendering it unavailable to
microorganisms. On the other hand, the nutrient content of the yolk material and its pH in fresh eggs
(about 6.8) make it an excellent source of growth for most microorganisms.
Freshly laid eggs are generally sterile. However, in a relatively short period of time after laying,
numerous microorganisms may be found on the outside and, under the proper conditions, may enter
eggs, grow, and cause spoilage. The speed at which microbes enter eggs is related to temperature of
storage, age of eggs, and level of contamination. The use of cryogenic gas (CO 2 ) to effect the rapid
cooling of eggs led to fewer bacteria in the interior compared to conventional cooling, even though the
differences were less significant after 30-day storage at 7
◦ C.
8 A study of the migration of artificially
contaminated S.Enteritidis from the albumen into the egg yolk using 860 eggs revealed that this
bacterium could be detected in yolk within a day, depending on storage temperature and contamination
level. Migration occurred in 1 day at 30
◦ C but not until 14 days at 7
◦ C.
2 Also, 1-day-old eggs were
more resistant than 4-week-old eggs, and the speed of migration was positively correlated with the
level of contamination. The deposing of S.Enteritidis in eggs by the hen before they are laid has
been demonstrated (see reference 22). Among the bacteria found were members of the following
genera: Pseudomonas, Acinetobacter, Proteus, Aeromonas, Alcaligenes, Escherichia, Micrococcus,
Salmonella, Serratia, Enterobacter, Flavobacterium, and Staphylococcus. Among the molds generally
found are members of the genera Mucor, Penicillium, Hormodendron, Cladosporium, and others;
“Torula” is the only yeast found with any degree of consistency. The most common form of bacterial
spoilage of eggs is a condition known as rotting. Green rots are caused by Pseudomonas spp., especially