204 Modern Food Microbiology
still warm. Homemade breads may undergo a type of spoilage known as ropiness, which is caused
by the growth and amylase production of certain strains of Bacillus subtilis (B. mesentericus). The
ropiness may be seen as stringiness by carefully breaking a batch of dough into two parts. The source of
the organisms is flour, and their growth is favored by holding the dough for sufficient periods of time at
suitable temperatures. In a recent study, part-baked soda bread (pH 7–9) stored at room temperature
developed ropiness after 2 days, and three species were isolated from the ropy product: B. subtilis, B.
pumilus, and B. licheniformis.
34
Cakes of all types rarely undergo bacterial spoilage due to their unusually high concentrations of
sugars, which restrict the availability of water. The most common form of spoilage displayed by these
products is moldiness. Common sources of spoilage molds are any and all cake ingredients, especially
sugar, nuts, and spices. Although the baking process is generally sufficient to destroy these organisms,
many are added in icings, meringues, toppings, and so forth. Also, molds may enter baked cakes from
handling and from the air. Growth of molds on the surface of cakes is favored by conditions of high
humidity. On some fruitcakes, growth often originates underneath nuts and fruits if they are placed on
the surface of such products after baking. Continued growth of molds on breads and cakes results in
a hardening of the products.
FROZEN MEAT PIES
The microbiological quality of frozen meat pies has steadily improved since these products were first
marketed. Any and all of the ingredients added may increase the total number of organisms, and the
total count of the finished product may be taken to reflect the overall quality of ingredients, handling,
and storage. Many investigators have suggested that these products should be produced with total
counts not to exceed log 10 /g 5.00. In a study of 48 meat pies, 84% had an APC log 10 < 5,
38 whereas
in another study of 188 meat pies, 93% had counts log 10 < 5.00.
25 Accordingly, a microbiological
criterion of log 10 5.00 seems attainable for such products (see Chapter 21 for further information on
microbiological standards and criteria). In a study of 1,290 frozen tuna pot pies, the geometric mean
APC at 35
◦ C was log 10 3.20, whereas at 30
◦ C it was log 10 /g 3.38.
66 Coliforms averaged 5/g, E. coli
<3/g, and S. aureus <10/g (Table 9–1).
SUGARS, CANDIES, AND SPICES
These products rarely undergo microbial spoilage if properly prepared, processed, and stored,
primarily because of the lack of sufficient moisture for growth. Both cane and beet sugars may be
expected to contain microorganisms. The important bacterial contaminants are members of the genera
Bacillus, Paenibacillus, and Clostridium, which sometimes cause trouble in the canning industry (see
Chapter 17). If sugars are stored under conditions of extremely high humidity, growth of some of
these organisms is possible, usually at the exposed surfaces. The successful growth of these organisms
depends, of course, on their getting an adequate supply of moisture and essential nutrients other
than carbohydrates. “Torula” and osmophilic strains of Saccharomyces (Zygosaccharomyces spp.)
have been reported to cause trouble in high-moisture sugars. These organisms have been reported to
cause inversion of sugar. One of the most troublesome organisms in sugar refineries is Leuconostoc
mesenteroides. This organism hydrolyzes sucrose and synthesizes a glucose polymer referred to as
dextran. This gummy and slimy polymer sometimes clogs the lines and pipes through which sucrose
solutions pass.
still warm. Homemade breads may undergo a type of spoilage known as ropiness, which is caused
by the growth and amylase production of certain strains of Bacillus subtilis (B. mesentericus). The
ropiness may be seen as stringiness by carefully breaking a batch of dough into two parts. The source of
the organisms is flour, and their growth is favored by holding the dough for sufficient periods of time at
suitable temperatures. In a recent study, part-baked soda bread (pH 7–9) stored at room temperature
developed ropiness after 2 days, and three species were isolated from the ropy product: B. subtilis, B.
pumilus, and B. licheniformis.
34
Cakes of all types rarely undergo bacterial spoilage due to their unusually high concentrations of
sugars, which restrict the availability of water. The most common form of spoilage displayed by these
products is moldiness. Common sources of spoilage molds are any and all cake ingredients, especially
sugar, nuts, and spices. Although the baking process is generally sufficient to destroy these organisms,
many are added in icings, meringues, toppings, and so forth. Also, molds may enter baked cakes from
handling and from the air. Growth of molds on the surface of cakes is favored by conditions of high
humidity. On some fruitcakes, growth often originates underneath nuts and fruits if they are placed on
the surface of such products after baking. Continued growth of molds on breads and cakes results in
a hardening of the products.
FROZEN MEAT PIES
The microbiological quality of frozen meat pies has steadily improved since these products were first
marketed. Any and all of the ingredients added may increase the total number of organisms, and the
total count of the finished product may be taken to reflect the overall quality of ingredients, handling,
and storage. Many investigators have suggested that these products should be produced with total
counts not to exceed log 10 /g 5.00. In a study of 48 meat pies, 84% had an APC log 10 < 5,
38 whereas
in another study of 188 meat pies, 93% had counts log 10 < 5.00.
25 Accordingly, a microbiological
criterion of log 10 5.00 seems attainable for such products (see Chapter 21 for further information on
microbiological standards and criteria). In a study of 1,290 frozen tuna pot pies, the geometric mean
APC at 35
◦ C was log 10 3.20, whereas at 30
◦ C it was log 10 /g 3.38.
66 Coliforms averaged 5/g, E. coli
<3/g, and S. aureus <10/g (Table 9–1).
SUGARS, CANDIES, AND SPICES
These products rarely undergo microbial spoilage if properly prepared, processed, and stored,
primarily because of the lack of sufficient moisture for growth. Both cane and beet sugars may be
expected to contain microorganisms. The important bacterial contaminants are members of the genera
Bacillus, Paenibacillus, and Clostridium, which sometimes cause trouble in the canning industry (see
Chapter 17). If sugars are stored under conditions of extremely high humidity, growth of some of
these organisms is possible, usually at the exposed surfaces. The successful growth of these organisms
depends, of course, on their getting an adequate supply of moisture and essential nutrients other
than carbohydrates. “Torula” and osmophilic strains of Saccharomyces (Zygosaccharomyces spp.)
have been reported to cause trouble in high-moisture sugars. These organisms have been reported to
cause inversion of sugar. One of the most troublesome organisms in sugar refineries is Leuconostoc
mesenteroides. This organism hydrolyzes sucrose and synthesizes a glucose polymer referred to as
dextran. This gummy and slimy polymer sometimes clogs the lines and pipes through which sucrose
solutions pass.