Spoilage of Specific Food Groups ◾ 265
Grains and Seeds
Grains and seeds normally have 10%–12% moisture, which lowers the A W to approximately ≤0.6
and thus inhibits microbial growth. In cereal grains, during harvesting, processing, and storage,
if the A W increases above 0.6, some molds can grow. Some species of storage fungi from genera
Aspergillus, Penicillium, and Rhizopus can cause spoilage of high-moisture grains. Many types
of lentils, beans, and seeds (alfalfa) are germinated and used as ready-to-eat products. During
storage, Gram-positive and Gram-negative bacteria, yeasts, and molds can grow and produce
off-flavor.
Refrigerated Dough
Refrigerated dough (for biscuits, rolls, and pizzas) is susceptible to spoilage (gas formation) from
the growth of psychrotrophic heterolactic acid bacterial species of Lactobacillus and Leuconostoc.
Rapid CO 2 production can blow the containers, especially when the storage temperature increases
to 10°C and above.
Breads
The A W of breads is normally low enough (0.75–0.9) to prevent growth of bacteria. However,
some molds (bread molds: Rhizopus stolonifer) can grow, especially if moisture is released because
of starch crystallization during storage. Molds are killed during baking; however, spores can get in
from air and equipment following baking. When breads are frozen, they may contain ice crystals
in the bags. Following thawing, some portions can absorb enough moisture for yeasts and bacteria
to grow and cause spoilage (sour taste, off-flavor). A specific type of bread spoilage, designated as
ropiness and characterized by a soft, stringy, brown mass with fruity odor, is caused by the growth
of some mucoid variants of Bac. subtilis. The spores, coming from flour or equipment, survive baking and then germinate and grow inside within 1–2 days. They also produce extracellular amylases
and proteases and break down the bread structure. High moisture inside the bread, slow cooling,
and pH above 5.0 favor ropiness.
Pastas
Pastas can be spoiled by microorganisms before drying because of improper manufacturing practices. Dry pastas do not favor microbial growth. However, soft pastas can be spoiled by bacteria,
yeasts, and molds. Anaerobic packing and refrigeration storage can prevent mold growth and slow
down growth of yeasts and psychrotrophic anaerobic and facultative anaerobic bacteria. Suitable
preservatives can be used to prevent their growth.
Pastries
Pastries include cakes and baked shells filled with custard, cream, or sauces. They can be spoiled
by microorganisms coming with the ingredients that are added after baking, such as icing, nuts,
toppings, and cream. Most products, because of low A W , allow only molds to grow. However, some
materials used as fillings may have high A W , which allows for bacterial growth.
Grains and Seeds
Grains and seeds normally have 10%–12% moisture, which lowers the A W to approximately ≤0.6
and thus inhibits microbial growth. In cereal grains, during harvesting, processing, and storage,
if the A W increases above 0.6, some molds can grow. Some species of storage fungi from genera
Aspergillus, Penicillium, and Rhizopus can cause spoilage of high-moisture grains. Many types
of lentils, beans, and seeds (alfalfa) are germinated and used as ready-to-eat products. During
storage, Gram-positive and Gram-negative bacteria, yeasts, and molds can grow and produce
off-flavor.
Refrigerated Dough
Refrigerated dough (for biscuits, rolls, and pizzas) is susceptible to spoilage (gas formation) from
the growth of psychrotrophic heterolactic acid bacterial species of Lactobacillus and Leuconostoc.
Rapid CO 2 production can blow the containers, especially when the storage temperature increases
to 10°C and above.
Breads
The A W of breads is normally low enough (0.75–0.9) to prevent growth of bacteria. However,
some molds (bread molds: Rhizopus stolonifer) can grow, especially if moisture is released because
of starch crystallization during storage. Molds are killed during baking; however, spores can get in
from air and equipment following baking. When breads are frozen, they may contain ice crystals
in the bags. Following thawing, some portions can absorb enough moisture for yeasts and bacteria
to grow and cause spoilage (sour taste, off-flavor). A specific type of bread spoilage, designated as
ropiness and characterized by a soft, stringy, brown mass with fruity odor, is caused by the growth
of some mucoid variants of Bac. subtilis. The spores, coming from flour or equipment, survive baking and then germinate and grow inside within 1–2 days. They also produce extracellular amylases
and proteases and break down the bread structure. High moisture inside the bread, slow cooling,
and pH above 5.0 favor ropiness.
Pastas
Pastas can be spoiled by microorganisms before drying because of improper manufacturing practices. Dry pastas do not favor microbial growth. However, soft pastas can be spoiled by bacteria,
yeasts, and molds. Anaerobic packing and refrigeration storage can prevent mold growth and slow
down growth of yeasts and psychrotrophic anaerobic and facultative anaerobic bacteria. Suitable
preservatives can be used to prevent their growth.
Pastries
Pastries include cakes and baked shells filled with custard, cream, or sauces. They can be spoiled
by microorganisms coming with the ingredients that are added after baking, such as icing, nuts,
toppings, and cream. Most products, because of low A W , allow only molds to grow. However, some
materials used as fillings may have high A W , which allows for bacterial growth.