Fundamental Food Microbiology, Third Edition - Fuad Fathir

SPOILAGE OF SPECIFIC FOOD GROUPS 281
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, Grampositive
and Gram-negative bacteria, yeasts, and molds can grow and produce offflavor.
B. Refrigerated Dough
Refrigerated dough (for biscuits, rolls, and pizza) 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.
C. Breads
The A w of breads is normally low enough (0.75 to 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 to 2 d. 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.
D. 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.
E. 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.
\