44 ◾ Fundamental Food Microbiology
bacterial growth. However, if the storage temperature is favorable, they can grow in yolk that is
rich in nutrients and has a pH of 7.0. Pasteurization of liquid egg has been designed to destroy
pathogens (especially Salmonella) and other Gram-negative rods. Thermoduric bacteria, namely
Micrococcus, Enterococcus, and Bacillus, present in the raw liquid egg survive pasteurization.
Fish and Shellfish
This group includes finfish, crustaceans (shrimp, lobster, crabs), and mollusks (oysters, mussels,
clams, scallops) harvested from aquatic environments (marine and freshwater). 8 Fish and shellfish
are harvested from natural sources and aquacultures. In general, they are rich in protein and
nonprotein nitrogenous compounds; their fat content varies with type and season. Except for mollusks, they are very low in carbohydrates; mollusks contain about 3% glycogen.
The microbial population in these products varies greatly with the pollution level and temperature of the water. Bacteria from many groups, as well as viruses, parasites, and protozoa and
helminths, can be present in the raw materials. Muscles of fish and shellfish are sterile, but scales,
gills, and intestines harbor microorganisms. Finfish and crustaceans can have 10 3–8 bacterial
cells/g. During feeding, mollusks filter large volumes of water and can thus concentrate bacteria
and viruses. Products harvested from marine environments can have halophilic vibrios as well as
Pseudomonas, Alteromonas, Flavobacterium, Enterococcus, Micrococcus, coliforms, and pathogens,
such as Vib. parahaemolyticus, Vib. vulnificus, Shigella spp. and Clo. botulinum type E. Freshwater
fish generally have Pseudomonas, Flavobacterium, Enterococcus, Micrococcus, Bacillus, and coliforms. Fish and shellfish harvested from water polluted with human and animal waste can contain Salmonella, Shigella, Clo. perfringens, Vib. cholerae, and hepatitis A and norovirus. They can
also contain opportunistic pathogens, such as Aeromonas hydrophila and Plesiomonas shigelloides.
The harvesting of seafoods, especially shellfish, is controlled by regulatory agencies in the United
States. Water with high coliform populations is forbidden to harvest. Protozoan species, such as
Giardia spp., and large, worm-like parasites, such as nematodes, trematodes, and cestodes, are also
associated with seafoods (see Chapter 28).
If harvested from polluted water, microorganisms can grow rapidly in fish and crustaceans
because of high A W , high pH of the tissue, and availability of large amounts of nonprotein nitrogenous compounds. As many of the bacterial species are psychrotrophs, they can grow at refrigerated temperatures. Pathogens can remain viable for a long time during storage. Microbial loads are
greatly reduced during their subsequent heat processing to produce different products.
Vegetables, Fruits, and nuts
Vegetables include edible plant components, such as leaves (i.e., spinach, lettuce, cilantro), stalks
(i.e., celery, sprouts), roots, tubers, bulbs, and flowers. In general, they are relatively high in carbohydrates, with pH values of 5.0–7.0. Thus, different types of bacteria, yeasts, and molds can grow
if other conditions are favorable. 9 Fruits are high in carbohydrates and have a pH of 4.5 or below
because of the presence of organic acids, and some also have antimicrobial essential oils. Nuts can
be from the ground (peanuts) or from trees (pecans) and have protective shells and low A W (0.7).
They are converted to nutmeats for further use or to products, such as peanut butter.
Fruits and vegetables are perceived as healthy, and these are consumed raw or minimally processed. However, recently, these products have been responsible for numerous fatal outbreaks,
bacterial growth. However, if the storage temperature is favorable, they can grow in yolk that is
rich in nutrients and has a pH of 7.0. Pasteurization of liquid egg has been designed to destroy
pathogens (especially Salmonella) and other Gram-negative rods. Thermoduric bacteria, namely
Micrococcus, Enterococcus, and Bacillus, present in the raw liquid egg survive pasteurization.
Fish and Shellfish
This group includes finfish, crustaceans (shrimp, lobster, crabs), and mollusks (oysters, mussels,
clams, scallops) harvested from aquatic environments (marine and freshwater). 8 Fish and shellfish
are harvested from natural sources and aquacultures. In general, they are rich in protein and
nonprotein nitrogenous compounds; their fat content varies with type and season. Except for mollusks, they are very low in carbohydrates; mollusks contain about 3% glycogen.
The microbial population in these products varies greatly with the pollution level and temperature of the water. Bacteria from many groups, as well as viruses, parasites, and protozoa and
helminths, can be present in the raw materials. Muscles of fish and shellfish are sterile, but scales,
gills, and intestines harbor microorganisms. Finfish and crustaceans can have 10 3–8 bacterial
cells/g. During feeding, mollusks filter large volumes of water and can thus concentrate bacteria
and viruses. Products harvested from marine environments can have halophilic vibrios as well as
Pseudomonas, Alteromonas, Flavobacterium, Enterococcus, Micrococcus, coliforms, and pathogens,
such as Vib. parahaemolyticus, Vib. vulnificus, Shigella spp. and Clo. botulinum type E. Freshwater
fish generally have Pseudomonas, Flavobacterium, Enterococcus, Micrococcus, Bacillus, and coliforms. Fish and shellfish harvested from water polluted with human and animal waste can contain Salmonella, Shigella, Clo. perfringens, Vib. cholerae, and hepatitis A and norovirus. They can
also contain opportunistic pathogens, such as Aeromonas hydrophila and Plesiomonas shigelloides.
The harvesting of seafoods, especially shellfish, is controlled by regulatory agencies in the United
States. Water with high coliform populations is forbidden to harvest. Protozoan species, such as
Giardia spp., and large, worm-like parasites, such as nematodes, trematodes, and cestodes, are also
associated with seafoods (see Chapter 28).
If harvested from polluted water, microorganisms can grow rapidly in fish and crustaceans
because of high A W , high pH of the tissue, and availability of large amounts of nonprotein nitrogenous compounds. As many of the bacterial species are psychrotrophs, they can grow at refrigerated temperatures. Pathogens can remain viable for a long time during storage. Microbial loads are
greatly reduced during their subsequent heat processing to produce different products.
Vegetables, Fruits, and nuts
Vegetables include edible plant components, such as leaves (i.e., spinach, lettuce, cilantro), stalks
(i.e., celery, sprouts), roots, tubers, bulbs, and flowers. In general, they are relatively high in carbohydrates, with pH values of 5.0–7.0. Thus, different types of bacteria, yeasts, and molds can grow
if other conditions are favorable. 9 Fruits are high in carbohydrates and have a pH of 4.5 or below
because of the presence of organic acids, and some also have antimicrobial essential oils. Nuts can
be from the ground (peanuts) or from trees (pecans) and have protective shells and low A W (0.7).
They are converted to nutmeats for further use or to products, such as peanut butter.
Fruits and vegetables are perceived as healthy, and these are consumed raw or minimally processed. However, recently, these products have been responsible for numerous fatal outbreaks,