Normal Microbiological Quality of Foods and Its Significance ◾ 45
and their association with outbreaks is on the rise. 9 Microorganisms in vegetables can come from
several sources, such as soil, water, air, wild or domestic animals, insects, birds, or equipment, and
vary with the types of vegetables. A leafy vegetable has more microorganisms from the air, whereas
a tuber has more from the soil. Microbial levels and types in these products also vary greatly,
depending on environmental conditions and conditions of farming and harvesting. Generally,
vegetables have 10 3–5 microorganisms/cm 2 or 10 4–7 /g. Some of the predominant bacterial types are
lactic acid bacteria, Corynebacterium, Enterobacter, Proteus, Pseudomonas, Micrococcus, Enterococcus,
and spore formers. They also have different types of molds, such as Alternaria, Fusarium, and
Aspergillus. Vegetables can have enteric pathogens, especially if animal and human wastes and polluted water are used for fertilization and irrigation. They include Lis. monocytogenes, Salmonella,
Shigella, pathogenic Eschrichia coli (O157:H7 and O104:H4), Campylobacter, Clo. botulinum, and
Clo. perfringens. They can also have pathogenic protozoa and parasites (Cyclospora, Cystoisospora,
Giardia). If the vegetables are damaged, then plant pathogens (e.g., Erwinia) can also predominate. Many of the microorganisms can cause different types of spoilage (different types of rot) of
raw products. Pathogens can grow in plant products and cause foodborne diseases (e.g., listeriosis
or botulism). Lactic acid bacteria have important roles in the natural fermentation of vegetables
(e.g., sauerkraut). Different methods used to process vegetables and vegetable products greatly
reduce the microbial population.
Fruits, because of their high carbohydrate content and low pH, favor the growth of different
types of molds, yeasts, and lactic acid bacteria. Microorganisms generally come from air, soil,
insects, and harvesting equipment. In general, microbial populations are 10 3–6 /g. Improperly harvested and processed fruits can have pathogens that survive, grow, and cause foodborne disease.
Molds, yeasts, and bacteria can cause different types of spoilage. Natural flora, especially yeasts in
fruits, can be important in alcohol fermentation.
Microorganisms enter nuts from the soil (peanuts) and air (tree nuts). During processing, air,
equipment, and water can also be the sources. Nuts are protected by shells, but damage to the shell
can facilitate microbial contamination. Raw nuts and nutmeats can have 10 3–4 microorganisms/g
with Bacillus and Clostridium spores, Leuconostoc, Pseudomonas, and Micrococcus predominating.
Because of a low A W , bacteria do not grow in the products. However, when used as ingredients,
they can cause microbiological problems in the products. Molds can grow in nuts and nutmeats
and produce mycotoxins (from toxin-producing strains, such as aflatoxins by Aspergillus flavus).
Cereal, Starches, and Gums
Cereal includes grains, flour, meals, breakfast cereals, pasta, baked products, dry mixes, and frozen and refrigerated products of cereal grains (also beans and lentils). Starches include flours of
cereals (e.g., corn, rice), tapioca (from a plant), potatoes, and other tubers. Gums are used as
stabilizers, gelling agents, and films and are obtained from plants, seaweeds, and microorganisms
(e.g., tragacanth, pectin, xanthan, agar, and carrageenan) and as modified compounds (e.g., carboxymethyl cellulose). They are rich in amylose and amylopectin but can also have simple sugars
(e.g., in grains) and protein (e.g., in lentils). Microbial sources are mainly the soil, air, insects,
birds, and equipment.
Unprocessed products (grains) may contain high bacterial levels (aerobic plate count ≤10 4 /g,
coliform ≤10 2 /g, yeasts and molds ≤10 3 /g). They may also contain mycotoxins produced by toxicogenic molds. Processed products may also contain a wide variety of yeasts, molds, and bacteria. Flours and starches may have higher microbial counts, similar to those of grains, whereas
and their association with outbreaks is on the rise. 9 Microorganisms in vegetables can come from
several sources, such as soil, water, air, wild or domestic animals, insects, birds, or equipment, and
vary with the types of vegetables. A leafy vegetable has more microorganisms from the air, whereas
a tuber has more from the soil. Microbial levels and types in these products also vary greatly,
depending on environmental conditions and conditions of farming and harvesting. Generally,
vegetables have 10 3–5 microorganisms/cm 2 or 10 4–7 /g. Some of the predominant bacterial types are
lactic acid bacteria, Corynebacterium, Enterobacter, Proteus, Pseudomonas, Micrococcus, Enterococcus,
and spore formers. They also have different types of molds, such as Alternaria, Fusarium, and
Aspergillus. Vegetables can have enteric pathogens, especially if animal and human wastes and polluted water are used for fertilization and irrigation. They include Lis. monocytogenes, Salmonella,
Shigella, pathogenic Eschrichia coli (O157:H7 and O104:H4), Campylobacter, Clo. botulinum, and
Clo. perfringens. They can also have pathogenic protozoa and parasites (Cyclospora, Cystoisospora,
Giardia). If the vegetables are damaged, then plant pathogens (e.g., Erwinia) can also predominate. Many of the microorganisms can cause different types of spoilage (different types of rot) of
raw products. Pathogens can grow in plant products and cause foodborne diseases (e.g., listeriosis
or botulism). Lactic acid bacteria have important roles in the natural fermentation of vegetables
(e.g., sauerkraut). Different methods used to process vegetables and vegetable products greatly
reduce the microbial population.
Fruits, because of their high carbohydrate content and low pH, favor the growth of different
types of molds, yeasts, and lactic acid bacteria. Microorganisms generally come from air, soil,
insects, and harvesting equipment. In general, microbial populations are 10 3–6 /g. Improperly harvested and processed fruits can have pathogens that survive, grow, and cause foodborne disease.
Molds, yeasts, and bacteria can cause different types of spoilage. Natural flora, especially yeasts in
fruits, can be important in alcohol fermentation.
Microorganisms enter nuts from the soil (peanuts) and air (tree nuts). During processing, air,
equipment, and water can also be the sources. Nuts are protected by shells, but damage to the shell
can facilitate microbial contamination. Raw nuts and nutmeats can have 10 3–4 microorganisms/g
with Bacillus and Clostridium spores, Leuconostoc, Pseudomonas, and Micrococcus predominating.
Because of a low A W , bacteria do not grow in the products. However, when used as ingredients,
they can cause microbiological problems in the products. Molds can grow in nuts and nutmeats
and produce mycotoxins (from toxin-producing strains, such as aflatoxins by Aspergillus flavus).
Cereal, Starches, and Gums
Cereal includes grains, flour, meals, breakfast cereals, pasta, baked products, dry mixes, and frozen and refrigerated products of cereal grains (also beans and lentils). Starches include flours of
cereals (e.g., corn, rice), tapioca (from a plant), potatoes, and other tubers. Gums are used as
stabilizers, gelling agents, and films and are obtained from plants, seaweeds, and microorganisms
(e.g., tragacanth, pectin, xanthan, agar, and carrageenan) and as modified compounds (e.g., carboxymethyl cellulose). They are rich in amylose and amylopectin but can also have simple sugars
(e.g., in grains) and protein (e.g., in lentils). Microbial sources are mainly the soil, air, insects,
birds, and equipment.
Unprocessed products (grains) may contain high bacterial levels (aerobic plate count ≤10 4 /g,
coliform ≤10 2 /g, yeasts and molds ≤10 3 /g). They may also contain mycotoxins produced by toxicogenic molds. Processed products may also contain a wide variety of yeasts, molds, and bacteria. Flours and starches may have higher microbial counts, similar to those of grains, whereas