Characteristics of Predominant Microorganisms in Food ◾ 19
4. Geotrichum. Members are septate and form rectangular arthrospores. They grow, forming
a yeast-like cottony, creamy colony. They establish easily in equipment and often grow on
dairy products (dairy mold). Species: Geotrichum candidum.
5. Mucor. It is widely distributed. Members have nonseptate hyphae and produce sporangiophores. They produce cottony colonies. Some species are used in food Mucor rouxii.
6. Penicillium. It is widely distributed and contains many species. Members have septate hyphae
and form conidiophores on a blue-green, brush-like conidia head (Figure 2.2). Some species
are used in food production, such as Penicillium roquefortii and Pen. camembertii in cheese.
Many species cause fungal rot in fruits and vegetables. They also cause spoilage of grains,
breads, and meat. Some strains produce mycotoxins (e.g., Ochratoxin A).
7. Rhizopus. Hyphae are aseptate and form sporangiophores in sporangium. They cause spoilage of many fruits and vegetables. Rhizopus stolonifer is the common black bread mold.
Important Yeast Genera
Yeasts are important in food because of their ability to cause spoilage. Many are also used in
food bioprocessing. Some are used to produce food additives. Several important genera are briefly
described next. 4
1. Saccharomyces. Cells are round, oval, or elongated. It is the most important genus and contains heterogenous groups (Figure 2.2). Saccharomyces cerevisiae variants are used in baking
for leavening bread and in alcoholic fermentation. They also cause spoilage of food, producing alcohol and CO 2 .
2. Pichia. Cells are oval to cylindrical and form pellicles in beer, wine, and brine to cause spoilage. Some are also used in oriental food fermentation. Species: Pichia membranaefaciens.
3. Rhodotorula. They are pigment-forming yeasts and can cause discoloration of foods such as
meat, fish, and sauerkraut. Species: Rhodotorula glutinis.
4. Torulopsis. Cells are spherical to oval. They cause spoilage of milk because they can ferment
lactose (e.g., Torulopsis versatilis). They also spoil fruit juice concentrates and acid foods.
5. Candida. Many species spoil foods with high acid, salt, and sugar and form pellicles on the
surface of liquids. Some can cause rancidity in butter and dairy products (e.g., Candida
lipolyticum).
6. Zygosaccharomyces. These cause spoilage of high-acid foods, such as sauces, ketchups, pickles,
mustards, mayonnaise, and salad dressings, especially those with less acid and less salt and
sugar (e.g., Zygosaccharomyces bailii).
Foodborne Protozoan Parasites
Protozoan parasites 8,9 are eukaryotic cells and some are associated with water and foodborne
outbreaks. Often wild animals, livestock, pets, or even humans carry these parasites and serve
as a source. Contaminated soil and irrigation water are known causes for the contamination of
fresh produce. The major organisms are Giardia (Gia. lamblia), Cryptosporidium (Cry. parvum),
Cyclospora (Cyc. cayetanensis), Cystoisospora (Cys. belli), and Toxoplasma (Tox. gondii). Members of
these organisms generally require two hosts to complete their life cycle. They produce an infective
oocyst that generally contains two to four sporozoites. Both asexual and sexual reproduction allow
4. Geotrichum. Members are septate and form rectangular arthrospores. They grow, forming
a yeast-like cottony, creamy colony. They establish easily in equipment and often grow on
dairy products (dairy mold). Species: Geotrichum candidum.
5. Mucor. It is widely distributed. Members have nonseptate hyphae and produce sporangiophores. They produce cottony colonies. Some species are used in food Mucor rouxii.
6. Penicillium. It is widely distributed and contains many species. Members have septate hyphae
and form conidiophores on a blue-green, brush-like conidia head (Figure 2.2). Some species
are used in food production, such as Penicillium roquefortii and Pen. camembertii in cheese.
Many species cause fungal rot in fruits and vegetables. They also cause spoilage of grains,
breads, and meat. Some strains produce mycotoxins (e.g., Ochratoxin A).
7. Rhizopus. Hyphae are aseptate and form sporangiophores in sporangium. They cause spoilage of many fruits and vegetables. Rhizopus stolonifer is the common black bread mold.
Important Yeast Genera
Yeasts are important in food because of their ability to cause spoilage. Many are also used in
food bioprocessing. Some are used to produce food additives. Several important genera are briefly
described next. 4
1. Saccharomyces. Cells are round, oval, or elongated. It is the most important genus and contains heterogenous groups (Figure 2.2). Saccharomyces cerevisiae variants are used in baking
for leavening bread and in alcoholic fermentation. They also cause spoilage of food, producing alcohol and CO 2 .
2. Pichia. Cells are oval to cylindrical and form pellicles in beer, wine, and brine to cause spoilage. Some are also used in oriental food fermentation. Species: Pichia membranaefaciens.
3. Rhodotorula. They are pigment-forming yeasts and can cause discoloration of foods such as
meat, fish, and sauerkraut. Species: Rhodotorula glutinis.
4. Torulopsis. Cells are spherical to oval. They cause spoilage of milk because they can ferment
lactose (e.g., Torulopsis versatilis). They also spoil fruit juice concentrates and acid foods.
5. Candida. Many species spoil foods with high acid, salt, and sugar and form pellicles on the
surface of liquids. Some can cause rancidity in butter and dairy products (e.g., Candida
lipolyticum).
6. Zygosaccharomyces. These cause spoilage of high-acid foods, such as sauces, ketchups, pickles,
mustards, mayonnaise, and salad dressings, especially those with less acid and less salt and
sugar (e.g., Zygosaccharomyces bailii).
Foodborne Protozoan Parasites
Protozoan parasites 8,9 are eukaryotic cells and some are associated with water and foodborne
outbreaks. Often wild animals, livestock, pets, or even humans carry these parasites and serve
as a source. Contaminated soil and irrigation water are known causes for the contamination of
fresh produce. The major organisms are Giardia (Gia. lamblia), Cryptosporidium (Cry. parvum),
Cyclospora (Cyc. cayetanensis), Cystoisospora (Cys. belli), and Toxoplasma (Tox. gondii). Members of
these organisms generally require two hosts to complete their life cycle. They produce an infective
oocyst that generally contains two to four sporozoites. Both asexual and sexual reproduction allow