Taxonomy, Role, and Significance of Microorganisms in Foods
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hyaline and red or orange, and they may form arthrospores. They have been found on plants, in soils,
on strawberries and other fruits, marine fish, shrimp, and fresh ground beef.
Debaryomyces. These ascosporogenous yeasts sometimes produce a pseudomycelium and reproduce
by multilateral budding. They are one of the two most prevalent yeast genera in dairy products.
D. hansenii represents what was once D. subglobosus and Torulaspora hansenii, and it is the most
prevalent foodborne species. It can grow in 24% NaCl and at an a w as low as 0.65. It forms slime on
wieners, grows in brines and on cheeses, and causes spoilage of orange juice concentrate and yogurt.
Hanseniaspora. These are apiculate yeasts whose anamorphs are Kloeckera spp. They exhibit bipolar
budding, and, consequently, lemonshaped cells are produced. The asci contain two to four hat-shaped
spores. Sugars are fermented, and they can be found on a variety of foods, especially figs, tomatoes,
strawberries, citrus fruits, and the cacao bean fermentation.
Issatchenkia. Members of this genus produce pseudomycelia and multiply by multilateral budding.
Some species once in the genus Pichia have been placed here. The teleomorph of Candida krusei
is I. orientalis. They typically form pellicles in liquid media. They contain coenzyme Q-7 and are
prevalent on a wide variety of foods.
Kluyveromyces (Fabospora). These ascospore-forming yeasts reproduce by multilateral budding, and
the spores are spherical. K. marxianus now includes the former K. fragilis, K. lactis, K. bulgaricus,
Saccharomyces lactis, and S. fragilis. K. marxianus is one of the two most prevalent yeasts in dairy
products. Kluyveromyces spp. produce β-galactosidase and are vigorous fermenters of sugars, including lactose. K. marxianus contains coenzyme Q-6 and is involved in the fermentation of kumiss. It is
also used for lactase production from whey and as the organism of choice for producing yeast cells
from whey. They are found on a wide variety of fruits, and K. marxianus causes cheese spoilage.
Pichia. This is the largest genus of true yeasts. They reproduce by multilateral budding, and the asci
usually contain four spheroidal, hat- or saturn-shaped spores. Pseudomycelia and arthrospores may
be formed. Some of the hat-shaped spore formers may be Williopsis spp., and some of the former
species are now classified in the genus Debaryomyces. P. guilliermondii is the perfect state of Candida
guillermondii. The anamorph of P. membranaefaciens is Candida valida. Pichia spp. typically form
films on liquid media and are known to be important in producing indigenous foods in various parts
of the world. Some have been found on fresh fish and shrimp, and they are known to grow in olive
brines and to cause spoilage of pickles and sauerkraut.
Rhodotorula. These yeasts are anamorphs of Basidiomycetes. The teliospore producers are in the
genus Rhodosporidium. They reproduce by multilateral budding and are nonfermenters. R. glutinis
and R. mucilaginosa are the two most prevalent species in foods. They produce pink to red pigments,
and most are orange or salmon pink in color. The genus contains many psychrotrophic species/strains
that are found on fresh poultry, shrimp, fish, and beef. Some grow on the surface of butter.
Saccharomyces. These ascosporogenous yeasts multiply by multilateral budding and produce spherical spores in asci. They are diploid and do not ferment lactose. Those once classified as S. bisporus
and S. rouxii are now in the genus Zygosaccharomyces, and the former S. rosei is now in the genus
Torulaspora. All bakers’, brewers’, wine, and champagne yeasts are S. cerevisiae. They are found in
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hyaline and red or orange, and they may form arthrospores. They have been found on plants, in soils,
on strawberries and other fruits, marine fish, shrimp, and fresh ground beef.
Debaryomyces. These ascosporogenous yeasts sometimes produce a pseudomycelium and reproduce
by multilateral budding. They are one of the two most prevalent yeast genera in dairy products.
D. hansenii represents what was once D. subglobosus and Torulaspora hansenii, and it is the most
prevalent foodborne species. It can grow in 24% NaCl and at an a w as low as 0.65. It forms slime on
wieners, grows in brines and on cheeses, and causes spoilage of orange juice concentrate and yogurt.
Hanseniaspora. These are apiculate yeasts whose anamorphs are Kloeckera spp. They exhibit bipolar
budding, and, consequently, lemonshaped cells are produced. The asci contain two to four hat-shaped
spores. Sugars are fermented, and they can be found on a variety of foods, especially figs, tomatoes,
strawberries, citrus fruits, and the cacao bean fermentation.
Issatchenkia. Members of this genus produce pseudomycelia and multiply by multilateral budding.
Some species once in the genus Pichia have been placed here. The teleomorph of Candida krusei
is I. orientalis. They typically form pellicles in liquid media. They contain coenzyme Q-7 and are
prevalent on a wide variety of foods.
Kluyveromyces (Fabospora). These ascospore-forming yeasts reproduce by multilateral budding, and
the spores are spherical. K. marxianus now includes the former K. fragilis, K. lactis, K. bulgaricus,
Saccharomyces lactis, and S. fragilis. K. marxianus is one of the two most prevalent yeasts in dairy
products. Kluyveromyces spp. produce β-galactosidase and are vigorous fermenters of sugars, including lactose. K. marxianus contains coenzyme Q-6 and is involved in the fermentation of kumiss. It is
also used for lactase production from whey and as the organism of choice for producing yeast cells
from whey. They are found on a wide variety of fruits, and K. marxianus causes cheese spoilage.
Pichia. This is the largest genus of true yeasts. They reproduce by multilateral budding, and the asci
usually contain four spheroidal, hat- or saturn-shaped spores. Pseudomycelia and arthrospores may
be formed. Some of the hat-shaped spore formers may be Williopsis spp., and some of the former
species are now classified in the genus Debaryomyces. P. guilliermondii is the perfect state of Candida
guillermondii. The anamorph of P. membranaefaciens is Candida valida. Pichia spp. typically form
films on liquid media and are known to be important in producing indigenous foods in various parts
of the world. Some have been found on fresh fish and shrimp, and they are known to grow in olive
brines and to cause spoilage of pickles and sauerkraut.
Rhodotorula. These yeasts are anamorphs of Basidiomycetes. The teliospore producers are in the
genus Rhodosporidium. They reproduce by multilateral budding and are nonfermenters. R. glutinis
and R. mucilaginosa are the two most prevalent species in foods. They produce pink to red pigments,
and most are orange or salmon pink in color. The genus contains many psychrotrophic species/strains
that are found on fresh poultry, shrimp, fish, and beef. Some grow on the surface of butter.
Saccharomyces. These ascosporogenous yeasts multiply by multilateral budding and produce spherical spores in asci. They are diploid and do not ferment lactose. Those once classified as S. bisporus
and S. rouxii are now in the genus Zygosaccharomyces, and the former S. rosei is now in the genus
Torulaspora. All bakers’, brewers’, wine, and champagne yeasts are S. cerevisiae. They are found in