268 ◾ Fundamental Food Microbiology
surface and produce undesirable color and flavor defects in the products. Anaerobic packaging
greatly reduces this problem.
Fermented Vegetable and Fruit Products
Many types of vegetables are fermented, among which cucumber pickles and sauerkraut are produced in large volumes. In salt stock pickles containing approximately 15% salt, yeasts and halophilic bacteria can grow, especially if the acidity is not sufficient. Dill pickles with low salt (<5%)
can have a bloating defect from CO 2 production by yeasts, heterofermentative lactic acid bacteria,
and coliforms, especially if the desirable bacteria associated with fermentation do not grow properly. Candida, Torulopsis, and Saccharomyces spp. are often the causative yeasts. Sweet and sour
pickles preserved with sugar and vinegar can be spoiled from the growth of yeasts and lactic acid
bacteria, especially when the acid level is not sufficient. Sauerkraut can be spoiled from the growth
of yeasts and molds if the air is not excluded during fermentation of cabbage (see Chapter 15).
Failure of lactic acid bacteria to grow rapidly and in proper sequence can lead to low acid production. Under this condition, coliforms and other Gram-negative bacteria can multiply to produce
undesirable flavor, texture, and color defects. Olives are fermented for a long time and are susceptible to many types of spoilage. The most common problem is gassiness (bloating) resulting from
CO 2 production by heterofermentative lactic acid bacteria, coliforms, and yeasts. Softening of
texture can be caused by pectinases of yeasts (Rhodotorula spp.).
Fermented Beverages
Wines can support the growth of film yeasts and acetic acid bacteria (Acetobacter and Gluconobacter)
under aerobic conditions. Film yeasts oxidize alcohol and organic acids and form a surface pellicle,
whereas acetic acid bacteria oxidize alcohol to acetic acid and CO 2 . Under anaerobic conditions,
several lactic acid bacteria (e.g., Lactobacillus, Leuconostoc, and Pediococcus spp.) can grow in wine.
Some heterofermentative Lactobacillus spp. can ferment glucose and fructose and increase the
acidity of wine, producing a defect called tourne spoilage (by Lab. brevis, Lab. buchneri). They
can also produce cloudiness and a mousy odor. Some Leuconostoc spp. can produce sliminess and
cloudiness. Oenococcus oenos can convert malic acid to lactic acid and CO 2 and reduce the acidity
of wine. Sometimes, this malolactic fermentation is used advantageously to reduce the sourness
of wine.
Beer spoilage can be caused by some lactic acid bacteria and yeasts. Growth of Pediococcus spp.
causes an increase in acidity and cloudiness. Some Lactobacillus spp. can also multiply and cause
turbidity. Acetobacter and Gluconobacter, in the presence of air, can produce cloudiness and sliminess as well as make the beer sour. Wild yeasts (yeasts other than those used in fermentation) can
grow in beer, causing off-flavor. 14
Canned Foods
Canned foods are heat treated to kill microorganisms present, and the extent of heat treatment
is predominantly dependent on the pH of a food (Chapter 4). High-pH (pH 4.6 and above; also
called low-acid) foods are heated to destroy most heat-resistant spores of the pathogenic bacteria
Clo. botulinum to ensure that a product is free of any pathogen. 1,15 However, spores of some spoilage bacteria, which have greater heat resistance than do spores of Clo. botulinum, can survive.
surface and produce undesirable color and flavor defects in the products. Anaerobic packaging
greatly reduces this problem.
Fermented Vegetable and Fruit Products
Many types of vegetables are fermented, among which cucumber pickles and sauerkraut are produced in large volumes. In salt stock pickles containing approximately 15% salt, yeasts and halophilic bacteria can grow, especially if the acidity is not sufficient. Dill pickles with low salt (<5%)
can have a bloating defect from CO 2 production by yeasts, heterofermentative lactic acid bacteria,
and coliforms, especially if the desirable bacteria associated with fermentation do not grow properly. Candida, Torulopsis, and Saccharomyces spp. are often the causative yeasts. Sweet and sour
pickles preserved with sugar and vinegar can be spoiled from the growth of yeasts and lactic acid
bacteria, especially when the acid level is not sufficient. Sauerkraut can be spoiled from the growth
of yeasts and molds if the air is not excluded during fermentation of cabbage (see Chapter 15).
Failure of lactic acid bacteria to grow rapidly and in proper sequence can lead to low acid production. Under this condition, coliforms and other Gram-negative bacteria can multiply to produce
undesirable flavor, texture, and color defects. Olives are fermented for a long time and are susceptible to many types of spoilage. The most common problem is gassiness (bloating) resulting from
CO 2 production by heterofermentative lactic acid bacteria, coliforms, and yeasts. Softening of
texture can be caused by pectinases of yeasts (Rhodotorula spp.).
Fermented Beverages
Wines can support the growth of film yeasts and acetic acid bacteria (Acetobacter and Gluconobacter)
under aerobic conditions. Film yeasts oxidize alcohol and organic acids and form a surface pellicle,
whereas acetic acid bacteria oxidize alcohol to acetic acid and CO 2 . Under anaerobic conditions,
several lactic acid bacteria (e.g., Lactobacillus, Leuconostoc, and Pediococcus spp.) can grow in wine.
Some heterofermentative Lactobacillus spp. can ferment glucose and fructose and increase the
acidity of wine, producing a defect called tourne spoilage (by Lab. brevis, Lab. buchneri). They
can also produce cloudiness and a mousy odor. Some Leuconostoc spp. can produce sliminess and
cloudiness. Oenococcus oenos can convert malic acid to lactic acid and CO 2 and reduce the acidity
of wine. Sometimes, this malolactic fermentation is used advantageously to reduce the sourness
of wine.
Beer spoilage can be caused by some lactic acid bacteria and yeasts. Growth of Pediococcus spp.
causes an increase in acidity and cloudiness. Some Lactobacillus spp. can also multiply and cause
turbidity. Acetobacter and Gluconobacter, in the presence of air, can produce cloudiness and sliminess as well as make the beer sour. Wild yeasts (yeasts other than those used in fermentation) can
grow in beer, causing off-flavor. 14
Canned Foods
Canned foods are heat treated to kill microorganisms present, and the extent of heat treatment
is predominantly dependent on the pH of a food (Chapter 4). High-pH (pH 4.6 and above; also
called low-acid) foods are heated to destroy most heat-resistant spores of the pathogenic bacteria
Clo. botulinum to ensure that a product is free of any pathogen. 1,15 However, spores of some spoilage bacteria, which have greater heat resistance than do spores of Clo. botulinum, can survive.