264 ◾ Fundamental Food Microbiology
To reduce spoilage, fruits and fruit products are preserved by refrigeration, freezing, drying,
reducing A W , and heat treatment. Spoilage of fruit juices, jams, and wine is discussed later.
Soft Drinks, Fruit Juices and Preserves, and Vegetable Juices
Carbonated and noncarbonated soft drinks, fruit juices, and preserved and concentrated fruit
juices and drinks are low-pH products (pH 2.5–4.0). The carbohydrate (sucrose, glucose, and
fructose) content ranges from 5% to 15% in juices and drinks but is 40%–60% in concentrates
and preserves. High sugar content reduces the A W of these products, which, in the concentrates
and preserves, can be approximately 0.9. Carbonated beverages also have low O-R potential.
Among the microorganisms that can be present in these products, only aciduric molds, yeasts,
and bacteria (Lactobacillus, Leuconostoc, and Acetobacter) are able to cause spoilage if appropriate preservation methods are not used. 11 In carbonated beverages, some yeast species from genera
Torulopsis, Candida, Pichia, Hansenula, and Saccharomyces can grow and make the products turbid.
Some Lactobacillus and Leuconostoc species can also grow to cause cloudiness, and Leuconostoc can
cause ropiness (resulting from production of dextrans) of the products. Noncarbonated beverages
can be similarly spoiled by yeasts, Lactobacillus, and Leuconostoc spp. In addition, if there is enough
dissolved oxygen, molds (Penicillium, Aspergillus, Mucor, and Fusarium) and Acetobacter can grow;
the latter produces acetic acid to give a vinegar-like flavor. Fruit juices are susceptible to spoilage by
molds, yeasts, Lactobacillus, Leuconostoc, and Acetobacter spp. However, a particular type of juice
may be susceptible to spoilage by one or another type of microorganism. Molds and Acetobacter can
grow if enough dissolved oxygen is available. Yeasts can cause both oxidation (producing CO 2 and
H 2 O) and fermentation (producing alcohol and CO 2 ) of the products. Acetobacter can use alcohol to
produce acetic acid. Heterofermentative Lab. fermentum and Leu. mesenteroides can ferment carbohydrates to lactate, ethanol, acetate, CO 2 , diacetyl, and acetoin. In addition, Leu. mesenteroides and
some strains of Lab. plantarum can produce slime as a result of production of dextran and other exopolysaccharides. In fruit drinks, Lactobacillus and Leuconostoc spp. can also convert citric and malic
acids (additives) to lactic and acetic acids and reduce the sour taste (flat flavor). Because concentrated
fruit drinks and fruit preserves have a low A W (0.9), only osmophilic yeasts can grow; molds also
can grow if oxygen is available. A new group of bacterial species, Alicyclobacillus (e.g., Alicyclobacillus
acidoterrestris), has been recognized recently to cause spoilage of low-pH fruits and vegetable juices.
To prevent growth of these potential spoilage microorganisms, several additional preservation
methods are used for these products, which include heat treatment, freezing, refrigeration, and
addition of specific chemical preservatives.
Tomato juice has a pH of approximately 4.3. It is generally given high heat treatment to kill
vegetative microorganisms. However, bacterial spores can survive. Flat sour spoilage of tomato
juice resulting from germination and growth of Bac. coagulans is documented. Most other vegetable juices have pH values between 5.0 and 5.8, and many have growth factors for lactic acid
bacteria. These products are susceptible to spoilage because of the growth of many types of microorganisms. Effective preservation methods are used to control their growth.
Cereals and their Products
Some of the products susceptible to microbial spoilage include high-moisture cereal grains, germinated or sprouted seeds and grains, refrigerated dough, breads, soft pastas, and pastries. 1
To reduce spoilage, fruits and fruit products are preserved by refrigeration, freezing, drying,
reducing A W , and heat treatment. Spoilage of fruit juices, jams, and wine is discussed later.
Soft Drinks, Fruit Juices and Preserves, and Vegetable Juices
Carbonated and noncarbonated soft drinks, fruit juices, and preserved and concentrated fruit
juices and drinks are low-pH products (pH 2.5–4.0). The carbohydrate (sucrose, glucose, and
fructose) content ranges from 5% to 15% in juices and drinks but is 40%–60% in concentrates
and preserves. High sugar content reduces the A W of these products, which, in the concentrates
and preserves, can be approximately 0.9. Carbonated beverages also have low O-R potential.
Among the microorganisms that can be present in these products, only aciduric molds, yeasts,
and bacteria (Lactobacillus, Leuconostoc, and Acetobacter) are able to cause spoilage if appropriate preservation methods are not used. 11 In carbonated beverages, some yeast species from genera
Torulopsis, Candida, Pichia, Hansenula, and Saccharomyces can grow and make the products turbid.
Some Lactobacillus and Leuconostoc species can also grow to cause cloudiness, and Leuconostoc can
cause ropiness (resulting from production of dextrans) of the products. Noncarbonated beverages
can be similarly spoiled by yeasts, Lactobacillus, and Leuconostoc spp. In addition, if there is enough
dissolved oxygen, molds (Penicillium, Aspergillus, Mucor, and Fusarium) and Acetobacter can grow;
the latter produces acetic acid to give a vinegar-like flavor. Fruit juices are susceptible to spoilage by
molds, yeasts, Lactobacillus, Leuconostoc, and Acetobacter spp. However, a particular type of juice
may be susceptible to spoilage by one or another type of microorganism. Molds and Acetobacter can
grow if enough dissolved oxygen is available. Yeasts can cause both oxidation (producing CO 2 and
H 2 O) and fermentation (producing alcohol and CO 2 ) of the products. Acetobacter can use alcohol to
produce acetic acid. Heterofermentative Lab. fermentum and Leu. mesenteroides can ferment carbohydrates to lactate, ethanol, acetate, CO 2 , diacetyl, and acetoin. In addition, Leu. mesenteroides and
some strains of Lab. plantarum can produce slime as a result of production of dextran and other exopolysaccharides. In fruit drinks, Lactobacillus and Leuconostoc spp. can also convert citric and malic
acids (additives) to lactic and acetic acids and reduce the sour taste (flat flavor). Because concentrated
fruit drinks and fruit preserves have a low A W (0.9), only osmophilic yeasts can grow; molds also
can grow if oxygen is available. A new group of bacterial species, Alicyclobacillus (e.g., Alicyclobacillus
acidoterrestris), has been recognized recently to cause spoilage of low-pH fruits and vegetable juices.
To prevent growth of these potential spoilage microorganisms, several additional preservation
methods are used for these products, which include heat treatment, freezing, refrigeration, and
addition of specific chemical preservatives.
Tomato juice has a pH of approximately 4.3. It is generally given high heat treatment to kill
vegetative microorganisms. However, bacterial spores can survive. Flat sour spoilage of tomato
juice resulting from germination and growth of Bac. coagulans is documented. Most other vegetable juices have pH values between 5.0 and 5.8, and many have growth factors for lactic acid
bacteria. These products are susceptible to spoilage because of the growth of many types of microorganisms. Effective preservation methods are used to control their growth.
Cereals and their Products
Some of the products susceptible to microbial spoilage include high-moisture cereal grains, germinated or sprouted seeds and grains, refrigerated dough, breads, soft pastas, and pastries. 1