Fundamental Food Microbiology, Third Edition - Fuad Fathir

SPOILAGE OF SPECIFIC FOOD GROUPS 279
vegetables. The presence of air, high humidity, and higher temperature during storage
increases the chances of spoilage. The most common spoilage is caused by different
types of molds, some of those from genera Penicillium, Phytopthora, Alternaria,
Botrytis, and Aspergillus. Among the bacterial genera, species from Pseudomonas,
Erwinia, Bacillus, and Clostridium are important. 1–3
Microbial vegetable spoilage is generally described by a common term rot, along
with the changes in the appearance, such as black rot, gray rot, pink rot, soft rot,
stem-end rot. In addition to changes in color, microbial rot causes off-odor and loss
of texture. This is more apparent in ready-to-eat cut salads, and sliced vegetables
and fruits that are refrigerated for a long time (3 to 4 weeks) and can be temperature
abused.
Refrigeration, vacuum or modified atmosphere packaging, freezing, drying, heat
treatment, and chemical preservatives are used to reduce microbial spoilage of
vegetables. Spoilage of canned vegetables, vegetable juices, and fermented vegetables
are discussed later in this chapter.
B. Fruits
Fresh fruits are high in carbohydrates (generally 10% or more), very low in proteins
(£1.0%), and have a pH 4.5 or below. Thus, microbial spoilage of fruits and fruit
products is confined to molds, yeasts, and aciduric bacteria (lactic acid bacteria,
Acetobacter, Gluconobactor). Like fresh vegetables, fresh fruits are susceptible to
rot by different types of molds from genera Penicillium, Aspergillus, Alternaria,
Botrytis, Rhizopus, and others. According to the changes in appearance, the mold
spoilage is designated as black rot, gray rot, soft rot, brown rot, or others. Yeasts
from genera Saccharomyces, Candida, Torulopsis, and Hansenula are associated
with fermentation of some fruits, such as apples, strawberries, citrus fruits, and dates.
Bacterial spoilage associated with souring of berries and figs has been attributed to
the growth of lactic acid and acetic acid bacteria. 1–3
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.
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VII. 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 to 4.0). The carbohydrate
(sucrose, glucose, and fructose) content ranges from 5 to 15% in juices and drinks,
but 40 to 60% in concentrates and preserves. High sugar content reduces the A w of
these products, which in the concentrates and preserves can be ca. 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. In carbonated