Microbial Ecology of Spoilage 383
severe tissue breakdown, causing mushy areas; this spoilage is termed “rot.” The
names given to the different rots indicate the appearance of the food when it is
spoiled [1]. The most common forms of bacterial and fungal spoilage are listed in
Table 12.1 and Table 12.2.
An important cause of spoilage is Penicillium, many species of which are able
to attack fruits; perhaps as much as 30% of all fruit decay can be attributed to this
genus. Many fruits and vegetables, such as tomatoes, cucumbers, potatoes, and beets,
are susceptible. Penicillium has a velvety colony that has blue-green centers with
pale to bright yellow or yellow exudate. It has a fruity odor and has been isolated
from decaying cabbage and barley plants, soils, stored seeds of cereals, grapes, nuts,
dried fruits, and fruit juices. Another important disease is Rhizopus soft rot, which
affects a wide range of fruits and vegetables, particularly during transit under poor
refrigeration. Harvested strawberries and potatoes are often attacked and spoiled as
indicated by soft, mushy areas with grayish mycelium evident in the affected areas [58].
Fusarium is a common soil fungus that sporulates in warm, wet weather and is
widely found on grasses and other plants. It is found regularly on banana roots and
other fruits and vegetables such as tomatoes and watermelons.
TABLE 12.1
Microbial Spoilage of Different Vegetables
Spoilage Type Microorganisms Involved Vegetables Affected
Alternaria leaf spot Alternaria brassicae and
Alternaria oleracea
All cruciferous leafy vegetablesBacterial soft rot Erwinia carotovora and others Celery, all cruciferous leafy vegetables,beets
and chards, lettuce, spinach, etc.
Bacterial leaf spot Pseudomonas maculicola Broccoli and cauliflower
Black rot Xanthomonas campestris All cruciferous leafy vegetables
Bacterial zonate spot Pseudomonas cichorii Cabbage primarily
Brown spot Cephalosporium apii Celery
Brown rot Alternaria brassicae Cauliflower (curd)
Big vein Olipidium brassicae Lettuce
Cercospora leaf spot Cercospora beticola Beets and chards
Downy mildew Peronospora parasitica Cabbage and cauliflower
Downy mildew Bremia lactucae and
Peronospora effusa
Lettuce/spinachGray mold rot Botrytis cinerea Celery, broccoli, brussels sprouts, cabbage
and cauliflower, artichokes, and lettuce, etc.
Late blight Septoria apiicola Celery
Rhizoctonia head rot Rhizoctonia solani Cabbage mainly
Rhizopus soft rot Rhizopus stolonifer Brussels sprouts, cabbage, and cauliflower
Ring spot Mycosphaerella brassicicola Mainly cauliflower; occasionally brussels
sprouts, cabbage, and kale
Watery soft rot Various Sclerotinia spp. Celery and lettuce
Source:From Rubatzky, V.E. and Yamaguchi, M., World Vegetables: Principles, Production and Nutritive
Values, 2nd ed., Aspen Publishing, Gaithersburg, MD, 1999.