2. Introduction:
We discuss about characteristics of spoilage
microorganisms associated with fruit and vegetable
categories including spoilage mechanisms, spoilage
defects, prevention and control of spoilage.
3. Unusual Characteristics of Spoilage Microorganisms in fruits
and vegetable products:
Microbial spoilage in fruits and vegetables varies not only with
the kind of fruit or vegetables but also to some extent with the
variety. Microbial spoilage may due to
(1) plant pathogens acting on stems, leaves, flowers, or root of
the plant, on the fruit or other special parts used as foods
(2) saprophytic organisms, which may be secondary invaders
after the action of plant pathogen or may enter a healthy fruit or
vegetable
4. Major causes of fruit deterioration include
the following:
Spoilage organisms:
Yeasts: target fruits and vegetables due to their low pH
Moulds: can grow even at very low water activity
Bacteria: most bacteria have limited pH, prolytic bacteria can grow even in
media with high pH
Water activity: lower water activity inhibits microbial growth
pH: most microorganisms have limited pH range
Nutrient contents: growth rate faster is nutrients abundant
Temperature: lower temperature
5. The most commonly occurring types of microbial spoilage
are as follows in fruits and vegetables:
Bacterial soft rot, caused by Erwinia crtatowa and related species, which
are fermenters of pectins, Pseudomonas marginalis, Clostridium and Bacillus
spp. Have also been associated with these rots. It results water-soaked
appearance, a soft, mushy consistency, and often a bad odor.
Gray mold rot: caused by species of Botrytis, eg: B.cinerea, which is
favored by high humidity and warm temperature
6. Rhizopus soft rot: caused by species Rhizopus, eg R.stolonifer. A
rot results that often is soften and mushy. The cottony growth of
the mold with small, black dots of sporangia often covers masses
of the foods.
Anthracnose: usually caused by Colletotrichum
lindemuthianum, C. coccodes and other species. The defect is a
spotting of leaves and fruit or seedpods.
7. Downy mildew:caused by species of Phytophthora, Bremia, and
other genera. The molds grow in white, woolly masses.
Watery soft rot: caused chiefly by Sclerotinia sclerotiorum, is
found mostly in vegetables.
Stem-end rots:caused by species of molds of several genera,
e.g., Diplodia, Alternaria, Phomopsis, Fusarium, and others,
involve the stem ends of fruits.
8. Black mold rot: caused by Aspergillus niger. The rot gets its
name from the dark-brown to black masses of spores of the mold,
termed "smut“
Sliminess or souring: caused by saprophytic bacteria in piled,
wet, heating vegetables.ure retards microbial growth
9.
10.
11. PRESERVATION OF VEGETABLES AND VEGETABLE
PRODUCTS;
Adequate control of temperature and humidity will reduce the growth of
micro organisms
Boxes, lugs, baskets and other containers should be practically free of the
growth of micro organisms, and some will need cleaning and sanitation
between uses.
Contamination from equipment at the time of processing plant can be
reduced by adequate cleaning and sanitizing. Preservation is done by various
methods
Removal of micro organisms through washing of vegetables which removes
most of the contamination on the surface but leaves much of the natural
microbial flora. Unless the washed water is of good bacteriological quality, it
may add organisms and subsequently growth may take place at the moist
surface.
Use of heat: Vegetables to be dried or frozen, and some to be canned, are
scalded or blanched to inactivate their enzymes.
12. Use of low temperature
A few kinds of vegetables that are relatively stable, such as root crops, potatoes,
cabbage, and celery, can be preserved for a limited time by common or cellular
storage.
Chilling:
Most vegetables to be preserved without special processing are cooled promptly and
kept at chilling temperature. The chilling is accomplished by use of cold water, ice, or
mechanical refrigerator or by vacuum cooling. In many cases precooling, i.e. cooling
before normal cold storage is done immediately after harvesting by use of a cold water
spray, a practice referred to as hydro cooling.
• Freezing:
The washing of vegetables reduces the numbers of some organisms and add some
organisms, and scalding or blanching( 86 to 98 C) brings about a great reduction in
numbers, as much as 90 to 99% in some instances. During storage in frozen conditions
there is a steady decrease in number of organisms, but there are at least some survivors
of most kind of organisms after the usual storage periods
13. Drying:
Dried vegetables and vegetable products are used in dried soups,
and dried species and condiments are used as flavoring material.
Many vegetables can be dried by the process of explosive puffing.
Usually small pieces of the diced, partially dehydrated vegetables
are placed in a closed rotating chamber. Heat is applied, and the
chamber is pressurized to a predetermined level; then the pressure
is released instantaneously
14. Use of preservatives:
Rutabagas and turnips some times are paraffined to lengthen their
keeping time. Zinc carbonate has been reported to eliminate most
mold growth on lettuce, beets, spinach. Biphenyl vapors will
control Fusarium on potatoes. Sodium chloride is the only added
chemical preservatives in common use. There are added
preservatives and developed preservatives which are used
15. PRESERVATION OF FRUITS AND FRUIT
PRODUCTS:
Fruits may be subjected to contamination between harvesting and
processing from containers and from spoiling fruits, and care
should be taken to avoid such contamination as much as possible.
Before harvest, fruits are usually exposed to insecticides and
fungicides and may have their flora altered by such treatments
16. Removal of micro organisms
Through washing of fruits serves to remove not only dirt
and hence causal contaminating micro organisms but also
poisonous sprays
Washing may be with water, detergent solutions, or even
bactericidal solutions such as chlorinated water
T rimming also removes micro organisms.
17. Use of heat
Fruits seldom are blanched before other processing
because blanching causes excessive physical damage.
A steam pressure sterilizer is not required for most fruits,
since heating at about 100 C is sufficient and can be
accomplished by flowing steam or boiling water.
• In general, the more acidic the fruit, the less heat
required for its preservation.
18. Use of low temperature:
Chilling:
Each fruit has its own optimum temperature and relative humidity for chilling storage; even
varieties of the same fruit may differ in their requirement.
Controlled atmosphere storage implies the altering of various gases from normal
atmospheric concentrations. Usually this is done by increasing the CO2 concentration and
decreasing the O2 concentration
Ozone in concentration of 2 to 3 ppm in the atmosphere has been reported to double the
storage time of loosely packed small fresh fruits, such as strawberries, raspberries, currants,
and grapes and of delicate varieties of apples.
Freezing: • During preparation of fruits for freezing, undesirable changes may take place,
such as darkening, deterioration in flavor, and spoilage by micro organisms, especially
molds.
19. Use of preservatives:
• Chemicals have been applied to fruits chiefly as a dip or spray or
impregnated in wrappers for fruits.
Among substances that have been applied to the outer surfaces of
fruits are waxes, hypochlorites, biphenyl, and alkaline sodium o-
phenyl phenate.
Wrappers for fruits have been impregnated with variety of chemicals
including iodine, sulfite, biphenyl, o-phenyl phenol plus hexamine, and
others.
Green olives are the only fruits which are preserved on a commercial
scale with assistance from an acid fermentation.
Locally, other fermented fruits sometimes are prepared, such as
fermented green tomatoes and Rumanian preserved apples.
