1. Microbiology of Fruit and Vegetables
A.Poshadri
Asst.Professor – Food Technology

2. Introduction
• Fruits and vegetables can become contaminated
with pathogenic microorganisms during
harvesting through water, faecal material soil
and human handling, harvesting equipment,
transport containers, wild and domestic animals,
air transport vehicles ice etc
air, transport vehicles, ice etc.
• During transportation to market or the
processing plant, mechanical damage may
increase susceptibility to decay and growth of
microorganisms may take place.
• Pre-cooling of the product and refrigeration
during transportation will slow such growth.

3. • Washing with detergent or germicidal solutions will reduce
numbers of microorganisms on the foods.
• Sorting spoiled fruits or vegetables or trimming spoiled parts
removes microorganisms, but additional handling may result in
mechanical damage and therefore greater susceptibility to decay.
• Adequate washing at the plant causes a reduction in numbers of
microorganisms on the food, as do peeling by steam, hot water,
or lye and blanching (heating to inactivate enzymes, etc.,)
• Sweating of products during handling increases numbers.
• Processes such as trimming, mechanical abrasion or peeling,
cutting, pitting or coring, and various methods of disintegration
may add contaminants from the equipment involved

4. • Hot-water blanching, although it reduces total numbers of organisms on
the food, may cause the buildup of spores of thermophilic bacteria, causing
the spoilage of canned foods. e.g., flat sour spores in peas.
• Inclusion of decayed parts of fruits increases the numbers of
microorganisms in fruit juices.
• Numbers in orange juice, for example, and numbers of coliforms are
increased greatly by the inclusion of fruits with soft rots.
• Heating of grapes before extraction reduces numbers of organisms in the
expressed juice, but pressing introduces contamination.

5. • The kinds of microorganisms from
equipment will depend on the product
being processed, for that product will
constitute the culture medium for the
organisms
• The numbers of such organisms on
poorly cleaned and sanitized equipment
may be high at the start of a day’s run
and decrease as the day progresses, but
the reverse usually is true.
• A layoff during the run permits a
renewed increase in numbers.

6. Preservation
• If the surfaces are moist or the outer
surface has been damaged, growth of
some microorganisms may take place
between harvesting and processing or
consumption of the vegetables.
Adequate control of and
• Adequate control of temperature and
humidity will reduce such growth
• Chlorinated water sometimes is used
for washing, and detergents may be
added to facilitate the removal of dirt
and microorganisms

7. • Asepsis: Avoid cross contamination during
harvesting, transport, processing storage
and consumption.
• Use clean and sanitized Boxes, lugs,
baskets, and other containers during all
stages of handling
Preservation
stages of handling
• Contact of vegetables undergoing spoilage
with healthy vegetables will add
contamination and may lead to losses.
• Contamination from equipment at the
processing plant can be reduced by
adequate cleaning and sanitizing

8. Use of heat: Vegetables to be dried or
frozen, and some to be canned, are
scalded or blanched to inactivate their
enzymes.
• The numbers of microorganisms are
reduced appreciably, perhaps by
Preservation
reduced appreciably, perhaps by
1,000- to 10,000- fold by using heat
processing
• Sterilization, pasteurization , Canning
and Aseptic packaging or processing
techniques use heat as medium to
reduce or eliminate microbial load.

9. Use of Low temperature:
Chilling:Most vegetables to be preserved without special processing are cooled
promptly and kept at chilling temperatures.
• The chilling is accomplished by use of cold water, ice, or mechanical
refrigeration or by vacuum cooling (moistening plus evacuation), as used for
lettuce.
Preservation
• In many cases pre-cooling, i.e., cooling before normal cold storage, is done
immediately after harvesting by use of a cold water spray, a practice referred to
as hydrocooling.
• Ordinary potatoes turn sweet at temperatures below 2.2 to 4.4°C and are
stored at higher temperatures if they are to be used for potato chips.
• Sweet potatoes and onions are subjected to special curing treatments before
storage.

10. Freezing: The freezing process reduces the number of organisms by a percentage
that varies with the kinds and numbers originally present, but on the average
about half of them are killed
• The kind of bacteria most likely to grow on thawing will depend on the
temperature and the elapsed time.
• Micrococcus* are predominant on thawing vegetables such as sweet corn and
Use of Low temperature:
• Micrococcus* are predominant on thawing vegetables such as sweet corn and
peas when the temperature of thawing is fairly low.
• Achromobacter*, Clostridium botulinum and Enterobacter spp. also are
commonly found in thawed vegetables.
• At higher temperatures, species of Flavobacterium also may multiply
• Bacterial counts in frozen vegetables may range from a few to 102 per gram

12. Drying: Many vegetables can be dried by a process called 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.
Preservation
• This results in an additional loss of water, but more important, a porous
network of capillaries is formed in the product. The increased porosity
simplifies further drying and imparts good reconstituting ability.
• Dried vegetables and vegetable products are used in dried soups,
and dried spices and condiments are used as flavoring materials

13. • Drying by heat destroys yeasts and most bacteria, but spores of bacteria
and molds usually survive, as do the more heat-resistant vegetative
cells.
• Most vegetables are less acid than fruits, and consequently the killing
effect of the heat is less.
• When dried vegetables are sulfured (2000 ppm) to preserve a light
color, their microbial content is reduced.
• If the vegetables are dried adequately and stored properly, there will be
no growth of microorganisms in them.
• The spores of bacteria and molds, some of the micrococci*, and
microbacteria are resistant to desiccation and will survive better than
other microorganisms

15. Use of Preservatives:
• Rutabagas and turnips sometimes are paraffined to lengthen their
keeping time.
• Zinc carbonate has been reported to eliminate most mold growth on
Preservation
lettuce, beets, and spinach.
• Biphenyl vapors will control Fusarium on potatoes.
• A controlled atmosphere of carbon dioxide or ozone about chilled
vegetables has been tried experimentally but has had little practical use.

16. Added Preservative: Sodium chloride is the only added chemical
preservative in common use.
The amount added to vegetables may vary from the 2.25 to 2.5 percent
in making sauerkraut up to saturation for cauliflower.
The lower concentrations of salt permit an acid fermentation by bacteria
to take place; as the percentage of salt is increased, the rate of acid
production becomes slower until a level of salt is reached that will permit
production becomes slower until a level of salt is reached that will permit
no growth or production of acid.
Vegetables that are high in protein, such as green peas and lima beans,
as well as some that soften readily, such as onions and cauliflower, are
preserved by the addition of enough salt to prevent any fermentation:
from 70 to 80° salometer (18.6 to 21.2 percent salt) up to saturation
(26.5 percent salt, or 100° salometer).

17. Developed Preservatives: At room temperature an acid fermentation is
normal for shredded, chopped, or crushed vegetables containing sugar,
but instead of a clean, acid flavor from the action of lactic acid bacteria,
undesirable flavors and changes in body may result from growth of
coliform bacteria, bacilli, anaerobes, proteolytic bacteria, and others.
• The salt also serves to draw the juice from the vegetables and bring
juice vegetables bring
about better distribution of the lactic acid bacteria.
• The amount of sugar in the vegetable affects the acidity that can be
produced, while the amount of salt and the temperature determine the
rate of acid production and the kinds of bacteria involved in it.

18. On the basis of pH:4.5 is the dividing
line between foods
-the acid foods, such as tomatoes,
pears, and pineapples, or
-the high-acid foods, such as berries.
PRESERVATION OF FRUITS AND FRUIT PRODUCTS
In general, the more acid the fruit, the
less heat required for its preservation
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

19. Use of Low Temperatures: Each fruit has its own optimal temperature and
relative humidity for chilling storage; even varieties of the same fruit may differ in
their requirements
Fruits have been treated with various chemicals before or during storage to aid in
their preservation. Thus hypochlorites, sodium bicarbonate, borax, propionates,
biphenyl, phenylphenols sulfur dioxide, thiourea thiabendazole
PRESERVATION OF FRUITS AND FRUIT PRODUCTS
biphenyl, o-phenylphenols, sulfur dioxide, thiourea, thiabendazole,
dibromotetrachloroethane, and other chemicals have been recommended.
Fruit also has been enclosed in wrappers treated with chemicals, e.g., sulfite paper
on grapes, iodine aper on grapes and tomatoes, or borax paper on oranges. Waxed
wraps, paraffin oil, paraffin, waxes, and mineral oil have been applied for
mechanical protection

20. • Controlled-atmosphere (CA) storage implies the altering of various gases from
normal atmospheric concentration. Usually this is done by increasing the CO2
concentration and decreasing the O2 concentration.
• Modified atmosphere (MA )storage is usually used to describe CA conditions
which are not accurately maintained or conditions where the air is initially
replaced with gas but no further measures are taken to keep the gas
atmosphere constant.
• Under certain circumstances only one gas is used, e.g., packaging a product in
100 percent N2; this type of storage would more precisely be referred to as
nitrogen gas storage

22. Conditions of Controlled-atmosphere Storage for Several Fruits and
Vegetables
Ozone in concentrations 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.
Ethylene in the atmosphere is used to hasten ripening or produce a desired color
change

23. • Freezing: Some fruits are frozen in large drums (up to 50 lb); it would be mandatory
to cool the fruit before filling the container to ensure that the product is frozen
quickly.
• Yeasts (Saccharomyces, Cryptococcus) and molds (Aspergillus, Penicillium, Mucor,
Rhizopus, Botrytis, Fusarium, Alternaria, etc.) have been reported to be the
predominant organisms in frozen fruits, although small numbers of soil organisms,
e.g., species of Bacillus, Pseudomonas, Achromobacter*, etc., survive freezing.
• Yeasts are most likely to grow during slow thawing
• Numbers of viable microorganisms in frozen fruits are considerably lower than in
frozen vegetables.

24. • The numbers of microorganisms in frozen fruit juices depend on the condition of
the fruit, the washing process, the method of filtration, and the opportunities
for contamination and growth before freezing.
• The freezing process markedly reduces numbers, but added sugar or increased
concentration of the juice has a protective effect against killing.
• The decrease in numbers of organisms during storage in the frozen condition is
slow but is faster than in most neutral foods.
• Drying: Alkali treatment, sulfuring, blanching, and pasteurization or drying
reduce numbers of microorganisms

25. Use of Preservatives: Among substances that have been applied to the outer
surfaces of fruit are waxes, hypochlorites, biphenyl, and alkaline sodium o-
phenylphenate.
Wrappers for fruits have been impregnated with a variety of chemicals including
iodine, sulfite, biphenyl, o-phenylphenol plus hexamine, and others. As a gas or
fog about the fruit, carbon dioxide, ozone, and ethylene plus chlorinated
hydrocarbons have been tried.
Sulfur dioxide and sodium benzoate are preservatives that have been added
directly to fruits or fruit products.

26. Deterioration of raw vegetables and fruits mostly due to
– Physical factors,
– action of their own enzymes,
– microbial action, or
– combinations of these agencies.
SPOILAGE
• Mechanical damage resulting from action of animals, birds, or insects or
from bruising, wounding, bursting, cutting, freezing, desiccation, or
other mishandling may predispose toward increased enzymatic action or
the entrance and growth of microorganisms.
• Improper environmental conditions during harvesting, transit, storage,
and marketing may favor spoilage.

27. Microbial spoilage may be due to
(1) plant pathogens acting on the stems, leaves, flowers, or roots of
the plant, on the fruits or other special parts used as foods, e.g.,
roots or tubers, or on several of these locations, or
(2) Saprophytic organisms which may be secondary invaders after
General Types of Microbial Spoilage
(2) Saprophytic organisms, which may be secondary invaders after
action of a plant pathogen or may enter a healthy fruit or
vegetable, as in the case of various “rots,” or grow on its surface,
as when bacteria multiply on moist, piled vegetables.
• At times a saprophyte may succeed a pathogen or a succession of
saprophytes may be involved in the spoilage

28. Bacterial soft rot: -
• caused by Erwinia carotovora
and related species, which are
fermenters of pectins.
• Pseudomonas marginalis and
Clostridium and Bacillus spp
SPOILAGE
Clostridium and Bacillus spp.
have also been isolated from
these rots.
• It results in a water-soaked
appearance, a soft, mushy
consistency, and often a bad
odor.

29. • Gray mold rot: caused by
species of Botrytis, e.g.,
B. cinerea, a name derived
from the gray mycelium of
SPOILAGE
from the gray mycelium of
the mold.
• It is favored by high
humidity and a warm
temperature.

30. • Rhizopus soft rot: caused by
species of Rhizopus, e.g., R.
stolonifer.
• A rot results that often is soft and
SPOILAGE
A rot results that often
mushy.
• The cottony growth of the mold
with small, black dots of sporangia
often covers masses of the foods.

31. • Anthracnose: usually caused
by Colletotrichum
lindemuthianum, C. coccodes,
and other species.
SPOILAGE
• The defect is a spotting of
leaves and fruit or seedpods

32. • Alternaria rot: caused by Alternaria tenuis and other species. Areas
become greenish-brown early in the growth of the mold and later turn
to brown or black spots.
SPOILAGE
• Blue mold rot: caused by species of Penicillium digitatum and other
species. The bluishgreen color that gives the rot its name results from
the masses of spores of the mold.

33. Downy mildew: caused by species of Phytophthora, Bremia, and other
genera.
• The molds grow in white, woolly masses.
SPOILAGE
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

34. • Black mold rot caused by
Aspergillus niger.
• The rot gets its name from the
dark-brown to black masses
SPOILAGE
of spores of the mold, termed
“smut” by the layperson

35. • Black rot: caused by species of
Alternaria but sometimes of
Ceratostomella, Physalospora, and
other genera.
SPOILAGE
Pink mold rot: caused by pink-
spored Trichothecium roseum

36. • Fusarium rots: a variety of types of
rots caused by species of Fusarium
SPOILAGE
Green mold rot: caused usually by
species of Cladosporium but
sometimes by other green spored
molds, e.g., Trichoderma

37. • Brown rot: caused chiefly by Sclerotinia (Monilinia fructicola)
species..
SPOILAGE
• Sliminess or souring: caused by saprophytic bacteria in piled.
wet, heating vegetables

38. The Chief Market Diseases of Several Vegetables and Fruits

41. Spoilage of fruit and vegetable juices
Molds can grow on the surface of acidic fruit juices if juices are exposed to air.
The lactic acid fermentation of sugars, mostly by heterofermentative lactic acid
bacteria such as Lactobacillus pastorianus, Lactobacillus brevis and Leuconostoc
mesenteroides.
Acetic acid fermentation- by lactic acid bacteria. E.x. Lactobacillus psatorianus.
Slime production- by Leuconostoc mesenteroides, Lactobacillus brevis, and
Lactobacillus plantarum in apple juice and by L. plantarum and Streptocooci in
grape juice.

42. • Vegetable juices contain sugars but are less acid than fruit juices, having
pH values in the range of 5.0 to 5.8 for the most part.
• Concentrates of fruit and vegetable juices, because of their increased
acidity and sugar concentration, favor the growth of yeasts and of acid-
and sugar-tolerant Leuconostoc and Lactobacillus species