Microbiological Profile Of Harvested Fruits And Vegetables

The consumption of fresh fruits and vegetables is increasing as consumers
strive to eat healthy diets. Global trade in fruits and vegetables and changing
horticultural practices have enabled this year-round abundance to be possible,
as well as adding new varieties of fresh produce to the market. During the last
few decades pre-prepared minimally processed fruits and vegetables have
become popular among the consumers.

Microbiological Profile Of Harvested Fruits And Vegetables

These products include pre-washed
pre-cut salads items, grated vegetables, prepared fruit salads, or fruit
combinations. Most of these products are generally eaten raw without further
processing. Some products are packed in modified atmospheres to provide
extension of shelf life both in relation to the potential acceptable quality and
safety of the product. 

Since minimum processing is required for fresh and fresh-cut fruits and
vegetables, which omits any effective microbial elimination step, results in
food products that naturally would carry microorganisms, some of which may
be potentially hazardous to human health.

Sources of Microorganisms on Fresh Fruits and Vegetables

Fruits and vegetables can become contaminated whilst growing in fields, or
during harvest, handling, processing, distribution and use. However, there are
certain factors, which contribute to the microbiological contamination of these
products with pathogens. Table 13.1 lists the sources of pathogenic
microorganisms on fresh produce and conditions that influence their survival
and growth.
Contamination can arise as a consequence of treating soil with organic
fertilizers such as manure and sewage sludge and from irrigation water.
Manure, bio-solids and irrigation water should be of a quality that does not
introduce pathogens to the treated commodity. 
The potential of organic
farming to contaminate fruits and vegetables with pathogens has to be
investigated. Harvesting at the appropriate time and storing the harvested
products under controlled conditions will help to retard growth of post-harvest
spoilage and pathogenic microorganisms. Humid and warm storage conditions
encourage the growth of microbial contaminants. 
The use of additional postharvest procedures could reduce the contamination level of fruits and
vegetables. Washing with water of potable quality can reduce the microbial
load. Although a wide range of different agents are available for disinfecting/
sanitizing fresh produce their efficacy is variable and none is able to ensure
elimination of pathogens. 
Fruits and vegetables carry a natural non-pathogenic
epiphytic micro flora. During growth, harvest, transportation and further
processing and handling the produce can, however, be contaminated with
pathogens from human or animal sources. 
The microbial composition of the
different forms of organic fertilizer will vary depending on its origin and
further treatment. The quality of the water used for irrigation and as a carrier
for plant protection products, fertilizers and frost protection products has to be
related to the potential risk it can cause at a later stage. 
Technologies for
irrigation are important for the control of spreading microbiological hazards.
The use of drip irrigation instead of flooding or spray irrigation should reduce
waterborne contamination and aerosols. However, heavy rains and wind may
provide other opportunities for the transfer of microorganisms from soil to
plant surfaces.

Sources of pathogenic microorganisms on fresh produce and
conditions that influence their survival and growth

Sources of pathogenic microorganisms on fresh produce and conditions

Factors affecting Type and Number of Microorganism on Fresh
Fruits and Vegetables

Fruits and vegetables normally carry a non-pathogenic epiphytic micro flora.
The majority of bacteria found on the surface of plants are usually Gramnegative and belong either to the Pseudomonas group or to the

Many of these organisms are normally non-pathogenic
for humans. The numbers of bacteria present will vary depending on seasonal
and climatic variation and may range from 104 to 108
per gram. The inner
tissues of fruits and vegetables are usually regarded as sterile. 
bacteria can be present in low numbers as a result of the uptake of water
through certain irrigation or washing procedures. If these waters are
contaminated with human pathogens these may also be introduced. The
survival or growth of contaminating microorganisms is affected by intrinsic,
extrinsic and processing factors. 
Factors of importance are nutrient
composition, pH, presence of scales and fibers, redox potential, temperature
and gaseous atmosphere. Mechanical shredding, cutting and slicing of the
produce open the plant surfaces to microbial attack. About two thirds of the
spoilage of fruits and vegetables is caused by molds. 
Members of the genera
Penicillium, Aspergillus, Sclerotinia, Botrytis and Rhizopus are commonly involved in this process. The spoilage is usually associated with cellulolytic or
pectinolytic activity, which causes softening of tissues, and weakening of
plant structures. These structures are important barriers to prevent growth in
the products by contaminating microbes.

Human Pathogens Associated with Fresh Fruits and Vegetables

However, risk profile surveys on the microbiological contamination of fruits
and vegetables eaten raw demonstrates, potential for a wide range of these
products to become contaminated with microorganisms, including human
The range of microorganisms associated with outbreaks linked to
fresh produce encompasses bacteria, viruses and parasites. Most of the
reported outbreaks have been associated with bacterial contamination,
particularly members of the Enterobacteriaceae. Of these, Salmonella and
Escherichia coli O157 are of particular concern. 
Outbreaks of illness caused
by bacteria, viruses and parasites have been linked epidemiologically to the
consumption of a wide range of vegetables and, to a lesser extent fruits.
Surveillance of vegetables has indicated that these foods can be contaminated
with various bacterial pathogens, including Salmonella, Shigella, E. coli
O157:H7, Listeria monocytogenes and Campylobacter. Table 13.2 shows the
characteristics of some microbial pathogens that have been linked to outbreaks
of fresh fruits and vegetable associated illness.

Characteristics of some microbial pathogens that have been
linked to outbreaks of produce associated illness

Characteristics of some microbial pathogens that have been linked to outbreaks of produce associated illness
Characteristics of some microbial pathogens that have been linked to outbreaks of produce associated illness
However, multiplication of the pathogen is also essential for causing any
damage. Some microorganisms cause illness only when ingested in high
numbers (for example, Clostridium perfringens), while in other cases, the
infectious dose is thought to be dependent upon the susceptibility of the
individual (most infectious agents). 
Illness due to Staphylococcus aureus,
Bacillus cereus, or Clostridium botulinum is a result of the production of
toxins in the food, and it is the toxins that are responsible (sometimes in the
absence of viable cells) for symptoms of the disease. These toxins are only
produced by multiplying cells. This requires favourable growth conditions. 

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