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Pre-Storage Treatments
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Introduction
Pre storage treatments are the treatments given
to a commodity (fruits and vegetables in present
context) generally after harvesting to reduce
postharvest losses, enhance storage life and
retain quality. Some of the important pre
storage treatments are Cleaning, Washing,
Sorting, Grading, Waxing, Packing, Pre
cooling, Curing, Desapping, Chemical
treatments, Irradiation, Vapour heat treatment
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1. Cleaning This is a treatment given to remove
adhering dust, dirt, extraneous matter,
pathogenic load etc. from the surface of a
commodity. Cleaning basically sanitizes the
produce and avoid entry of undesirable contents
to enter the packaging and storage line.
Cleaning is a broader term and includes, dusting,
washing etc. Methods of cleaning i. Dry method
(Dusting etc.) ii. Wet method (Washing)
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i. Dusting This method is mainly used to remove
the adhering soil, etc from commodity i.e.
potato, root vegetables, carrot, radish etc.
Dusting helps to shed undesirable load (weight)
of the commodity and thus reduce transportation
cost. It also removes pathogenic microorganisms
present in the soil from the surface of the
vegetables. ii. Washing This method is used
in most fruits and vegetables. Washing is done at
the pack house through automated washing system
fitted with overhead sprayers and smooth rotating
brushes to clean and wash the fruits. Washing
with clean water mixed with a neutral detergent
such as Teapol, Sandovit or Indtron at 0.1 (1 ml
/ litre of water) is effective. The process of
cleaning and washing will take 3-5 minutes. The
temperature of water should be at room
temperature (270C).
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2. Sorting and Grading This may be done manually
or by using a machine. Fruits are graded on the
basis of their colour, size and weight and sorted
for freeness from damage/ diseases. At the
sorting and grading table, trained workers
wearing gloves sort out the oversized and
undersized fruits, immature/scarred/blemished
fruits, diseased/insect damaged fruits and as
well as fruits with sap injury (in mango) under
the supervision of quality supervisor. The
segregated fruits in the grader machine kept in
plastic crates are removed at the end each
working shift from the process area and are
distinctly labeled for disposal.
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Difference between Sorting and Grading
Sorting Grading
1. Undesirable type of fruits i.e. diseased, damaged, deformed are removed 1. Fruits and vegetables are categorized according to difference in their weight, size, colour, maturity etc.
2. Done primarily to reduce spread of infection to other fruits 2. Done to fetch better price in the market.
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3. Waxing / Coating It is the process of
applying wax on the surface of commodity by
spraying, dip or immersion, brushing, fogging or
foaming. Some fruits develop natural fruit wax on
their surface at the time of maturity. i.e. plum,
apple, citrus, grapes etc. This has its role in
reducing water loss fro the commodity and thus
reducing shriveling and weight loss. While
handling care is taken to touch the fruits as
minimum as possible to retain as much of the
natural wax (also called bloom) on the fruit.
Types of waxes Paraffin wax, carnauba wax,
bee wax etc Examples of some commercial
formulations Tal-Prolong, Semper Fresh for
apple, Frutox, Waxol, Nipro fruit wax for apple,
and citrus, Ban seel for banana, Nu-coat flo for
citrus, Brilloshine L for apples, avocado, melons
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• Advantages of waxing
• Improve appearance of fruit
• Reduce moisture loss by 30-50 and retards
  wilting/ shriveling
• Heals minor injuries
• Protects fruits from minor infections
• Provides modified atmosphere and increase shelf
  life
• Acts a carrier for various chemicals etc

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• 4. Pre-cooling
• It is the prompt cooling of the commodity
  immediately after harvest (generally within 24
  hrs of harvest), to its safe storage temperature
  , which aims at removal of field heat.
• Rate of cooling depends on
• Initial product temperature
• Rate of flow of cooling media around the
  commodity
• Temperature difference between produce and
  cooling media
• Thermal conductivity of produce
• There are different cooling methods followed for
  different commodities. Some fungicides may be
  mixed in water during hydro-cooling to reduce
  decay incidence Weight loss during forced air
  cooling can be reduced by maintaining high (95)
  relative humidity in the pre-cooling chamber

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• 5. Chemical treatment
• Various chemicals are applied to fruits and
  vegetables in order to control postharvest
  diseases and pest infestations.
• Methods of application of chemicals
• Dipping The commodity is immersed in water
  containing appropriate concentration of chemical
  which is toxic to the pathogen. However, the
  concentration of chemical should not be toxic to
  the fruit/ vegetable and should not endanger
  public health. For improving the efficacy of the
  dip treatment and better surface coating some
  wetting agents may also be added. The
  effectiveness of the fungicidal solution may also
  be enhanced by hearting the water in which the
  fruit is being dipped. 500 ppm of benomyl in
  water at 50-55 min, for 2 to 15 min is effective
  for controlling anthracnose in mango without
  damaging the fruit.

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• Methods of application of chemicals (-cont-)
• ii. Cascade application Commodity is passed
  below a shower of shower of diluted chemical.
• Electrostatic sprays Applying the chemical as a
  spray but producing very fine particles and then
  charging them in an electrostatic sprayer so that
  they readily stick to the commodity underneath
  them. The fine droplets of chemical solution have
  same charge and thus they repel each other and
  are attracted towards earth during field sprays.
• Dusting Active chemical is diluted with an inert
  powder i.e. talc for uniform application and
  reduced wastage.
• Fumigation Sulphur dioxide fumes are sued for
  controlling postharvest diseases in grapes.
• Chemical pads Paper pads impregnated chemical
  are used for wrapping the fruits and vegetables
  and control postharvest diseases.

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6. Curing It is technique where the commodity is
left in the field itself in a heap under shade
for few days. It is an effective operation to
reduce water loss during storage from hardy
vegetables viz., onion, garlic, sweet potato etc.
In case of onion curing is a drying process
intended to dry off the necks and 2-3 outer
scales of the bulbs to prevent the loss of
moisture and the attack by decay during storage.
The outermost layer, which may be contaminated
with soil, usually falls away easily on curing.
The dry under-layer should have an attractive
appearance. Onions are cured generally when they
have lost 3 to 5 of their weight. Generally, are
dried in the field by stacking in a warm, covered
area with good ventilation. However, in cool and
moist climates, onions are cured with artificial
heat blown through a duct at 30oC. Onions can
also be cured by tying the tops of the bulbs in
bunches and hanging them on a horizontal support
of pole, wire etc. pole in a well-ventilated and
shaded place. Curing in shade improves bulb
colour.
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• The essential conditions during curing are
• Heat ( 30oC)
• Good ventilation
• Low humidity

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• 7. Irradiation
• Irradiation is a treatment given to various
  fruits and vegetables to control different
  postharvest diseases and disorders. Fruits are
  exposed to various doses of electromagnetic
  radiations for small durations (few sec to few
  min.) of time under highly controlled conditions.
  The unit for measuring radiation dose is Gy or
  rads. It is very effective treatment but in many
  of the cases, the technology of irradiation finds
  a limited commercial application due to the
  following reasons
• either some cheaper and more effective
  alternatives are available
• the irradiation treatment leaves undesirable
  effect on the produce and cause abnormal
  ripening.

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Commercial applications of irradiation
Crop Control of Disease/disorder/pest Min. dose (kGy)
Apple Scald/ brown core 1.5
Apricot, peach, nectarine Brown rot 2
Banana Ripening inhibition 0.30-0.35
Lemon Penicillium rot 1.5 -2.0
Mushroom Inhibition of stem growth and cap opening 2
Orange Penicillium rot 2
Papaya Disinfestation of fruit fly 0.25
Pear Ripening inhibition 2.5
Potato Inhibition of sprouting 0.08-0.15
Strawberry, grape Grey mould 2
Tomato Alternaria rot 3
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8. Vapour heat treatment This was developed to
control infections of fruit flies in fruits. The
treatment consists of stacking the fruits in
boxes in a room which is heated and humidified by
injection of steam. The temperature and exposure
time may be adjusted depending upon the stage at
which the fly is to be killed i.e. egg, larvae,
pupa or adult. The most difficult stage to
control by VHT is larval stage as the insect goes
further into the fruit and away from the surface
thus requiring high temperatures for short time.
Generally the treatment of citrus, papaya, mango
or pineapples may be given at 43o C in saturated
air for 8 hrs followed by maintaining the
temperature for further 6 hrs.
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8. Desapping Desapping of mango fruits is
carried out in processing area by trained workers
under the supervision of processing supervisor.
Desapping is done by holding the mango fruits
upside down while cutting the stalk of fruits.
The stalks of mango fruits are cut very carefully
to 0.5 to 1.0 cm by trained workers by using a
scissor with sharp long nose to avoid causing
skin injury. For exports, the pedicel of the
fruits is cut approximately at a length of 1 cm
from the fruit with the help of sharp scissors
and fruits are kept up side down in special
knitted pallets, for two hours so that the latex
flows out from the fruit completely. Care should
be taken that the latex drop does not fall on the
fruit.
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Let us sum up

• Pre storage treatments are the treatments given
  to a commodity (fruits and vegetables in present
  context) generally after harvesting to reduce
  postharvest losses, enhance storage life and
  retain quality.
• Cleaning removes adhering dust, dirt, extraneous
  matter, pathogenic load etc. from the surface of
  a commodity. Dusting, washing etc. are methods of
  cleaning.
• Fruits are graded on the basis of their colour,
  size and weight and sorted for freeness from
  damage/ diseases. Waxing is the process of
  applying wax on the surface of commodity by
  spraying, dip or immersion, brushing, fogging or
  foaming.
• Pre-cooling is the prompt cooling of the
  commodity immediately after harvest (generally
  within 24 hrs of harvest), to its safe storage
  temperature , which aims at removal of field
  heat.
• Chemicals are applied by spraying, dusting,
  dipping etc. for reducing disease incidence
  during storage. Irradiation is application of
  radiation under controlled conditions. For
  reducing incidence of disease or disorders.