Fruits and Vegetables Processing Technology (Lecture 03)

1. Fruit & Vegetable Storage
Proper marketing of perishable commodities such as fruits
and vegetables often requires some storage to balance
day-to-day fluctuations between harvest a and sale or for
long-term storage to extend marketing beyond the end of
harvest season.
The principal goal of storage is to control
• the rate of transpiration,
• respiration,
• disease, and insect infestation and
• to preserve the commodity in its most usable form for
the consumer.
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2. Storage life can be prolonged by
 harvesting at proper maturity (Figure 1),
 control of postharvest diseases,
 regulation of atmosphere, chemical treatments,
 irradiation, refrigeration,
 controlled and modified atmospheres, and
 by several other treatments.
• The main goals of storage are to
(I) slow the biological activity of fruits and vegetables without
chilling injury;
(2) slow the growth of microorganisms,
(3) reduce transpirational losses.
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4. • A. PRINCIPLES OF STORAGE
• Since all fruits and vegetables are living tissues, the tendency
after harvest is to continue respiration.
• Thus, proper and adequate storage conditions must be
maintained, otherwise
the following undesirable processes may occur in certain
vegetables:
 1.Sprouting—potatoes, onions, ginger, garlic
2. Elongation—asparagus, carrots, beets,
 3. Rooting—due to increased humidity which may result in
rapid decay, shrivelling, and exhaustion of food reserves
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5.  4. Greening—exposure of potatoes to light during storage
may produce green tissue and synthesis of toxic
glycoalkaloids such as solanine and chalkonine
 5. Toughening—green beans, sweet corn may toughen due
to prolonged storage at relatively high temperatures
• The Following factors need to be considered for success of
produce storage.
 1. Temperature
Temperature in a storage room should normally be
maintained at the desired temperature for commodities
being stored.
 Delay in cold storage reduces marketability of fruits and
vegetables)
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6. • Temperature variation within the room is minimized by
incorporating adequate amounts of insulating material
in the walls and by maintaining adequate levels of air
circulation in the room.
• When the room is filled, the containers should be
stacked to allow an air passage along at least one side of
each container.
• Thermostats are placed at a height of five feet from the
floor for ease in checking locations.
• A calibrated thermometer should he used to periodically
check the thermostat.
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7. 2. RELATIVE HUMIDITY
• For most perishable fresh fruits and vegetables, the relative
humidity should be maintained between 90 to 95%.
• The relative humidity below this range will result in a
moisture loss from the produce (Table 1).
• Thus the produce will be shrivelled and limp. Relative
humidity if higher than 90% may cause excessive growth
of microorganisms.
• Refrigeration equipment must be especially designed to
maintain a higher relative humidity.
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9. • The environmental factors of temperature, relative humidity
and vapor pressure deficit are important in the storage life of
fruits and vegetables.
• A 5 to 10% loss in weight of produce results in shrivelling,
which makes the produce look stale and unattractive to sell.
• By using high relative humidity during storage, care must be
taken to prevent the growth of surface microorganisms
• 3. ATMOSPHERIC COMPOSITION
• The atmospheric composition in a storage room is controlled by
addition of gases allowing the commodity to produce or
consume gases or by physically or chemically removing
undesirable gases from the storage room.
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10. • Gases such as carbon monoxide (CO), carbon dioxide (CO2),
ethylene (C2H4), and nitrogen (N2) can be added to a facility
from a bottled supply (or dry ice in the case of C02) or produced
by on-site generators.
• As the perishable fruits and vegetables undergo respiration,
they consume 02 and release CO2.
• This effect can be successfully used to control the desired
concentration of these gases in storage.
• High concentration of undesirable gases are removed by
scrubbing devices.
• For example, CO2 can be absorbed in water or lime;
• C2H4 and other volatiles can be removed by potassium
permanganate, catalytic oxidation or UV light; and 10

11. • O2 can be removed by using it in a combustion process or by
a molecular sieve.
• In certain cases external concentrations of gases are desirable
and the accumulated gases can be adjusted by ventilation.
• 4. LIGHT AND OTHER FACTORS
• Exposure of potato tubers to light in grocery stores can
synthesize glycoalkaloids (solanine and chalkonine) which
are toxic to humans.
• Likewise, other factors such as herbicides, fungicides,
pesticides and growth regulators may affect the produce and
may have harmful affects on humans.
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12. Storage system
1. Natural Storage
• Vegetables such as potato, sweet potato, and garlic are
kept underground for several months.
• They are harvested prior to the rainy season for a better
market price.
• This harvesting does not involve extra expenditure and
building for storage.
2. Artificial Storage
• Pits or trenches are dug underground for storing beets,
potatoes, onions, carrots, turnips, cabbages, and sweet
potatoes where they are covered with straw and soil until
there is a market demand (Figures 2 and 3).
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14. 3. Ventilated Storage
• Cellars are underground rooms with slanting roofs covered
with sods and soils.
• The structure may be built into the hillside and covered
with additional soil.
• Cellars are provided with heaters and dry atmospheres
during winter months.
• Potatoes, turnips, carrots and beets are stored with high
relative humidity at (1 .7—4.4°C).
• Where snow is prevalent, a good cellar will provide
satisfactory storage for hard vegetables and fruits. Above-
ground warehouses may be used to store produce.
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15. • In cold weather the produce is covered with blankets to
protect from cold temperatures.
• Ventilation is essential for good storage.
• Potatoes, onions, garlic bulbs, crucifer leafy vegetables and
fruits are stored successfully.
• This storage structure has several advantages over other
types:
 (I) special construction is not needed;
 (2) produce is easily handled;
 (3) grading, storing, packaging of fruits and-vegetables is
facilitated;
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16.  (4) air may be humidified; and
 (5) fans can be controlled manually or automatically with a
thermostat.
4. Ice Refrigeration
• An advance on the above-ground warehouses was the use of
ice as a refrigerant.
• Lower temperatures obtained enable longer storage of meat
and perishable fruits and vegetables.
• The melting of 1 kg of ice absorbs 325 kilojoules.
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17. • However, removal of melted ice water is a disadvantage.
• The introduction of a small ice box was a great advance on
the domestic level, and for small-scale commercial storage
of fruits and vegetables.
• II. MECHANICAL REFRIGERATION
• Refrigerated storage makes possible the marketing of
perishable fruits and vegetables beyond their harvest season.
• In developed countries, most of the fruits and vegetables are
available year-round to consumers.
• This is due to the refrigerated storage.
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18. CONTROLLED AND MODIFIED ATMOSPHERE STORAGES
• The principle of storage under high CO2 and low O2 appears to have
been applied in ancient times.
• Controlled and modified atmosphere storages (CA and MA) indicate
the removal or addition of gases resulting in an atmosphere
composition for fruits and vegetables and their products that is
different that of air (75% N2, 21% O2 and 0.03% CO2) .
• MA and CA differ in the degree of control;
• CA is more exact than MA.
• In MA gases are not controlled at specific concentration.
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22. • Humidity and C2H4 control during CA storage:
• it is also recommended to control both C2H4 and
humidity during CA storage of fruits and vegetables in
addition to controlling of O2 and CO2 and temperature.
• Accumulation of C2H4 will cause degreening and
ripening of fruits and vegetables, so absorption of C2H4
by KMNO4 is advised.
• Also in commercial CA storage humidity reaches to
saturation in storage of some fruits and vegetables and
this may encourage the growth of fungi.
• As a result it is advised to apply a suitable fungicide to
retard the fungi growth.
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23. • Behavior of fruits and vegetables after CA storage:
After the removal of fruits and vegetables from CA
storage, they may have some change like
 increased respiration rate,
 appearance of tissue browning and decease in firmness.
• However, many investigation noticed that the
organoleptic properties of fruits and vegetables after
CA storage is more better than those after refrigerated
storage provided that the CA conditions were properly
selected.
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24. CA storage duration (long or short):
• CA storage for a long time may cause injuries to fruits and
vegetables inspite of the properly selected conditions.
• However, storage life of fruits and vegetables in CA storage
may be 50% longer than in air storage.
• Results regarding the CA storage for short time are of vital
importance specially to be applied in transportation.
• The effect of different levels of O2 or/and CO2 during CA
storage for short time for some fruits and vegetables have been
studied but further research is needed.
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25. • Including of CO in CA storage was found to be beneficial
especially with regard to control fungal decay and to inhibit
discoloration (5-10% concentration).
 Advantages and disadvantages of CA and MA storage:
• the advantages or benefits include
 retardation of senescence,
 reduction of produce sensitivity to C2H4,
 controlling some of the physiological disorders like chilling
injury and also
 controlling postharvest disease and decaying.
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26. • The limitations or disadvantages include
 increasing some of the postharvest disorder like sprouting
in potatoes, brown heart in apples;
 irregular ripening of bananas and tomatoes,
 development of off-flavor and
 in some cases increasing the susceptibility to decay.
• Something of interest in CA storage that there is no single
best combination of CO2 and O2 for mixed storage of fruits
and vegetables.
• Instead each species and may be each cultivar varies in its
CA requirements.
• Tables 6 and 7 show the CA requirements from O2 and CO2
for some of the important fruits and vegetables..
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27. • Storage in polymeric films:
Great progress has been achieved in the field of developing a
produce package for CA storage.
• These packages are perforated and semipermeable and aim
at
 reducing moisture loss,
 protect the produce from mechanical damage and
 improve its appearance.
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28. • In the produce package, respiration occurs by the produce and
permeation by the package.
• In other words the produce takes up O2 and gives CO2, H2H4
and volatiles while the package according to its permeability
permit the escape of these gases.
• However, the package system should be in such a way to
achieve steady state condition where equilibrium
concentration of O2 and CO2 is reached.
• Many factors interfere or affect this steady conditions such as
 the type of produce,
 its weight,
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29.  variety,
 respiration rate,
 stage of maturity,
 temperature,
 O2 and CO2 level needed,
 C2H4 concentration,
 light,
 film thickness,
 film permeability and
 others.
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30. Vacuum storage:
• it may be classified to two types:
 the first include the gas-flush packaging where the air in
the package is replaced by another gas such as CO2 or N2
and it is used for packaging of salads, fruits juices and
minimally processed fruits and vegetables,
 the second type is that where all air is removed and a
vacuum is created.
 High density polyethylene films are used for this purpose
and this packaging technique is utilized for minimally
processed fruits and vegetables.
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31. • Sub atmospheric (low pressure or hypobaric) storage:
• the storage life of many fruits and vegetables can be extended
by reduced pressure under refrigeration due to low respiration
rate and evacuation of C2H4.
• However, the hypobaric storage is a form of CA storage.
• the produce is ventilated by air saturated with water vapor and
containing suitable fungicides in some cases.
• It is of interest to note that at lower pressure storage such as
278 mm Hg or less, microorganism growth retardation is
achieved.
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32. Radurization:
• it is meant by this term the utilization of ionizing radiation
materials such as cobalt, cesium and uranium is utilized.
• Only beta and gamma radiation kinds are utilized in food
preservation;
• beta radiation is used for food pasteurization and in the case
of gamma radiation, it is utilized for food sterilization.
• Retardation of sprouting and rooting by radiation are practiced
commercially.
• In case of pasteurization a dose of 1 megarad is utilized, while
for sterilization a dose higher than 1 Mrad is used.
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