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Preervation by Low Temperature
1. PRESERVATION BY LOW TEMPERATURE
REFRIGERATION
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2. REFRIGERATION
● One of the first application of mechanical refri.
Was to preserve food
Refrigerated storage
Cool Storage Frozen storage
3. COOL STORAGE
Sources of spoilage in a harvested product –
●autolysis
● microbes
● rodents,
● worms,
● mechanical damage.
● Refri. Doesnt make any irreversible changes.
● Slows down all kind of spoilage processes.
4. REFRIGERATED GAS STORAGE
● In addition to low temp., Gas composition
control (CO2 and O2).
● It increases shelf life.
● If CO2 level goes beyond critical limit, internal
physiological breakdown leading to rotting.
● Soln is wrapping the fruits with tissue paper
impregnated with colourless odouless mineral
oil.
6. I. Control of humidity
● Uses direct expansion system
● Refrigerand inside coils expands by
absorbing temperature from product.
● Temp. Gradient causes water loss.
● Indirect expansion is preferred.
● Control of RH is important for long term
storage of commodities.
7. II. Control of ethylene
● Ethylene is a plant hormone which induces
ripening and senescence.
● Ripended fruit emits more ethylene.
● Hence it should not be stored with unripen fruits
which are sensitive to ethylene.
● Usually ventillation is provided in order to
remove ethylene.
● If ventillation is not feasible, ethylene can be
destroyed by oxidation.
8. II. Control of ethylene contd..
● Potassium permanganate held on an inert
substrate is generally used for this pupose.
● UV light is also an industrially used alternative.
● The intermediate compounds formed during
ozone formation destroys ethylene.
● Research about catalytic converters is being
done( Platinum).
9. III. Control of chilling Injury
● Chilling injury dependent on temperature
and time of exposure to that temp.
● Early stages of chilling injury are reversible.
● Some products tolerate chilling injury
without symptoms if the time of exposure is
short.
● There are a number of methods available
to limit chilling injury.
10. III. Control of chilling Injury
contd..
These include
● Stepwise reduction in storage temp.
● Intermittent warming during storage.
11. IV. Temperature
● Temperature control helps to prevent chilling
injury
● Storage temperature varies from product to
product.
● Each 10 deg rise results in doubling of rate of
enzymatic reactions and microbial spoilage.
12. Temp & RH for some produces
PRODUCE TEMPERATURE( deg c) RELATIVE HUMIDITY
Apple -1-4 90-95
Avocado 7 85-90
Black berries -0.5-0 90-95
Grapes(American) -0.5-0 85
Jackfruit 13 85-90
Beans,dry 4-10 40-50
Broccoli 0 95-100
Carrots, mature 0 98-100
Cucumber 10-13 95
Okra 7-10 90-95
15. LOSSES ...
● About 30% of f&v grown in India gets wasted
● 40 million tonnes
● 13 million US $
16. Losses due to..
● Gap in cold chain
● Insufficient storage capacity
● Unavailability of cold storages near farms
● Poor transportation facility
● Lack of processing technology and facility
18. REFERENCES
Wisemax & Lockhart, Fruits and vegetable
preservation, p 138-139
Lisa kitinoja& A. Kader, 2003, Small scale post
harvest hhandling practices: A manual for
horticultural crops, 4th edition, p 133-138
Chilukuri Maheswar, Post harvest losses due to
gaps in cold chain in India- A solution, 2006