Transcript control_atmosphere_ca_and_modified_atmosphere

Control atmosphere (CA) and Modified
atmosphere (MA) storage
• Fruits and vegetables are still alive after harvest, it is necessary to
restrain their respiratory activity.
• Metabolic activity cases, colour, flavour, aroma and softening
changes in commodities. The energy needs usually obtained from
respiration.
• Respiration is basically characterized by O2 consumption and Co2
emission.
• Control of respiration
• 1-Storing at low temperatures.
• 2-Usinge chemicals i.e. 1-MCP
• 3-Controlling the atmosphere surrounding the harvest produce.
• 4-Combination of them.
Control atmosphere (CA) and Modified
atmosphere (MA) storage
• Extended shelf life
• 1-Harvesting at optimum maturity, minimum mechanical injury,
proper sanitation procedures, and optimal temperatures and RH are
maintained.
• 2-Modification and control of O2, Co2 and ethylene surrounding the
produce to level different from those in normal air.
• 3- This modification is commonly based on the effect of low O2 or
moderate Co2 to restrain respiration, because both O2 and Co2 are
biological-active molecules that play a decisive role in primary and
secondary metabolic processes in plant organs.
• Their global influence on metabolism has led to their use for
modification of plant behavior with the purpose of extending both
storage duration and shelf-life.
Modified of the atmosphere
• The principle of storage of fruits and vegetables under a MA consist
of a change of the quantitative relation of the normal ambient air
components by eliminating or adding gases in a refrigerated and
gastight area.
• Depending on how the modification of the atmosphere is reached
and applied, this technique is known as control atmosphere (CA) or
MA.
• CA storage consists of a permanent stable control of the gas
composition that surrounding produce during refrigerated storage or
transport at optimal temperature and RH in an airtight cold room or
container.
• MAP When the generation and stabilization of favorable atmosphere
are obtained by packaging refrigerated produce in closed polymeric
films of reduced dimentions (bags, boxes, pallets), the technique is
called MAP.
The beneficial effects of CA and MAP
depend on:
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Produce itself (Species).
Cultivar.
Growing conditions.
Harvesting system.
Physiological stage.
Post-harvest handling.
Gas composition.
Storage temperature and
Time
Beneficial effects (MAP)
• 1-O2 delays ripening at <8 kPa, lower the O2 concentration the,
greater the effect.
• 2-Higher CO2 levels (above 1 kPa) decrease or inhibit ethylene
Reduced biosynthesis. These effects are additive to those of
reduced O2 atmosphere.
• 3-MAP limits softening by decreasing lignification or inhibiting
polygalacturonase activity.
• 4-Colour preservation by the inhibition of important reactions in a
number of tissues i.e. chlorophyll degardation.
• 5-MAP also seems to preserve nutritional value (Organic acid,
Vitamine A and C. No sugar changes
• 6-Reduction of chilling injury.
• 7-Very low O2 (0.5 kPa) and very high CO2 (>40 kPa) levels have
the potential to act as insect control.
2-Benefical effects (MAP)
• 8-MAP can replace or reduce the dose of certain postharvest
chemical e.g. diphenylamine or daminozide against scald in pears
and apples.
• 9-Prolong the pre-climacteric and climacteric periods and therefore
produce can be harvest in a physiological stage closer to full
maturity to ensure better sensory characteristics.
• 10-The use of essential oils (eucalyptol, eugenol, mentol or thymol)
seems to improve the benefical effects of MAP.
• 11- After MAP effects (respiration, softening, colour change ..).
Detrimental effects
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• Physical
Plastic film can reduce the rate of cooling.
Potential increase of water condensation within packages.
It is impossible to act externally on the gas composition.
• Physiological
Abnormal ripening of certain fruit (banana, pear, tomato).
Development of some physiological disorders such as brown stain of
lettuce, internal browning and surface pitting of pome fruit and celery.
Development of off-flavours and off-odours due to the accumulation of
ethanol and acealdehyde.
Decreasing in vitamins i.e. VC in artichocke
Decrease in total anthocyanin content of pomegranates.
Limits of MAP
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1- The use of MAP is not good enough for mixed vegetable for soups
(parsley, celery, sliced zucchini and carrots, pieces of cabbage).
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The limits of tolerance of fruits and vegetables to high CO2 levels decrease
with decreased O2 levels
Mechanism of CA effects on respiration
• In asparagus and broccoli under CA
storage using more acid rather than sugar.
• Therefore, delays the senescence-related
increase in plasma membrane
permeability
Other beneficial effects of MAP rather than
respiration
• Ethylene synthesis: 1-ACC to Ethylene by
ACC-oxides need O2.
• The K1/2 O2 is 1.4-10 kPa (as ACC levels
increase, the k1/2 of the enzyme for O2
declines).
Secondary metabolic pathways
• Low O2 reduce the rate of degreening due to chlorphyll
loss, and inhibits browning reactions catalyzed by
polyphenol oxidase (PPO). The O2 levels below 2
kPa`and above the fermentation threshold of ca. 0.5 kPa
reduced the rate of browning in lettuce.
• Low O2 reduce the accumulation of alfa-farnesene a
semi-volatile sesquiterpene that induce superficial scald.