CONTRIBUTORS
INCORPORATING COLD CHAIN
Ethylene gas – The silent killer of
produce and flowers
By Jan Lievens
Taking perishable products, whether fruits, vegetables, or fresh cut flowers, from
the field safely to the home is a tricky business.
Postharvest handlers must do
everything they can to maintain the
best possible environmental
conditions for those delicate parcels.
When considering the control of
environmental conditions, never overlook
the power of ethylene gas – Mother
Nature’s silent killer.
WHAT IS ETHYLENE GAS?
Ethylene gas (C 2
H 4
) is a natural growth
hormone that is produced by plant
tissue as well as the combustion of
synthetic materials. It is the only member
of its class and has the simplest structure
of all plant growth substances.
Its impact on the postharvest industry
is tremendous because it is active at
exceptionally low concentrations and
effects plants in so many ways. Ethylene is
involved in a plant’s growth process from
seed germination to its eventual death.
Since a harvested
plant is a wounded
plant, that means most
perishable storage
areas are virtual
ethylene factories.
Unlike most plant hormone compounds;
ethylene is a gaseous hormone. Even
moderately high concentrations of the
gas cannot be seen or smelled, making it
impossible to detect without mechanical
measuring devices.
Ethylene is not harmful or toxic to
humans, however, at extremely high
concentrations it is combustible. Natural
law is a powerful force. Ethylene gas has
a job to do which cannot be reversed,
no matter how hard one tries. That job
is to help a plant through the natural
process of growth and dying.
That is a good thing when the plant is
growing in the earth – death and decay
of all plants is necessary for healthy
ecosystems. But death and decay of
perishables in postharvest storage areas
means loss of viable product and a
large amount of money.
WHAT DOES ETHYLENE GAS DO?
Some of the most detrimental effects
of ethylene are abscission (shedding)
of leaves and flower petals of fresh cut
flowers, hastened senescence (aging)
of all types of plants and accelerated
ripening of fruits and vegetables.
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Abscission is the separation of an organ
or plant part from the parent plant.
Ethylene is a stimulant for abscission
and is particularly harmful to the floral
industry.
Fresh cut flowers that are exposed to
ethylene gas will lose their leaves and
petals faster than those that are stored
in an ethylene-free environment. Not
only does this hurt flower sales by giving
the flowers an undesirable appearance,
but scars left from abscission of leaves
and petals make the plants more
susceptible to disease.
Senescence is the last phase of
plant and extends from full maturity
to death. It is the slowing down and
eventual end of a plant’s metabolism,
which characterises it as a living thing.
The result is discoloration, unpleasant
odours, shrinkage and the general
rotting of produce and flowers.
Ethylene is one of the hormones that
naturally brings about this last phase of
a plant’s life. When fruits, vegetables
and flowers are stored in enclosed
areas, and the ethylene levels build up,
plants senesce, or age, at an unusually
fast pace. In practical terms, the postharvest
‘life’ of the product is cut short
and it must be discarded as waste.
Ripening is the phase of a plant just
before senescence. It is the time in
which the fruit of the plant changes
colour and develops the flavour, texture
and aroma that makes it best suitable
for consumption.
The effects of ethylene on ripening
must be given attention. On one hand,
ripening is important to the sale of
produce. Consumers want to purchase
food they can eat and not have to wait
for it to ripen. But on the other hand,
once the ripening process begins it
cannot be reversed or stopped – only
slowed. So, the quicker the produce
ripens after it is harvested, the less time
there is to get it to the consumer and
the greater the chance of it moving on
to the senescence phase and rotting.
In a natural setting, when a plant
is growing in the earth, the ripening
process is triggered when the internal
ethylene concentration of a plant’s
fruit is 0.1-1 ppm. However, plants
cannot distinguish between internal and
external sources. Any external ethylene
gas that the produce is exposed to will
speed up the ripening. To keep produce
from ripening too quickly, as much
ethylene as possible should be removed
from the surrounding air.
Most wounded plants give off
ethylene gas. The gas evolves naturally
from plant material that is rotting,
ageing, or ripening. Since a harvested
plant is a wounded plant, that means
most perishable storage areas are
virtual ethylene factories.
But plants are not the only producers
of ethylene. It is produced when almost
any material is incompletely combusted
or burned. Some common external
sources are trash burning, fluorescent
lights, cigarette smoke and exhaust
fumes. It also comes from certain fungi,
like botrytis, and other micro-organisms.
Pure automobile exhaust contains about
400 ppm of ethylene. So opening doors
to vent out ethylene in urban, air-polluted
areas could let high concentrations back
into the storage area.
Plants respond to external ethylene
by producing more themselves, a
process called autocatalytic ethylene
production. Just a small amount of the
Consumers want to purchase food they can eat and not have to wait for it to ripen.
Jan Lievens, born in Belgium, is
a graduate civil engineering(B)
and international senior
consultant for engineered
applied postharvest technology
at UTE South Africa. With over
20 years of experience in this
field, he is widely regarded
as a specialist in the fruit-,
vegetable- and flower industry
with regards to humidity,
airborne bacteria and ethylene
removal, both locally and
internationally. Furthermore, he
also designed airflow-friendly
packaging systems for the
industry with proven results.
gas, when added to a produce or floral
storage area, can result in extremely
high levels. Cleaning as much ethylene
out of the air as possible is the best way
to cut down on premature ageing and
ripening and prolong the post-harvest of
life of fruits, vegetables, and flowers.
The quality of produce kept in storage
may suffer in many aspects due to
improper storage conditions. Mold, rot,
premature ripening, shrivel, and weight
loss are among the undesirable effects.
While high relative humidity helps to
eliminate shrivel and weight loss, the
challenges caused by airborne bacteria
and ethylene (a natural ripening
hormone) require a special treatment.
This is when the positive effects of
Miatech’s Bio Turbo are most beneficial.
It uses a patented four stage process
to eliminate ethylene gas, airborne
bacteria and mold spores. It successfully
prevents mold growth, eliminates
unpleasant odours, and reduces
unnecessary losses while preserving
natural freshness and quality.
Unlike some methods, the
performance of the Bio Turbo is not
affected by the high humidity levels
associated with perishable storage.
Can you really afford to work without
technology to protect your reputation
and profits?
Covid-19 circumstances forces
everybody to work with technologies in
your businesses to achieve the benefits
that will keep you competitive in today’s
and tomorrow’s marketplace. CLA
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www.coldlinkafrica.co.za COLD LINK AFRICA • October 2020