Lake Alfred AREC Research Report-CS75-6
REGULATION OF FRUIT RIPENING WITH ETHYLENE
Charles R. Barmore
University of Florida, IFAS
Agricultural Research and Education Center,,
Lake Alfred, Florida 33850 i
Much misinformation about the use of ethylene gas for agricultural
purposes has been spread not only throughout the indutSy- al6 h gh-
out the media dealing with the consuming public. Thi-s-has-developed pri-'
marily because the gas has been improperly used many times, and when done
so, it can be dangerous to people and harmful to produce-. Ethylene gas is
explosive only between concentrations of 3.02 to 34% (30,020 to 340,000 ppm).
As a comparison, the concentration suggested for agricultural purposes is
1 to 100 ppm. As a point of interest, ethylene was once used as an impor-
tant anesthetic; it is not toxic to people.
The primary-commercial source of ethylene is from gas cylinders.
However, use of this source is not advised unless an acceptable metering
system and treatment room design are used. Recently, catalytic generators
have become very popular for supplying ethylene. These units produce
ethylene from alcohol. They are relatively safe but do not offer adequate
concentration control. To ensure safe use of ethylene regardless of source,
an ethylene detector is a must. These units are commercially available,
quite inexpensive, and very easy to use.
The first reported use of a gas for agricultural purposes dates back
to 1910 when Cousins reported an effect of a gas produced by oranges in
storage on ripening of bananas. This gas was later identified as ethylene,
and since that time, use of ethylene has spread to many other fruit operations.
Ethylene is a normal metabolic product of most fruits. However, the
amounts produced by any specific type of fruit varies considerably. The
internal ethylene concentration of citrus fruits is as low as 0.1 ppm as
compared to a high concentration in apple fruits of 2,500 ppm. Under stress
conditions caused by chemicals, insect damage, temperature extremes, diseases,
mechanical wounding, etc., ethylene production will increase rapidly. During
the ripening phase of climacteric-type fruits such as apples, pears, avocados,
and mangos, ethylene production also increases.
Table 1. Internal ethylene concentrations reported in
several types of fruit (From Abeles: Ethylene
in Plant Biology, 1973).
Orange 0.1 to 1.0
Apple 25 to 2,500
Avocados 29 to 74
Banana .05 to 2.1
Mango 0.04 to 3.0
Tomato 3.6 to 30
Peach 0.9 to 20.7
Regulation of Fruit
Ripening with Ethylene
Plant tissue, both vegetative and reproductive (fruits) show a multi-
plicity of responses to ethylene, several of which can be beneficial to the
agricultural industry. For example: the initiation of flowering of pine-
apples is caused by ethylene, the loosening of the citrus fruit to facilitate
mechanical harvesting, the hastening of color development of citrus fruits
and tomatoes, and the initiation of ripening of bananas are all responses
to ethylene. Recently, ethylene has been approved as an agent for germinating
stubborn weed seeds to facilitate the effect of herbicides. The key to
achieving maximum success with ethylene for whatever the end desired, is
having a reasonable understanding of how ethylene works and how to control
The remaining portion of this discussion will be limited to examining
the use of ethylene for the regulation of fruit ripening. This is probably
the primary use of ethylene in the agricultural industry today.
Fruit Ripening and Control by Ethylene
Before this topic can be adequately discussed, several terms which are
very important in understanding the process of ripening must be defined.
Moreover, all fruits do not follow the same pattern of changes normally
associated with ripening, nor will all fruit-ripen to edibility at various
stages of development.
Mature fruit: Fruit which has completed all processes of
development to the point that it is capable
Ripening: Processes which qualitatively transforms the
mature fruit from a nonpalatable to a palatable
or edible condition.
There are two distinct types of fruit with regard to the pattern of ripening
These fruit are characterized by a rise in
respiration during the ripening process.
In addition, there is a distinct and ob-
servable sequence of changes such as color
development, softening, aroma, etc. Several
fruit of this group are avocados, apples,
pears, tomatoes, mangos, banana, and figs.
Nonclimacteric: These fruit do not exhibit the distinct
rise in respiration during ripening, and the
separation between maturation and ripening
is often difficult to distinguish. Citrus
is this group.
The following graph more clearly differentiates between climacteric and non-
Regulation of Fruit
Ripening with Ethylene -3- Research Report-CS75-6
,-.- PRIME EATING QUALITY
N AON- CLI. ACTERIC INEDIBLE
SGROW;G F HARVESTING SEASON --
CLIMACTERIC AND NON-CLIMACTERIC LIFE CYCLES
(From: Grierson, International Institute for
Refrigeration, Commission C-2, 1973.
The process of ripening is extremely complex involving numerous
physiological and biochemical changes. Some of the most obvious changes
2. Color development
3. Development of sweetness
4. Production of volatiles
5. decrease in acidity
6. Reduction in astringency
In some fruits, the ripening process is initiated as soon as the fruit
matures on the tree; in others, the process is delayed-until after picking.
The rate at which the ripening process proceeds under optimum ripening con-
ditions is an inherent characteristic of that particular fruit and is
normally "triggered" by ethylene produced within the fruit itself.
There is no exception to the observation that ethylene cannot promote
the ripening process of many fruits as long as the fruit is receptive to
ethylene. Numerous studies have shown that maintaining fruits such as
mangos, avocados, and apples in an ethylene free environment will delay
ripening. However, this does not mean that ripening is controlled entirely
by ethylene. This is because that as fruit "ages" on reaching maturity,
less ethylene, either in amount or exposure time, is required to promote
The amount of ethylene required to promote ripening of most fruits is
normally 0.1 ppm for a threshold response, 1 ppm for half-maximum response,
and up to 100 ppm for a saturating dose. Generally speaking, after a max-
imal response to ethylene is reached, higher concentration or longer exposure
time have no additional effect.
Regulation of Fruit
Ripening with Ethylene -4- Research Report-CS75-6
The effect of ethylene on the promotion of fruit ripening is to speed
up the process. In essence, it acts as a catalyst. It in no way alters
the ultimate course of ripening. Some of the more common uses of ethylene
in the fresh fruit and vegetable industries are degreening citrus fruits
and promotion of ripening of both tomatoes and bananas. In contrast to
these uses of ethylene, removal of ethylene from storage units during
extended storage is important to prevent premature ripening of some types
The use of ethylene gas for postharvest purposes requires proper
planning and design of ethylene treating equipment to achieve maximum
benefit. All ethylene treating rooms should be equipped with: an ethylene
metering system in order to maintain a specific concentration during the
treating period, adequate ventilation to maintain proper carbon dioxide
and oxygen concentration, exact temperature control, and humidity control.
If these prerequisites are not met, the response by the fruit cannot be
predicted or controlled.
The importance of the quality of fruit to be treated cannot be over-
emphasized. The final product of ethylene treated fruit is no better than
that which could have been attained under natural ripening conditions.
Immature fruit will respond to ethylene, yielding responses characteristic
of ripening, but the fruit will not develop the flavor qualities of a
ripened mature fruit. In some cases, color development will not proceed
Several methods for treating fruit with ethylene have been used. How-
ever, the most reliable and accurate system in use today is a metering
system of the following design:
2-stage Shut-off Single
Gas cylinder *" regulator valve stage -- Solenoid
Room --* Flowmeter
This system is designed for continuous or intermittent use. Safety devices
are designed into the system to ensure that the ethylene concentration does
not reach dangerous levels. Concentration control is the key to this system.
To use this system, the treatment room must be properly designed for adequate
ventilation (one room air exchange/hr.) and air circulation as high as once
per minute. "All parts for this system are commercially available.
Treatment Conditions for Mangos
The method reported in the Proceedings of the Florida State Horticultural
Society 87: 331, was designed.for treating mangos for local sale. At that
time, there was no apparent interest in shipping ethylene treated fruit.
However, this season the interest has been overwhelming. Since ethylene
speeds up the ripening process, conditions for treating mangos were modified
to prevent too early ripening during shipment. It is suggested that the fol-
lowing conditions be used when treating mangos:
Regulation of Fruit
Ripening with Ethylene -5- Research Report-CS75-6
1. Ethylene concentration: 10 ppm
2. Temperature: 70 F
3. Humidity: When using cartons, 90%; when using bulk
4. Treatment time: 24 hrs. The treatment time should be
reduced as the ripening time of nonethylene treated fruit
decreases as the harvest season progresses for that
particular cultivar. Treatment time for the last
picking of a given cultivar if desired should not
exceed 12 hrs.
5. Storage after treatment: 600 F
6. Ventilation: One room air exchange every 1 to 2 hrs. This
prevents CO2 buildup which will reduce the effectiveness of
7. Ripening temperature: 70 to 750 F
Low treatment and storage temperatures contribute to the development of
the yellow pigment. Higher temperatures partially inhibit the synthesis
of this group of pigments.