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ruits are widely distributed in nature,
commercially important and nutritionally
indispensable food commodity. Ripening is a process
in fruits that causes them to become more edible. In
general, a fruit becomes sweeter, less green, and
softer as it ripens. However, the acidity as well as
sweetness rises during ripening, but the fruit still
tastes sweeter regardless. An organic compound
involved with ripening is ethylene, a gas produced by
plants from the amino acid methionine. Ethylene
increases the intracellular levels of certain enzymes
in fruit and fresh-cut products, which include (i)
amylase, which hydrolyzes starch to produce simple
sugars, and (ii) pectinase, which hydrolyzes pectin, a
substance that keeps fruit hard. Other enzymes break
1
down the green pigment chlorophyll, which is
replaced by blue, yellow, or red pigment . Ripening
is associated with change in composition
2
i.e.,
conversion of starch to sugar, by which fruits attain
their desirable flavour, quality, colour, palatable
nature and other textural properties. Synthetic
chemicals are being used to ripen them artificially
which hasten the ripening process and make fruits
appear fresher or even longer, particularly during
early and off-season. Fresh fruits are nutritious, but
toxic artificial ripening agents pose health hazards.
For many years, ethylene had been used as a ripening
agent, but nowadays ethane, calcium carbide and
ethephon are commonly used for faster ripening,
inappropriate use of these chemicals to ripen fruits is
associated with many health hazards.
On the basis of ripening behavior, fruits are
classified as climacteric and non-climacteric fruits
(Table 1) . Climacteric fruits, defined as fruits that
enter 'climacteric phase' after harvest , they
continue to ripen. During the ripening process, the
fruits emit ethylene along with increased rate of
respiration. Ripe fruits are soft and delicate and
generally cannot withstand rigours of transport and
repeated handling. These fruits are harvested hard
i.e.
3
Everyman’s Science Vol. L No. 6 February’16- March’16
ARTIFICIAL RIPENING OF FRUITS—MISLEADING
RIPE AND HEALTH RISK
R. U. Abhishek, H. N. Venkatesh, K. Manjunath and D. C. Mohana*
Department of Microbiology & Biotechnology, Bangalore
University, Jnana Bharathi, Bengaluru 560 056, E-mail:
mohanadc@gmail.com
Fruits are highly nutritious and form as key food commodity in the human consumption. Ripening is a
physiological process, which makes the fruit more edible, palatable and nutritious. Nowadays fruits are
deliberately being contaminated by chemicals causing serious health hazards. Synthetic chemicals are
being used to ripen them artificially which hasten the ripening processand make fruits appear fresher or
even longer, particularly during early and off-season. One or more banned chemicals are still being used in
Indian subcontinent and other countries. The food safety problems posed by artificial ripening agents
pertaining to India's fruit trade have been discussed here.
INTRODUCTION
F
Climacteric fruits Non -climacteric fruits
Mango, banana, papaya, guava, sapota, kiwi,
fig, apple, passion fruit, apricot, plum, pear,
Orange, mousambi, kinnow, grapefruit, grapes,
pomegranate, litchi, watermelon, cherry,
raspberry, blackberry, strawberry, carambola,
rambutan, cashew,
Table-1: Few examples of fruits according to their respiratory behaviour at ripening3
etc.
etc.
364
and green, but fully mature and are ripened near
consumption areas. Small dose of ethylene is used to
induce ripening process under controlled conditions
of temperature and humidity. e.g , mango, banana,
papaya, guava, sapota, kiwi, fig, apple, passion fruit,
apricot, plum, pear, custard apple, . Non-
climacteric fruits, once harvested do not ripen
further, they produce very small amount of ethylene.
There is no characteristic increased rate of
respiration or production of carbon dioxide. e.g ,
orange, mousambi, kinnow, grapes, pomegranate,
litchi, watermelon, cherry, raspberry, blackberry,
strawberry, carambola, rambutan, cashew, .
Fruit ripening is an irreversible phenomenon
involving a series of physiological, biochemical and
.
etc
.
etc
organoleptic changes, that finally leads to the
development of a soft edible ripe fruit with desirable
quality. The fruits may require few days to ripen and
this short period seriously limits their transport to
distant markets. With the rapid development of fruit
trade, artificial ripening has become essential. In
order to hasten the ripening process and make fruits
appear fresher or even longer, different chemicals are
utilized for the commercial purposes.
Climacteric fruits like mango, banana, papaya,
sapota and custard apple are often harvested in a
mature but unripe condition and then subsequently
allowed to ripen by natural release of ripening
hormone (ethylene) from the fruit. However, natural
ripening in some fruits is a slow process, which leads
to high weight loss, desiccation of fruits and uneven
ripening. With the rapid development of fruit trade,
artificial ripening has become essential and the
methods practiced earlier by small traders are
smoking and calcium carbide treatment.
Ethylene is a naturally occurring gaseous plant
hormone that is produced by many fruits and
vegetables. It affects the physiological processes in
plants and initiates the ripening process when
internal concentrations increase from 0.1 to 1.0 ppm
(parts per million) . Externally applied ethylene can
also initiate the ripening process. The commonly
ARTIFICIAL RIPENING OF FRUITS
3
used ripening agents are calcium carbide, acetylene,
ethylene, propylene, ethephon (ethrel), glycol,
ethanol and some other agents . For many years,
ethylene had been used as a ripening agent, but
nowadays ethane, calcium carbide and ethephon are
commonly used for faster ripening, inappropriate use
of these chemicals to ripen fruits is associated with
many health hazards.
Globally, the ripening is done through gas
emission systems or ethylene generator systems,
depending on quality and shelf life desired. Use of
ethylene for ripening of the fruit is a common
practice in different countries; but due to high cost
and scarcity in terms of its availability, many
developing countries use low-cost ripening agents
like calcium carbide. Chemicals like calcium
carbide, ethephon and oxytocin are reportedly being
used in fruit and vegetable farms for artificial
ripening of fruits and for increasing the size of fruits
and vegetables, respectively . Calcium carbide is one
of the most commonly used ripening agent for fruits,
while other calcium salts like calcium ammonium
nitrate, calcium chloride and calcium sulfate are used
by local fruit industries to delay the fruit ripening
process. The use of calcium carbide is being
discouraged worldwide, due to associated health
hazards. Calcium carbide treatment of food is
extremely hazardous because it contains traces of
arsenic and phosphorous, and once dissolved in
water, it produces acetylene gas. Acetylene acts like
ethylene and accelerates the ripening process.
Arsenic, phosphorous and acetylene gas may affect
the different organs and cause various health
problems.
The concentration of ethylene required for the
ripening of various fruits vary, but in most cases they
are in the range 0.1-1 ppm. The time of exposure to
initiate full ripening also vary depending upon the
type of fruit. Several chemicals agents are used as
artificial ripeners. The following are the some
4
4
MECHANISM OF ACTION OF RIPENING
AGENTS
1,5
Everyman’s Science Vol. L No. 6 February’16- March’16
365
important sources of ethylene or acetylene
production.
Ethylene regulates the fruit ripening by
coordinating the expression of genes responsible for
enhacing the rate of respiration, autolytic ethylene
production, chlorophyll degradation, carotene
synthesis, conversion of starch to sugars and
increased activity of cell wall degrading enzymes. It
can be produced artificially by gas emission systems
or ethylene generators.
(i) Ethylene generator: Ethanol is heated in the
presence of catalyst to produce
ethylene.
(ii) Ethylene mixture: Ethylene (6%) in carbon
dioxide by weight, to avoid explosion, is
used for fruit ripening.
Ethylene:
Calcium carbide:
Ethephon or Ethrel:
Ethylene glycol:
HE ALT H H A ZA RD S O F B AN NE D
CHEMICALS
When calcium carbide ( ) is
hydrolysed, it produces acetylene, which
acts as an artificial ripening agent. It also
contains trace amounts of ethylene that is
sufficient to be used in fruit ripening.
Ethephon (2-chloroethane
phosphonic acid) is acidic in water and liberates
ethylene in neutral to basic medium (above pH 5.0).
Ethephon penetrates the fruit and decomposes to
ethylene, thereby hastens the ripening process.
Ethylene reacts with hydrogen
peroxide to produce the ethylene glycol. Ethylene
glycol is colorless, odorless and sweet tasting liquid.
Ethylene glycol, when diluted with water, can ripen
various fruits faster than the regular ripening rate of
the fruits, in particular colder climatic conditions. It
can also acts like ethylene in fruit ripening process.
Fruits are still being commercially ripened with
banned chemical like calcium carbide which after
reaction with water vapour present in the
surrounding atmosphere releases acetylene gas.
Calcium carbide is a carcinogenic agent and is
banned in India under Prevention of Food
Adulteration Act-1955 . Although the Act prohibits
6
C H OH C H + H O
2 5 2 4 2
→
CaC
CaC + 2 H O Ca (OH) + C H
2
2 2 2 2 2
→
the use of calcium carbide, this chemical is
commonly used by collectors and traders for the
production of acetylene to induce fruit ripening.
According to the survey of Directorate of Marketing
and Inspection (Ministry of Agriculture,
Government of India) , 99% of the mangoes in India
are ripened by using calcium carbide, as it is the most
economical way for ripening process of mango. In
2013, Jindal from India , reported a case of
accidental poisoning of a 2 year old boy with calcium
carbide, in which the child put paper piece
contaminated with calcium carbide in mouth.
Similarly, calcium carbide related ocular burn
injuries are reported during mango ripening season
of West Bengal in India . Many incidences of this
kind have been reported worldwide. Recently in
2014, the National Human Rights Commission of
India has sought an action taken report from Indian
Health Ministry over use of calcium carbide to ripen
fruits despite a nationwide ban . Some traders ripen
fruits like banana in enclosed chambers where large
quantities of calcium carbide is put and sprinkled
with water before sealing the chambers. Though the
released acetylene triggers ripening process in fruits,
it is an inflammable gas involving risk of fire
hazards. Calcium carbide is also put in small packets
in the fruit boxes and in some cases sprinkled onto the
fruit surface. However, calcium carbide contains
chemical impurities such as arsenic hydride and
phosphorus hydride that are highly carcinogenic
compounds. The method used in the application of
carbide is also hazardous to health, in that carbide
pieces can find themselves among the heaps of fruit.
Further, fruits ripened with calcium carbide though
develop attractive surface colour, but are inferior in
taste, flavour and spoil faster. In 2010, Pandarinathan
and Sivakumar from India reported the biochemical
changes in mangoes artificially ripened by calcium
carbide, which recorded lesser amount of sugars
(reducing sugar, non-reducing sugar and total sugar)
and total soluble solids in the calcium carbide treated
fruits than the untreated .
The chemicals or agents are used to ripe fruits
as early as artificially. Nowadays, several other
7
8
9
10
et al.
11
Everyman’s Science Vol. L No. 6 February’16- March’16
366
chemicals are used as artificial ripeners , carbon
monoxide, potassium sulfate, ethephon, putrescine,
oxytocin, protoporphyrinogen, . Ethephon is an
organophosphate pesticide, so it is not recommended
as a ripening enhancer. Oxytocin is a mammalian
hormone, used as a drug in veterinary medicine
which is not advised for use in fresh fruits and
vegetables . In India, about 60% of the mangoes
harvested early in the season are treated with calcium
carbide, adding that the use of the chemical declines
as the season progresses . In a study, Hakim et al
from Bangladesh reported the higher amount of
heavy metals like lead and arsenic in ethephon-
treated fruit and vegetable samples. Many instances
have been reported that some unscrupulous elements
are following the practise of dipping green
vegetables in artificial colours to give them a fresh,
attractive and pleasant appearance . The other major
contaminants found in fruits are pesticide residues,
crop contaminants, mycotoxins (aflatoxin, patulin,
ochratoxin, .), naturally occurring toxic
substances and heavy metals. Heavy metals are
harmful and become toxic for health if they are taken
above the limit of daily dietary allowance
recommended.
Indian Ministry of Agriculture has clarified that
the fruits exposed to ethylene gas (fruit ripening plant
hormone), in low concentration of 10-100 ppm
exogenously to trigger their ripening, are safer for
consumption . Fresh fruits and vegetables shall be
free from coating of waxes, mineral oils and colours.
However, there is provision for coating fresh fruits
with food additives ., bee wax (white/yellow),
carnauba wax or shellac wax as glazing agent in
accordance with the good manufacturing practice
(GMP) for use of food additives under proper label
declaration.
Chemicals are commonly used for the artificial
ripening of fruits. The use of calcium carbide is
prohibited for the ripening of fruits. Ethylene is
generally recognized as safe (GRAS) by Food and
e.g.
etc
.
etc
viz
12
13 14
7
7
ALTERNATIVES TO CALCIUM CARBIDE
Drug Administration (FDA) of the United States.
Ethylene has been found not harmful or toxic to
humans in the concentrations found in ripening
rooms. Ethylene was used historically as an
important anesthetic in concentrations significantly
greater than that found in a ripening room , at
concentration of 85% with 15% oxygen. It is
flammable and explosive at concentrations above
3%, as a fruit ripening hormone, effective at 0.1 to 1
ppm. One part of ethylene per million parts of air
that's one cupful of ethylene gas in 2,50,000 litres of
air - is enough to promote the ripening process in
fruits However, ethylene is often targeted as the
reason for difficulty in breathing in ripening rooms is
usually due to (i) CO , is produced by the ripening
fruit in the room, levels increase over time and/or (ii)
oxygen levels, is taken in by the ripening fruit. The
increased CO and decreased oxygen levels make
breathing in a ripening room difficult.
Ethrel or ethephon is a commercially available
plant growth regulator, which is a source of ethylene
similar to that naturally released by fruits during
ripening process. Although dipping of fruits in
diluted ethrel solution is recommended for
enhancing ripening, it is a cumbersome process and
may cause some problems if commercially available
ethrel contains chemical impurities . According to
Environmental Protection Agency of the USA,
ethephon has been classified as a Group D
carcinogen based on its cancer-causing potential,
which is reported as inhibitor of cholinesterase. The
Food Safety and Standard Authority of India
(FSSAI) has advised to use only the ethylene in
gaseous form for artificial ripening of fruits. To
overcome these problems, ethylene gas is
commercially used in modern ripening chambers
which requires huge investment and is not
economical for farmers or small traders. Catalytic
reactors based ethylene generators are also available
which produces ethylene gas using ethanol or
methanol or ethrel. Mango fruits exposed to 100 ppm
ethylene gas for 24 hrs can be ripened in 5 days as
compared to 10 days in non-treated fruits without
adversely affecting the quality. Similarly, bananas
i.e.
16.
2
2
1
16
Everyman’s Science Vol. L No. 6 February’16- March’16
367
exposed to 100 ppm ethylene gas for 18 hours can be
ripened in 4 days at room temperature and 6 days at
20°C. Papaya fruits exposed to ethylene gas ripened
with uniform surface colour and uniform firmness in
4 days at ambient temperature . Therefore, use of
ethylene is suggested as a safe alternative to calcium
carbide for ripening of fruits.
Most ethylene gas today is created out of
petroleum products such as natural gas liquids or
crude oil by the use of heat, nitrogen, and steam that
is converted into a liquid gas, and then stored in metal
containers used for dispersing on food crops.
Unfortunately, ethylene gas in the form of a liquid is
most dangerous to humans who are applying the gas
to crops or in fruit or vegetable ripening rooms
because it can be very flammable and explosive. If a
person is contaminated by ethylene gas by
inhalation, it can cause dizziness, nausea, and even
suffocation or asphyxia (through lack of oxygen).
Gibberellic acid and ethylene are recommended for
grapes, pineapples, banana and other climacteric
fruits . Oxytocin is also used for fast growth and
ripening of fruits and vegetables, which has adverse
health impact on human body. Oxytocin is a birth
hormone showing uterotonic and galactogenic
activity which occurs naturally in animals, but when
it is injected into plant part such as stem, it functions
as growth promoter. It stimulates the plant hormones
such as cytokinin that invariably causes cell division
which results into biomass accumulation and hence
3
16
growth of fruits and vegetables . Adulteration in
food stuff has been regarded as a major social evil
and is a mind-boggling problem in society. The
implementation of prevention of food adulteration
Act and rules lies with the governments to keep a
vigil to check the use of hazardous chemicals for
ripening of fruits and vegetables.
Food Safety and Standard Authority of India
has advised to use gaseous ethylene for artificial
ripening of fruits (Table 2) . Ethylene is good but can
accelerate aging and eventual spoilage of many fruits
and vegetables. Therefore, it is advisable not to store
ethylene-sensitive fruits and vegetables together
with ethylene releasing fruits . If an ethylene-
sensitive fruit or vegetable is stored next to an
ethylene-producing fruit, ethylene can affect the
quality and reduce its shelf life. Some of ethylene-
sensitive vegetables are: broccoli, cabbage,
cauliflower, lettuce, .
In developing countries, strengthening of
public-private partnership is needed to introduce new
and modern postharvest technologies like
refrigerated transport vehicle, low temperature
storage and ethylene-induced ripening chamber. For
11
MAINTENANCE OF QUALITY AND SAFETY
IN SUPPLY CHAIN
Good practices
15
17
etc
Everyman’s Science Vol. L No. 6 February’16- March’16
Commodity Ethylene
concentration
(ppm)
Ethylene
exposure time
(hour)
Ripening
temperature o
( C)
Storage
temperature (oC)
Avocado 10-100 12-48 15-18 4.4-13
Banana 100-150 24 15-18 13-14
Honey dew melon 100-150 18-24 20-25 7-10
Kiwifruit -10 100 12-24 0-20 0.5-0
Mango -100 150 12-24 20-22 13-14
Orange degreening 1-10 24-72 20-22 5-9
Stone fruit 10-100 12-72 13-25 -0.5-0
Table-2: Ethylene concentration, optimum storage and ripening temperatures
for a few fruits are given below15
368
example, in the case of low temperature storage
facilities for fruits and some vegetables, the
government could start one or two in order to
encourage the private sectors to do more.
India lacks standardized quality assurance
systems for horticultural produce. Therefore, proper
arrangement should be made to develop national
quality management system to train, and ultimately
to accredit, growers and traders in the major
international certification such as HACCP, ISO,
GAP and GMP. Assistance can also be sought from
the Government of India who already have their own
standard quality management systems known as
IndoGAP.
Delivery of high quality and safe produce to
customers is the ultimate goal of efficient marketing.
There is public outcry on food safety due to
perceived health risk. Therefore, use of
recommended pesticides, plant growth regulators
and ripening agents must be ensured. Research,
training, motivation and strong media campaign are
necessary to improve the situation.
1. M. W. Siddiqui, R. S. Dhua, ,
, 1164-1168, 2010.
2. A. U. Rahman, F. R. Chowdhury, M. B. Alam,
, , 42-44, 2008.
3. Food and Agriculture Organization & Asian
Productivity Organization, Ed. R. S. Rolle,
Postharvest Management of Fruit and
Vegetables in the Asia-Pacific Region, 2006.
4. A. J. Dhembare,
, , 45-54, 2013.
Quality and grading standard
Safe use of chemicals
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