Biotechnology Advances 24 (2006) 389 – 409
www.elsevier.com/locate/biotechadv
Research review paper
The use of 1-methylcyclopropene (1-MCP) on fruits and vegetables
Chris B. Watkins ∗
Department of Horticulture, Cornell University, Ithaca, NY 14853, USA
Available online 10 March 2006
Abstract
The recent availability of the inhibitor of ethylene perception, 1-methylcyclopropene (1-MCP), has resulted in an explosion of
research on its effects on fruits and vegetables, both as a tool to further investigate the role of ethylene in ripening and senescence,
and as a commercial technology to improve maintenance of product quality. The commercialization of 1-MCP was followed by
rapid adoption by many apple industries around the world, and strengths and weaknesses of the new technology have been
identified. However, use of 1-MCP remains limited for other products, and therefore it is still necessary to speculate on its
commercial potential for most fruits and vegetables. In this review, the effects of 1-MCP on fruits and vegetables are considered
from two aspects. First, a selected number of fruit (apple, avocado, banana, pear, peaches and nectarines, plums and tomato) are
used to illustrate the range of responses to 1-MCP, and indicate possible benefits and limitations for commercialization of 1-MCPbased technology. Second, an outline of general physiological and biochemical responses of fruits and vegetables to the chemical
is provided to illustrate the potential for use of 1-MCP to better understand the role of ethylene in ripening and senescence
processes.
© 2006 Elsevier Inc. All rights reserved.
Keywords: Fruit; Vegetables; Ripening; Senescence; Ethylene; Softening; Respiration; Flavor; Antioxidants
Contents
1.
2.
Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Responses of selected fruit and vegetables to 1-MCP . . . . . . . . . . . .
2.1. Apple [Malus sylvestris (L.) Mill. var. domestica (Borkh.) Mansf.]
2.1.1. Ripening physiology and quality. . . . . . . . . . . . . .
2.1.2. Commercial application of 1-MCP. . . . . . . . . . . . .
2.2. Avocado. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
2.2.1. Ripening physiology and quality. . . . . . . . . . . . . .
2.2.2. Factors affecting commercial application of 1-MCP . . . . .
2.3. Banana (Musa sp., AAA group, Cavendish subgroup) . . . . . . . .
2.3.1. Ripening physiology and quality. . . . . . . . . . . . . .
2.3.2. Factors affecting commercial application of 1-MCP . . . . .
2.4. Pear (Pyrus communis L.). . . . . . . . . . . . . . . . . . . . . .
2.4.1. Ripening physiology and quality. . . . . . . . . . . . . .
2.4.2. Factors affecting commercial application of 1-MCP . . . . .
⁎ Tel.: +1 607 255 1784.
E-mail address: cbw3@cornell.edu.
0734-9750/$ - see front matter © 2006 Elsevier Inc. All rights reserved.
doi:10.1016/j.biotechadv.2006.01.005
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C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
2.5.
Peach and nectarine (Prunus persica L.) . . . . . . . . . . . . . . . . . . . .
2.5.1. Ripening physiology and quality . . . . . . . . . . . . . . . . . . . .
2.5.2. Factors affecting commercial application of 1-MCP . . . . . . . . . . .
2.6. Plum (Prunus domestica L. and Prunus salicina L.) . . . . . . . . . . . . . .
2.6.1. Ripening physiology and quality . . . . . . . . . . . . . . . . . . . .
2.6.2. Factors affecting commercial application of 1-MCP . . . . . . . . . . .
2.7. Tomato (Solanum esculentum Mill) . . . . . . . . . . . . . . . . . . . . . . .
2.7.1. Ripening physiology and quality . . . . . . . . . . . . . . . . . . . .
2.7.2. Factors affecting commercial application of 1-MCP . . . . . . . . . . .
3. Physiological and biochemical responses of fruits and vegetables to 1-MCP . . . . . .
3.1. Ethylene metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.2. Respiration rate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.3. Pigment metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.4. Cell wall metabolism . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.5. Volatile compound metabolism . . . . . . . . . . . . . . . . . . . . . . . . .
3.6. Nutritional quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7. Physiological storage disorders . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.1. Apple . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
3.7.2. Other fruits and vegetables . . . . . . . . . . . . . . . . . . . . . . .
3.7.3. A physiological basis for disorder development in response to 1-MCP
3.8. Pathological storage disorders . . . . . . . . . . . . . . . . . . . . . . . . . .
4. Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
1. Introduction
Ethylene is one of several plant growth regulators that
affect growth and developmental processes including
ripening and senescence (Abeles et al., 1992). It is a
simple hydrocarbon that can diffuse into and out of plant
tissues from both endogenous and exogenous (non-biological and biological) sources (Saltveit, 1999) and has
been the subject of extensive research on its biosynthesis
and action (Lelievre et al., 1998; Saltveit, 1999;
Giovannoni, 2001; Watkins, 2002; Adams-Phillips et
al., 2004).
Ethylene can profoundly affect quality of harvested
products. These effects can be beneficial or deleterious
depending on the product, its ripening stage, and its
desired use (Saltveit, 1999). Endogenous ethylene
production is an essential part of ripening of
climacteric fruit and probably acts as rheostat for
ethylene-dependent processes (Theologis, 1992). Exogenous ethylene application is routinely used to
initiate uniform ripening for fruit such as banana. Most
commonly, however, commercial strategies for horticultural products are based on avoiding exposure to
ethylene and/or attempting to minimize ethylene
production and action during ripening, harvest,
storage, transport and handling by temperature and
atmosphere control (Watkins, 2002). An exciting new
strategy for controlling ethylene production and thus
ripening and senescence of fruit, especially climacteric
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ones, as well as senescence of vegetative tissues, has
emerged with the discovery and commercialization of
the inhibitor of ethylene perception, 1-methylcyclopropene (1-MCP).
1-MCP is thought to interact with ethylene
receptors and thereby prevent ethylene-dependent
responses (Sisler and Blankenship, 1996; Sisler and
Serek, 1997, 2003). The use of cyclopropenes to
inhibit ethylene action was patented by Sisler and
Blankenship (1996). A commercial breakthrough in 1MCP application technology resulted from the formulation of 1-MCP as a stable powder in which it is
complexed with γ-cyclodextrin, so that 1-MCP is
easily released as a gas when the powder is dissolved
in water. 1-MCP was approved by the Environmental
Protection Agency (EPA) in 1999 for use on
ornamentals, and was marketed as EthylBloc® by
Floralife, Inc. (Walterboro, SC). AgroFresh, Inc., a
subsidiary of Rohm and Haas (Springhouse, PA),
subsequently developed 1-MCP under the trade name
SmartFresh™ and have global use rights for edible
horticultural products. 1-MCP has a non-toxic mode of
action, negligible residue and is active at very low
concentrations (E.P.A., 2002), and by 2005 food use
registration for the chemical had been obtained in
Argentina, Australia, Austria, Brazil, Canada, Chile,
Costa Rica, France, Guatemala and Honduras, Israel,
Mexico, the Netherlands, New Zealand, South Africa,
Switzerland, Turkey, UK, and the US. Registered
Table 1
Climacteric and non-climacteric fruit and vegetables for which responses to 1-MCP have been investigated from references available at Watkins and Miller (2005a)
Fruit (climacteric)
Banana (Musa L.)
Blueberry, highbush (Vaccinium
corymbosum L.)
Chinese bayberry (Myrica rubra
Siebold and Zuccarni)
Chinese jujube (Zizyphus jujube M.)
Custard apple (Annona squamosa L.)
Figs (Ficus carica L.)
Guava (Psidium guajava L.)
Kiwifruit (Actinidia deliciosa
(A. Chev) C.F. Liang et A.R.
Ferguson var. deliciosa
Lychee (Litchi chinensis)
Mamey sapote (Pouteria sapote
(Jacq.) H.E. Moore and Stearn)
Mango (Mangifera indica L.)
Vegetables
Melon (Cucumis melo L.)
Cherry (Prunus avium L.)
Broccoli (Brassica oleracea L.)
Mountain papaya (Vasconcellea pubescens)
Nectarine (Prunus persica Lindl.)
Clementine mandarin (Citrus reticulata L.)
Cucumber (Cucumis sativus L.)
Papaya (Carica papaya L.)
Peach (Prunus persica L. Batsch)
Grape (Vitis vinifera L.)
Grapefuit (Citrus paradisi Macf.)
Carrot (Daucus carota L.)
Chinese cabbage (Brassica campestris
L. spp. pekinensis (Lour) Olsson)
Chinese mustard (Brassica juncea var. foliosa)
Choysum (Brassica rapa var. parachinensis)
Pear (Pyrus communis L.)
Lime (Citrus latifolia Tanaka)
Chrysanthemum, garland (Chrysanthemum coronarium)
Pear (Pyrus pyrifolia Nakai)
Persimmon (Diospyros khaki L.)
Plum (Prunus salicina L.;
Prunus x domestica L.)
Tomato (Solanum esculentum Mill)
Orange (Citrus sinensis L. Osbeck)
Pepper (Capsicum frutescens L.)
Pineapple (Ananas comosus L.)
Coriander (Coriandrum sativum L.)
Lettuce (Lactuca sativa L.)
Mibuna (Brassica rapa var. nipposinica)
Strawberry (Fragaria × ananassa Duch.)
Watermelon (Citrullus lanatus)
Mizuna (Brassica rapa var. nipposinica)
Pak choy (Brassica rapa)
Parsley (Petroselinum crispum Mill.)
Potato (Solanum tuberosum)
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Apple [Malus sylvestris (L) Mill. var.
domestica (Borkh.) Mansf.]
Apricot (Prunus armeniaca L.)
Avocado (Persea americana Mill.)
Fruit (non-climacteric)
Tatsoi (Brassica rapa var. rosularis)
391
392
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
crops, which are specific to countries, include apple,
apricot, avocado, kiwifruit, mango, melon, nectarine,
papaya, peach, pear, pepper, persimmon, pineapple,
plantain, plum, squash, tomatoes and tulip bulbs.
Registration for use on various fruit and vegetables is
expected soon for other countries.
The impact of 1-MCP on postharvest science and
technology has been two-fold. First, it provides the
potential to maintain fruit and vegetable quality after
harvest. Second, 1-MCP provides a powerful tool to
gain insight into the fundamental processes that are
involved in ripening and senescence. A large literature on the responses of both whole and fresh cut
fruit and vegetables (as well as for ornamental
products) to 1-MCP is developing, with 40 papers
published in 2004 and 73 papers in 2003, compared
with 36 in 2002, 19 in 2000, and a total of 16 published
by 1998 (Watkins and Miller, 2005a). Recent reviews
on the effects of 1-MCP on horticultural products
include Blankenship and Dole (2003), Sisler and Serek
(2003), Watkins (2002), Watkins and Miller (2003),
Watkins and Ekman (2005) and Watkins and Miller
(2005b). A website bhttp://www.hort. cornell.edu/mcp/
N that categorizes the physiological and biochemical
responses for each product as decreased or delayed,
increased, or unaffected, was initiated in 2001 and is
regularly updated (Watkins and Miller, 2005a); research results are available for 35 fruit and 14 vegetables (Table 1).
In this review, the effect of 1-MCP on fruit and
vegetables is considered from two aspects. The first
considers the effects on factors that influence product
quality using several fruit that have received the most
attention in the literature, and that highlight some of
the challenges that exist in commercialization of 1MCP-based technology. While the responses of a wide
range of vegetables have been examined (Table 1);
most of these investigations have required supplementary treatment with exogenous ethylene to show effects
of 1-MCP and future commercial utilization is
uncertain. Therefore, individual vegetables are not
considered in detail here. Commercial development of
1-MCP has largely centered on apple fruit. While semicommercial trials have been carried out with a wide
variety of other registered crops, much of this work is
proprietary, and access to commercial information is
less easily obtained. The second aspect takes information from the literature to provide an overview about
the physiological and biochemical responses of fruit
and vegetables to 1-MCP to illustrate its potential to
better understand the role of ethylene in ripening and
senescence processes.
2. Responses of selected fruit and vegetables to 1-MCP
2.1. Apple [Malus sylvestris (L.) Mill. var. domestica
(Borkh.) Mansf.]
2.1.1. Ripening physiology and quality
1-MCP dramatically inhibits ripening of apple fruit.
The increases in ethylene production and internal ethylene concentrations (IECs) associated with the climacteric ripening stage are prevented or delayed by 1-MCP
treatment, the extent of inhibition being related to cultivar, storage type and length of storage (Fan et al.,
1999; Fan and Mattheis, 1999a; Rupasinghe et al., 2000;
Watkins et al., 2000; Dauny and Joyce, 2002; Jiang and
Joyce, 2002; Pre-Aymard et al., 2003; Saftner et al.,
2003; Defilippi et al., 2004; Arquiza et al., 2005; Bai et
al., 2005; Kondo et al., 2005; Mattheis et al., 2005;
Moran and McManus, 2005; Pechous et al., 2005;
Toivonen and Lu, 2005; Watkins and Nock, 2005).
Respiration rates in treated fruit have been less commonly reported but are also inhibited by 1-MCP (Fan et
al., 1999; Fan and Mattheis, 1999a, 2001; Jiang and
Joyce, 2002; Pre-Aymard et al., 2003; Saftner et al.,
2003; Defilippi et al., 2004; Mattheis et al., 2005;
Toivonen and Lu, 2005). However, respiration rates are
not reduced by 1-MCP below pre-climacteric levels (Mir
and Beaudry, 2002).
Softening is prevented or delayed by 1-MCP, the
effects of treatment often closely associated with ethylene production (Fan et al., 1999; Rupasinghe et al.,
2000; Watkins et al., 2000; Mir et al., 2001; Dauny and
Joyce, 2002; Pre-Aymard et al., 2003; Saftner et al.,
2003; Zanella, 2003; Defilippi et al., 2004; DeLong et
al., 2004; Jayanty et al., 2004; Bai et al., 2005;
Mattheis et al., 2005; Moran and McManus, 2005;
Toivonen and Lu, 2005). The components of texture
that are affected by 1-MCP have not been adequately
investigated but tissue toughness is greater in 1-MCPtreated fruit than untreated fruit (Baritelle et al., 2001).
Firmness retention can also be excellent in fruit kept at
high temperatures (20–24°C) after treatment (Fan et
al., 1999; Mir et al., 2001), and interestingly, Toivonen
and Lu (2005) found that effects of 1-MCP on an early
ripening summer apple cultivar were lost at storage
temperatures below 15 °C.
Loss of greenness of the background or ground color
of the fruit skin, usually considered as a negative attribute in commercial conditions, is inhibited (Fan and
Mattheis, 1999a, 2001; Dauny and Joyce, 2002; Jiang
and Joyce, 2002; Pre-Aymard et al., 2003; Saftner et al.,
2003; Zanella, 2003), although no effect of 1-MCP on
color was detected by Dauny and Joyce (2002).
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
In general, 1-MCP delays loss of titratable acidity
(TA) concentrations (Fan et al., 1999; Fan and Mattheis,
1999a, 2001; Watkins et al., 2000; Pre-Aymard et al.,
2003, 2005; Saftner et al., 2003; Zanella, 2003;
Defilippi et al., 2004; Bai et al., 2005; Toivonen and
Lu, 2005). However, absence of treatment effects (Mir
et al., 2001) or mixed responses depending on storage
type (air or CA), on TA have been reported (Watkins et
al., 2000).
Soluble solid concentrations (SSC) in 1-MCP treated
fruit can be higher, lower or the same as those in untreated fruit (Fan et al., 1999; Watkins et al., 2000; Dauny
and Joyce, 2002; DeEll et al., 2002; Saftner et al., 2003;
Zanella, 2003; Bai et al., 2005; Moran and McManus,
2005; Pre-Aymard et al., 2005).
Total volatile contents are reduced by 1-MCP treatment, although individual volatiles are affected differentially (Rupasinghe et al., 2000; Lurie et al., 2002;
Saftner et al., 2003; Defilippi et al., 2004; Bai et al.,
2005; Kondo et al., 2005). These effects are discussed in
detail in Section 3.5.
Apples are susceptible to a wide variety of physiological and pathological disorders, and the impact of
1-MCP on susceptibility of fruit to these disorders is
discussed in Sections 3.7 and 3.8.
Little formal sensory research is available on the
effects of 1-MCP on consumer acceptance of apples,
partly because recent registration has precluded consumer testing. The rapidly ripening summer apple
‘Anna’ treated with 1-MCP that had less fruity, ripe
and overall aromas, and were firmer, crisper, juicier and
less mealy, were more preferred in sensory analyses than
untreated fruit (Lurie et al., 2002; Pre-Aymard et al.,
2005).
2.1.2. Commercial application of 1-MCP
The apple fruit provides an important example of a
horticultural product to illustrate the opportunities and
limitations of 1-MCP-based technologies. The apple
was the first crop that received registration for 1-MCP
use, and 1-MCP use has been incorporated rapidly by
industries around the world. The feature of 1-MCP
technology that has made it widely accepted by apple
industries is that treated apple fruit maintain texture
after removal from storage; in contrast, while CA
storage can also maintain quality of apples during
storage, these benefits are often lost during the
subsequent shipping and marketing periods resulting
in overly ripe and soft apple at the retail level.
Nevertheless, the rapid commercial adoption of 1MCP has not surprisingly resulted in a number of
challenges to growers and storage operators. The
393
“apple” is a fruit with a wide variety of cultivars
with different ripening rates and susceptibility to
various physiological and pathological disorders, and
depending on cultivar, may be stored for up to a
year from harvest (Watkins, 2003). Also, preferences
for fruit attributes in the marketplace vary greatly
with cultivar, and include those with firm and acid
characteristics as well as those that are soft and
aromatic. 1-MCP-treated fruit have to meet varietal
requirements.
The research described in Section 2.1.1 has catalogued a wide variety of apple fruit responses to 1MCP, but many of these results have been obtained
under ideal laboratory conditions, often when fruit are
treated on the day of harvest. Under commercial
conditions fruit are usually placed into cold storage
and may be accumulated over several days before
treatment with 1-MCP. Research that examines the
effects of various harvest and handling procedures is
emerging in the literature, and is resulting in
development of protocols to ensure that maximum
benefits of the technology are realized by the industry.
The relationship between 1-MCP concentration and
storage period is affected by cultivar and storage type
(Rupasinghe et al., 2000; Watkins et al., 2000; PreAymard et al., 2003). Longer exposure periods are
required as the treatment temperature decreases (DeEll
et al., 2002), although little difference in responses of
fruit treated with 1-MCP for 24h on the day of harvest
at 20 °C or after cooling overnight were detected
(Dauny and Joyce, 2002; Watkins and Nock, 2005). In
addition, 1-MCP may lead to modification of CA
recommendations, for example, it may reduce the
requirement for CO2 during storage to maintain
firmness (DeEll et al., 2005).
Ethylene production by apple fruit occurs both on
and off the tree when the climacteric is initiated, and
therefore the effectiveness of 1-MCP is affected both
by the maturity/ripening stage at harvest and by the
period of time that the fruit are kept in cold storage
before treatment. These two factors are inter-related as
more mature fruit at harvest produce autocatalytic
ethylene sooner than earlier harvested fruit. Cultivar
effects are also important; Mir et al. (2001) found
relatively small effects of harvest maturity for ‘Delicious’, but large effects were shown for ‘Empire’
(Watkins and Nock, 2005). Higher 1-MCP concentrations result in better responses in fruit of advanced
maturity (Watkins, unpublished data). However, these
may exceed the maximum treatment concentrations of
1-MCP, which are established by regulation for each
country, for example, 1μl l− 1 for apples in the US.
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C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Watkins and Nock (2005) found that the effect of
delays between harvest and application of 1-MCP is
affected by cultivar, storage type and storage length. The
suppliers of the commercial product, SmartFresh™,
provide recommendations for maximum delays between
harvest and treatment, but these times are variable depending on fruit physiological condition, and a rule of
thumb is that the delay times must be as short as possible
if longer storage periods are desired by the storage
operator. It may be possible to store treated fruit at
warmer than normal cold storage temperatures if decay
and loss of other quality attributes such as TA is not
unacceptably high (Mir et al., 2001; Jayanty et al.,
2004).
CA can prolong the impact of 1-MCP on both
physical and sensory responses of apple fruit (Rupasinghe et al., 2000; Watkins et al., 2000; Mattheis et al.,
2005). It is possible that 1-MCP can be an alternative to
CA storage, but the two technologies generally are
more effective when used in combination (Rupasinghe
et al., 2000; Watkins et al., 2000). Importantly,
variation in response of different fruit lots to 1-MCP
can occur under commercial conditions, and CA use as
a supplement can become more critical. Fruit from
orchard lots within a room that do not respond to 1MCP continue to deteriorate as storage times increase
resulting in unacceptable commercial losses (Watkins,
unpublished data). Nevertheless, 1-MCP may be an
excellent replacement for CA storage for short term air
storage, especially for maintaining quality of summer
apples (Toivonen and Lu, 2005) and of other cultivars
that deteriorate after only 2–3 months of storage
(Watkins et al., 2000; Bai et al., 2005), especially for
smaller local market operations that do not have CA
facilities.
The availability of 1-MCP for the apple is allowing
the rapid identification of commercial opportunities and
limitations of the technology. The success of 1-MCP for
apple fruit appears to be based greatly on the maintenance of texture, especially because apple, unlike
many other fruit types, do not soften markedly after
harvest, and to date, at least the minimum demands for
flavor have been met for most treated cultivars. An
extensive literature describing many aspects of the responses of apple fruit can be expected in the next several
years.
2.2. Avocado
2.2.1. Ripening physiology and quality
Ripening of avocado fruit is not initiated until they are
harvested, and the fruit then softens to an edible texture
and with skin color changes appropriate to the cultivar.
Fruit responses to 1-MCP are ‘concentration × exposure
time’-dependent in most (Feng et al., 2000; Jeong et al.,
2002), but not all (Woolf et al., 2005), studies. Both the
timing of the peak of ethylene production and the
respiratory climacteric are delayed (Feng et al., 2000,
2004; Jeong et al., 2002, 2003; Hershkovitz et al., 2005).
Maximum rates of ethylene and carbon dioxide were
usually lower, but the magnitude can be higher in some
cultivars (Jeong et al., 2003; Hershkovitz et al., 2005).
Treated fruit are firmer, slower to soften, and slower
to change skin color (Feng et al., 2000, 2004; Hofman et
al., 2001; Jeong et al., 2002; Adkins et al., 2005;
Hershkovitz et al., 2005; Woolf et al., 2005). 1-MCP
treated fruit have lower weight loss than untreated fruit
(Jeong et al., 2002). 1-MCP treatment combined with
waxing does not extend the shelf life more than 1-MCP
alone, but results in reduced weight loss and better
maintenance of green color (Jeong et al., 2003).
2.2.2. Factors affecting commercial application of 1-MCP
Successful commercial utilization of 1-MCP for
avocado is dependent on an appropriate balance
between excessively delayed ripening that can increase
decay development, especially after removal from
storage, and desirable increases in storage potential
with reduced internal disorders (Woolf et al., 2005).
Adkins et al. (2005) concluded that 1-MCP could extend
marketing periods, but that treated fruit must have low
disease inoculum load or be more resistant to infection
to avoid increased decay potential.
Diffuse flesh discoloration, a symptom of internal
chilling injury, was reduced in 1-MCP-treated fruit,
although external chilling injury (skin blackening) in
‘Hass’ was not affected by treatment (Pesis et al., 2002;
Woolf et al., 2005). Therefore, 1-MCP could allow
storage of fruit at lower temperatures.
1-MCP delayed ripening after ethylene treatment if
fruit softening was not initiated (Jeong and Huber,
2004). Ethylene treatment could overcome inhibition of
ripening by 1-MCP at lower treatment concentrations,
but ethylene recovery of 1-MCP ripening inhibition was
only partial and differed by ripening factor (Jeong and
Huber, 2004).
2.3. Banana (Musa sp., AAA group, Cavendish subgroup)
2.3.1. Ripening physiology and quality
The banana fruit are typically harvested at the mature
green stage of maturity, transported, and then ripened
artificially with ethylene before being sent to market.
Banana had increased ‘green life’ when treated with
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
1-MCP, responses being ‘concentration × exposure time’
dependent (Jiang et al., 1999b; Harris et al., 2000;
Bagnato et al., 2003). Ethylene production and respiration rates were lower in 1-MCP-treated fruit than in
untreated fruit (Golding et al., 1998, 1999; Pathak et al.,
2003; Pelayo et al., 2003; Lohani et al., 2004). Softening
of fruit was inhibited by 1-MCP treatment (Jiang et al.,
1999a,b; Macnish et al., 2000; Botrel et al., 2002;
Pelayo et al., 2003; Lohani et al., 2004). Color changes
were also delayed in 1-MCP treated fruit (Botrel et al.,
2002), and may have been associated with disrupted or
incomplete and uneven yellowing, even in the presence
of propylene (Golding et al., 1998; Harris et al., 2000;
Macnish et al., 2000). Total volatile production of fruit
was inhibited by 1-MCP treatment, and quantitatively,
ester concentrations were lower, while those of alcohols
were higher, in treated fruit (Golding et al., 1998). Little
is known about the effect of 1-MCP on other
compositional changes of banana fruit, although sugar
content was not affected by treatment (Golding et al.,
1998).
2.3.2. Factors affecting commercial application of 1-MCP
The limitation for commercial application of 1-MCP
for bananas may be the partial disruption of ripening
events in treated fruit (Golding et al., 1998) that
highlight the integrative role of ethylene in ripening
(Golding et al., 1999). Harris et al. (2000) concluded
that 1-MCP had limited commercial potential because
of the uneven color development, and that this problem
was exacerbated because of the range of maturities
present in a commercial consignment. In contrast,
however, Bagnato et al. (2003) found that while
ripening was inhibited and decay increased at high 1MCP concentrations, a lower concentration of 300nl
l− 1 resulted in delayed ripening but firmness, color,
SSC and aroma profiles were similar with those of
untreated fruit when compared at the same ripening
stages.
One strategy for use of 1-MCP on fruit such as
banana for which ripening is artificially initiated with
ethylene treatment could be to apply 1-MCP after this
treatment. Pelayo et al. (2003) concluded, however,
that variability in responses of partially ripe bananas
was too variable for commercial application. Also, if
1-MCP was applied to fruit 24 h after propylene
treatment to induce ripening, then the onset of
ethylene and respiration rates was not affected but
color and volatile production was inhibited (Golding
et al., 1998). Treatment of pre-climacteric fruit, or
earlier 1-MCP treatment, resulted in inhibition of all
processes.
395
2.4. Pear (Pyrus communis L.)
2.4.1. Ripening physiology and quality
The effects of 1-MCP have been investigated using
summer, autumn and winter pears. High quality pear
fruit have a buttery texture, with color change appropriate to the cultivar, and development of characteristic taste
and aroma associated with sugar and acid contents and
volatile production (Kappel et al., 1995; Ma et al., 2000).
Pears require exposure to chilling temperatures to ripen
properly, with winter pears requiring as long as 8 weeks.
Ethylene production was inhibited by 1-MCP treatment
(Argenta et al., 2003; Hiwasa et al., 2003; Kubo et al.,
2003; Ekman et al., 2004; Larrigaudiere et al., 2004;
Trinchero et al., 2004; Mwaniki et al., 2005). Respiration
rates were also lower in 1-MCP-treated fruit (Argenta et
al., 2003; Kubo et al., 2003; Ekman et al., 2004).
1-MCP delayed or prevented fruit softening, the
degree of response depending on the cultivar and
1-MCP concentration applied (Baritelle et al., 2001;
Argenta et al., 2003; Hiwasa et al., 2003; Kubo et al.,
2003; Calvo and Sozzi, 2004; Ekman et al., 2004;
Trinchero et al., 2004). Loss of greenness or yellowing
but not SSC, was inhibited by 1-MCP (Calvo and Sozzi,
2004; Larrigaudiere et al., 2004; Trinchero et al., 2004).
Treated fruit had higher TA in one study (Argenta et al.,
2003) but no effect of 1-MCP was found by others
(Calvo and Sozzi, 2004; Larrigaudiere et al., 2004;
Trinchero et al., 2004).
2.4.2. Factors affecting commercial application of 1-MCP
‘1-MCP concentration × time’ relationships for delays
of ripening have been shown (Argenta et al., 2003), and
the 1-MCP concentrations that delay, but do not
ultimately prevent, normal ripening are variable. Application of 0.2 μl l− 1 1-MCP resulted in normal ripening
with reduction in over-ripening problems (Calvo and
Sozzi, 2004), while concentrations as high as 10 and
100 μl l− 1 to fruit in which ripening was initiated by
chilling temperatures resulted in maintenance of optimal
eating firmness for extended periods and prevention of
senescent breakdown development after storage (Kubo
et al., 2003).
Repeated 1-MCP applications can further slow down
ripening (Ekman et al., 2004), but sensitivity to second
applications are affected if ethylene production by fruit
has been initiated during storage (Trinchero et al., 2004).
The efficacy of post-storage ethylene treatments to initiate ripening of 1-MCP-treated fruit after storage
depends on 1-MCP concentration and storage duration
(Argenta et al., 2003; Calvo and Sozzi, 2004; Ekman et
al., 2004).
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C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Both positive and negative aspects of 1-MCP that
may be commercially important for pear fruit have been
identified. 1-MCP reduces susceptibility of fruit to skin
browning, and vibration and impact bruising, and therefore its use may permit greater flexibility during grading,
packaging and transport operations (Calvo and Sozzi,
2004; Ekman et al., 2004). However, increased storage
periods of 1-MCP-treated fruit may result in greater
weight loss (Calvo and Sozzi, 2004). Ethylene appears to
be required for both initiation and progression of ripening of pears (Hiwasa et al., 2003). Ekman et al. (2004)
found that skin color and firmness was dissociated and
suggested that this could problematic at the retail level.
Variation of individual fruit treated with 1-MCP could
result in the need for post-treatment sorting of fruit
(Trinchero et al., 2004).
2.5. Peach and nectarine (Prunus persica L.)
2.5.1. Ripening physiology and quality
Ethylene production is inhibited by 1-MCP treatment of peaches and nectarines (Mathooko et al.,
2001; Fan et al., 2002; Rasori et al., 2002; Liguori et
al., 2004; Bregoli et al., 2005; Girardi et al., 2005),
although transient increases in production were
detected immediately after treatment in one study
(Fan et al., 2002). Ethylene production of 1-MCP
treated fruit was unaffected at the time of treatment,
but was reduced after storage (Dong et al., 2001b).
Recovery from 1-MCP-induced ripening inhibition
resulted in greater production of ethylene than
observed in untreated fruit (Rasori et al., 2002).
Respiration rates of treated fruit were lower (Fan et
al., 2002), or not affected (Dong et al., 2001b; Liguori
et al., 2004) by 1-MCP treatment. Softening of fruit
was delayed when fruit were kept at about 20 °C
(Dong et al., 2001b; Mathooko et al., 2001; Fan et al.,
2002; Rasori et al., 2002; Bregoli et al., 2005; Liu et
al., 2005), and in fruit from early and late harvest
(Liguori et al., 2004). However, Fan et al. (2002)
found that the effects of fruit maturity were greater
than those of 1-MCP treatment, with early harvested
fruit showing little response to treatment. Also,
beneficial effects of 1-MCP were lost at 4°C (Bregoli
et al., 2005).
1-MCP treatment either did not affect SSC of fruit
(Liguori et al., 2004), resulted in lower SSC (Fan et al.,
2002; Bregoli et al., 2005), or the increase of SSC
during ripening was delayed (Liu et al., 2005). Loss of
TA was reduced in high acid (Fan et al., 2002; Liguori et
al., 2004; Bregoli et al., 2005; Liu et al., 2005), but not
in low acid cultivars (Liguori et al., 2004).
2.5.2. Factors affecting commercial application of 1-MCP
Responses of fruit to 1-MCP are affected by
concentration and exposure period, but not treatment
temperature (Liguori et al., 2004). Optimal 1-MCP
concentrations vary greatly from as low as 0.4μl l− 1
(Liu et al., 2005) to 5 μl l− 1 (Liguori et al., 2004), the
latter concentration being higher than that registered for
use. Inhibition of fruit ripening is transitory in all
published studies, but repeated 1-MCP applications
helps maintain suppression of ripening (Liu et al., 2005).
The transitory effect of 1-MCP is not related to diffusion
limitations within the flesh (Hayama et al., 2005). 1MCP treatment at ambient temperatures could allow
commercially significant extension of fruit shelf life.
However, decreased 1-MCP effects in fruit stored at 4
o
C (Bregoli et al., 2005), and a greater incidence of
chilling-related disorders in treated fruit (Dong et al.,
2001b; Fan et al., 2002; Girardi et al., 2005) suggests
that this technology is limited for extending the storage
life of peaches and nectarines in cold storage.
2.6. Plum (Prunus domestica L. and Prunus salicina L.)
2.6.1. Ripening physiology and quality
1-MCP prevented or delayed the climacteric increase
in ethylene production of plums (Abdi et al., 1998;
Dong et al., 2001a, 2002; Martinez-Romero et al., 2003;
Salvador et al., 2003; Valero et al., 2003, 2004), even
when fruit were harvested close to the climacteric peak
(Salvador et al., 2003). Respiration rates were also decreased or the climacteric increase delayed (Dong et al.,
2002; Martinez-Romero et al., 2003; Salvador et al.,
2003; Valero et al., 2003), but no effect of 1-MCP
treatment was detected by Dong et al. (2001a).
Softening of the fruit was delayed by 1-MCP treatment
(Dong et al., 2001a, 2002; Skog et al., 2001; MartinezRomero et al., 2003; Salvador et al., 2003; Valero et al.,
2003, 2004; Menniti et al., 2004). Skin color changes
were delayed by 1-MCP (Dong et al., 2002; MartinezRomero et al., 2003; Salvador et al., 2003; Valero et al.,
2003, 2004; Menniti et al., 2004), and weight loss
during and after storage decreased (Martinez-Romero et
al., 2003; Valero et al., 2003).
Responses of SSC and TA to 1-MCP treatment are
variable. The SSC was not affected by 1-MCP treatment
(Dong et al., 2002; Salvador et al., 2003; Menniti et al.,
2004), but its ripening-associated increase was (Valero et
al., 2004). While TAwas not affected by 1-MCP treatment
(Menniti et al., 2004), loss of acidity was reduced in other
studies (Dong et al., 2002; Salvador et al., 2003). The SSC
to TA ratio was lower in 1-MCP-treated than untreated
fruit (Martinez-Romero et al., 2003; Valero et al., 2003).
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Although plums are categorized as climacteric fruit,
suppressed-climacteric cultivars are available (Abdi et
al., 1998; Martinez-Romero et al., 2003). The ‘suppressed’ cultivars did not ripen when treated with 1MCP unless they were subsequently treated with
propylene (Abdi et al., 1998), and the effects of 1MCP were not dose dependent, maximum responses
occurring at the lowest 1-MCP concentration applied
(Martinez-Romero et al., 2003). In contrast, dose
dependent responses were shown for a normal ethylene-producing cultivar.
2.6.2. Factors affecting commercial application of 1-MCP
Postharvest softening and susceptibility to mechanical injury and pathogens are major factors limiting the
shipping, storage and shelf life of plums. The degree
of response to 1-MCP varies greatly by cultivar and
harvest maturity (Abdi et al., 1998; Skog et al., 2001;
Martinez-Romero et al., 2003) but reports of extension
of storage periods from 1 week for untreated fruit to 4
weeks for 1-MCP-treated fruit plus 7 days at 20°C
without negative effects indicate that 1-MCP may be a
very useful technology for this fruit. Moreover, 1MCP is effective at later stages of maturity when
better quality characteristics have developed (Salvador
et al., 2003; Valero et al., 2003). Studies on
climacteric and suppressed-climacteric cultivars indicate however, that 1-MCP concentrations will need to
be calibrated for cultivars with different ethylene
production (Abdi et al., 1998; Martinez-Romero et al.,
2003).
No differences were noted between treatment at 0 and
20 °C (Menniti et al., 2004), although Valero et al. (2003)
suggested that treatment at cold storage temperatures
resulted in better control of ethylene. 1-MCP treatment
prior to simulated mechanical harvest decreased fruit
losses due to bruising (Lippert and Blanke, 2004). In one
of the few studies that have investigated possible interactions between 1-MCP treatment and postharvest
handling operations, Valero et al. (2004) found that
1-MCP treatment of fruit packed in small ventilated
cardboard boxes resulted in better ripening control than
for bulked fruit.
2.7. Tomato (Solanum esculentum Mill)
2.7.1. Ripening physiology and quality
1-MCP treatments markedly affected ripening of
tomato fruit by inhibiting ethylene production (Hoeberichts et al., 2002; Wills and Ku, 2002; Krammes et
al., 2003; Opiyo and Ying, 2005; Tassoni et al., in
press). Other ripening processes that are inhibited
397
include respiration rates (Wills and Ku, 2002; Colelli et
al., 2003; Krammes et al., 2003), color change and
softening (Sisler et al., 1996; Hoeberichts et al., 2002;
Colelli et al., 2003; Mostofi et al., 2003; Mir et al.,
2004; Opiyo and Ying, 2005; Tassoni et al., in press).
TA was higher in treated fruit (Moretti et al., 2002;
Wills and Ku, 2002; Krammes et al., 2003; Opiyo and
Ying, 2005), but SSC were not affected by 1-MCP
treatment (Moretti et al., 2002; Wills and Ku, 2002;
Colelli et al., 2003; Krammes et al., 2003; Mir et al.,
2004; Opiyo and Ying, 2005). Weight loss from fruit
was not affected by 1-MCP treatment (Wills and Ku,
2002; Colelli et al., 2003). Only small effects of
treatment on aroma volatiles were detected by Mir et al.
(2004), although changes tended towards those volatiles that were associated with harvest of fruit at earlier
ripening stages.
2.7.2. Factors affecting commercial application of 1-MCP
The desirable response of fresh market tomato fruit
to 1-MCP is a delay of ripening, but then ripening to
redness, desired softness, and flavor development.
Another possible commercial benefit of 1-MCP is
inhibition of abscission of cherry tomatoes from vines
(Beno-Moualem et al., 2004). The extent of ripening
inhibition of tomato fruit is affected by 1-MCP concentration, exposure time and ripening stage (Sisler et
al., 1996; Hoeberichts et al., 2002; Moretti et al., 2002;
Wills and Ku, 2002; Mir et al., 2004; Opiyo and Ying,
2005), and optimal treatment concentrations are also
affected by cultivar (Krammes et al., 2003). Fruit
recover capacity to ripen after treatment, but second
applications further delay ripening (Hoeberichts et al.,
2002; Mir et al., 2004). However, the maturity stage of
the fruit at the time of 1-MCP treatment affects the
ability of the fruit to recover; mature green and breaker
stage fruit shriveled and developed decay before
ripening, although fruit treated at pink and light red
stages ripened properly after a delay (Hurr et al.,
2005). The presence of ethylene was required
throughout for ripening even when 1-MCP was
applied at advanced ripening stages (Hoeberichts et
al., 2002). Mostofi et al. (2003) also found that
treatment of mature green fruit resulted in impaired
color development, and that the ripening temperature
was important; whereas ripening of fruit treated at the
breaker stage was coordinated at 15, 20 and 25 °C,
development of color was out of phase with softening
at 25°C. The reddening of locular tissues was later
than that of pericarp tissues after treatment of mature
green fruit, which could affect appearance of fresh cut
slices (Mir et al., 2004).
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C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Formal sensory studies on the effects of 1-MCP on
consumer acceptability are not available. However, Wills
and Ku (2002) concluded that MCP-treated fruit should
be of superior quality because of improved SSC / TA
ratios. 1-MCP had little effect on aroma volatiles in the
study of Mir et al., (2004), but negatively and
irreversibly affected them in informal sensory analyses
reported by Hurr et al. (2005).
3. Physiological and biochemical responses of fruits
and vegetables to 1-MCP
Generalizations regarding the effects of 1-MCP on
physiological and biochemical responses of fruits and
vegetables are shown in Table 2. Specific examples are
provided here, but fuller documentation of these effects
is described on a website bhttp://www.hort. cornell.edu/
mcp/N (Watkins and Miller, 2005a).
3.1. Ethylene metabolism
The action of 1-MCP is mediated through the
inhibition of ethylene perception of plant tissues by
interacting with the receptor and competing with
ethylene for binding sites (Sisler et al., 1996; Sisler and
Serek, 1997, 2003). Therefore, the effectiveness of
inhibition of ripening and/or senescence of fruit and
vegetables is a function of the 1-MCP concentration
applied, up to saturation of the binding sites. Depending
on the product it can be desirable for the inhibition of
ethylene-mediated responses to persist indefinitely, especially in the case of leafy vegetables, but for fruit,
recovery from 1-MCP-induced inhibition of ripening is
often essential in order to provide a ripened product that
is acceptable to the consumer.
The extent and longevity of 1-MCP action is affected
by species, cultivar, tissue and mode of ethylene biosynthesis induction. A ‘concentration × time’ effect is
apparent with longer exposure periods required for lower
1-MCP concentrations to obtain the same physiological
effects (Sisler and Serek, 1997). Some products such as
pea require higher concentrations (40 nl l − 1 ) than
carnations (0.5 nl l− 1) and banana (0.7 nl l− 1), suggesting
that new receptors are produced in growing tissues or
that a low affinity form of the receptors is present (Sisler
and Serek, 2003). Synthesis of new binding sites may be
affected by temperature; in banana, temperatures between 30 and 40°C results in faster recovery of ripening,
while application of 1-MCP at 2.5 °C is less effective
than at 15 and 20 °C suggesting that binding of 1-MCP at
low temperatures was incomplete (Jiang et al., 2002b,
2004c).
Research with yeast has shown that ETR1 and ERS1,
genes encoding the ethylene binding proteins, show equal
sensitivity to 1-MCP (Hall et al., 2000), but little research
on expression of these genes in fruit and vegetables is yet
available. Accumulation of transcripts for the genes
encoding ERS decreased in treated apple (Defilippi et al.,
2005). Rasori et al. (2002) found that 1-MCP did not
affect transcription of the gene PP-ETR1, but downregulated that of PP-ERS1. Recovery from 1-MCP
inhibition was associated with increased accumulation
of PP-ERS1 transcripts. In tomato, recovery from
ripening inhibition was associated with increased gene
expression for both ETR1 and ERS1 (Tassoni et al., in
press).
Ethylene production of fruit is usually inhibited by
1-MCP treatment, but the persistence of the inhibition
can be variable (Fan et al., 1999; Fan and Mattheis,
1999a; Dong et al., 2002; Jeong et al., 2002; Ergun et al.,
2005). Ethylene production is not always inhibited. The
decline in ethylene production was slower over time in
1-MCP treated pineapples than untreated fruit (Selvarajah et al., 2001), and greater ethylene production has
been observed in fruit and vegetables depending on
cultivar, maturity, stage or ripening or 1-MCP concentration, including treated avocado (Jeong et al., 2003;
Hershkovitz et al., 2005), banana (Golding et al., 1998),
grapefruit (Mullins et al., 2000), strawberry (Tian et al.,
2000), Chinese cabbage (Porter et al., 2005), coriander
(Jiang et al., 2002a), and parsley (Ella et al., 2003). In
some cases the increased ethylene does not appear to
affect other senescence processes, e.g., 1-MCP citrus
fruit remained green despite higher ethylene production
(Mullins et al., 2000), but increased ethylene production
can accelerate senescence in other tissues, e.g., parsley
(Ella et al., 2003). It is likely that stimulated ethylene
production is due to loss of negative feedback regulation
of ethylene biosynthesis.
The genes encoding two key enzymes of the ethylene
biosynthetic pathway, 1-aminocyclopropane carboxylic
acid oxidase (ACO) and 1-aminocyclopropane carboxylic
acid synthase (ACS), and their respective enzyme activities have been studied in several crops. In apple, banana,
melon and pear fruit, inhibition of ethylene production by
1-MCP was accompanied by lower expression of these
genes (Lelievre et al., 1997; de Wild et al., 1999; Defilippi
et al., 2005), and lower activities of ACS and ACO (Dong
et al., 2001b; Pathak et al., 2003; Defilippi et al., 2005). In
peach, inhibited ethylene production was associated with
reduced activity of ACO and a reduction in PP-ACO1 and
PP-ACO2 transcript accumulation, but 1-aminocyclopropane carboxylic acid (ACC) accumulated in treated fruit,
and PP-ACS1 expression and ACS activity was not
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C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Table 2
Generalizations regarding the effects of 1-MCP on metabolism of fruit and vegetables
Attribute or process affected Enzyme activity or associated gene
expression
Increased (↑), decreased (↓), or
unchanged (↔)
Ethylene metabolism
Ethylene perception
Ethylene production
↓↔
↓↑
ACC synthase (ACS) expression and ↓
activity
ACC oxidase (ACO) expression and ↓
activity
ETR1, ERS1
Respiratory metabolism
Pigments
Respiration rate
SSC
TA
Chlorophyll degradation
Lycopene accumulation
Anthocyanin accumulation
Chlorophyllase activity
↓ ↑↔
↓ ↑↔
↓ ↑↔
↓
↓
↓
↓
Phenolic metabolism
Total phenolic content
↓
Phenylalanine ammonia lyase (PAL) ↓
activity
Polyphenol oxidase (PPO) activity
↓
Cell wall metabolism
Soluble polyuronide content
Polygalacturonase (PG) activity
Pectin methylesterase (PME)
Endo-β-1,4-glucanase (EGase)
Glycosidases
↓
↓
↓
↓
↓↔
Volatile compound metabolism
↓
↔
↔
↓↑
Esters
Aldehydes
Terpenoid biosynthesis
Acetaldehyde and ethanol
accumulation
Alcohol acyl transferase activity
Alcohol dehydrogenase activity
Nutritional
Vitamin C loss
Anthocyanin contents
Phenolic contents
Antioxidant activity
loss
↓
↔
↓
↓
↓↔
↓
Physiological disorders
Senescent disorders
Chilling injury
Superficial scald (apples and
pears)
Ethylene-induced disorders
Controlled atmosphereinduced
Abscission
↓
↓↑
↓
Susceptibility to pathogens
Fungal growth
↑↓↔
↓↔
↓
↑
↓
Pathological disorders
affected by treatment (Mathooko et al., 2001). 1-MCP
treated nectarines had lower ACS, ACO1 and ACO2
transcript accumulations than untreated fruit at ambient
but not cold storage temperatures (Bregoli et al., 2005).
Application of 1-MCP to avocados at the pre-climacteric
stage and at the onset of the climacteric inhibited ACS and
ACO activities, and the transcription of PA-ACS1, and
suppressed PA-ACO and PA-ERS1 mRNAs to trace
400
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levels (Owino et al., 2002). Discontinuation of 1-MCP
action resulted in super-induction of these genes in the
fruit. In citrus, 1-MCP-induced increases of ethylene
production were associated with greater ACC accumulation and higher ACS transcript accumulation and enzyme
activity (Mullins et al., 2000).
In tomato, transcript accumulations of ACO1, phytoene synthase 1 (PSY1) and expansin 1 (EXP1), used as
indicators of treatment effects on ethylene biosynthesis,
color and softening, respectively, were decreased by
1-MCP (Hoeberichts et al., 2002). Increases in transcript
abundance of LE-ACS2, LE-ACS4 and LE-ACO1
mRNAs in ripening fruit were inhibited by 1-MCP, but
ethylene production, ACC content and ACS and ACO
activities were not inhibited to the expected levels suggesting involvement of negatively regulated genes in
ethylene biosynthesis (Nakatsuka et al., 1997). Reduced
ethylene production of fruit that were treated at the turning
and pink stages was accompanied by inhibited ACS2,
ACS4, ACO1 and ACO4 transcript accumulation, while
several other ACS genes were not affected (Nakatsuka et
al., 1998). 1-MCP abolished expression of E4 mRNA in
wounded tomato fruit, but not expression profiles of LEACS2, LE-ACS6 and LE-ACO1 (Yokotani et al., 2004).
Itai et al. (2003) showed that α-L-arabinofuranosidase
(LeARF1) expression was negatively regulated by ethylene, while two B-D-xylosidase genes were independent
of ethylene action. NR transcripts were immediately
suppressed by 1-MCP treatment but as fruit ripened, they
recovered from 1-MCP in a similar pattern to that of the
ACS and ACO genes (Tassoni et al., in press).
3.2. Respiration rate
As described for several fruit in Section 2, the
respiration rates of most treated products decreased or
were delayed, especially in climacteric fruit where increases accompany increases of ethylene production.
The peak respiration rates at the climacteric were reduced by 1-MCP (Jeong et al., 2002, 2003). Enhanced
respiration rates of ethylene-treated strawberry fruit
were reduced by 1-MCP at earlier harvests, but not in
fruit from later harvests (Tian et al., 2000). Bower et al.
(2003) found higher respiration rates in 1-MCP-treated
strawberry fruit that may have been associated with
earlier onset of decay.
Starch degradation is sometimes delayed in 1-MCPtreated fruit (Fan et al., 1999). SSC in treated products
might be expected to be higher than in untreated
products because of lower respiration rates, but can be
higher, lower or the same as in untreated fruit depending
on the product and the storage conditions (Fan et al.,
1999; Watkins et al., 2000; Benassi et al., 2003). The
sugar content of banana was not affected by 1-MCP
treatment (Golding et al., 1998), but lower SSCs in 1MCP treated fruit were associated with lower sucrose
concentrations (Defilippi et al., 2004).
3.3. Pigment metabolism
Loss of greenness, or yellowing, in most products is
inhibited by 1-MCP. For many products, especially
leafy vegetables and certain fruit such as apple, maintenance of green color is desirable in the marketplace as
yellowness is regarded as a sign of senescence.
However, for many fruit loss of chlorophyll and
development, or unmasking, of colored pigments is an
essential aspect of ripening (Kays, 1997). Therefore,
successful 1-MCP use requires a delay, but not
irreversible inhibition, of the processes involved in
pigment metabolism. 1-MCP inhibited anthocyanin
increases in strawberry fruit (Jiang et al., 2001), but
loss of chlorophylls and development of colors
(anthocyanins, lycopene) eventually reached desirable
levels of those of untreated fruit. However, yellowing of
banana fruit could be disrupted or incomplete and
uneven, even in the presence of propylene (Golding et
al., 1998; Harris et al., 2000; Macnish et al., 2000), and
there was a separation of color changes from other
ripening attributes in pears (Ekman et al., 2004).
Ethylene-induced degreening of 1-MCP-treated cucumbers was totally inhibited or occurred with development
of uneven yellowing (Nilsson, 2005).
Marty et al. (2005) used 1-MCP treatments to investigate ethylene regulation of carotenoid accumulation
and carotenogenic gene expression in orange and white
apricot cultivars. Both cultivars accumulated the colorless phytoene and phytofluene pigments, but β-carotene
accumulated only in the orange fruit. While1-MCP inhibited ethylene production of both cultivars, effects on
pigment accumulations were small.
Chlorophyll fluorescence changes were delayed in
1-MCP-treated fruit kept at ambient temperatures (Mir et
al., 2001; Jayanty et al., 2004). Little is known about the
effects of 1-MCP on pigment metabolism. However,
Gong and Mattheis (2003) and Hershkovitz et al. (2005)
have found that chlorophyllase activity was reduced in
1-MCP-treated broccoli florets and avocado fruit,
respectively.
3.4. Cell wall metabolism
For most products, delayed rather than complete
inhibition of softening, is desirable (Section 2). For non-
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
climacteric fruit such as strawberries and oranges, the
effects of 1-MCP on softening were usually not detectable (Porat et al., 1999; Tian et al., 2000), but softening was enhanced under some treatment combinations
with ethylene (Tian et al., 2000). Studies of 1-MCP on
cell wall changes of treated fruit are limited, but a number
of investigations on cell wall enzymes are available.
Decreased softening in 1-MCP-treated bananas is
associated with lower expression of an ethylene induced
expansin (MaExp1) gene (Trivedi and Nath, 2004), and
lower activities of pectin methylesterase (PME), polygalacturonase (PG), endo-β-1,4-glucanase (EGase) and
pectate lyase activities (Lohani et al., 2004). Effects of
1-MCP on softening of pears were associated with decreased β-galactosidase activity and differential effects
on expression of its genes (Mwaniki et al., 2005), lower
glycosidase activities (Trinchero et al., 2004), and
transcript accumulation of genes for PG1 and PG2,
but not EGase (Hiwasa et al., 2003). Delayed softening
of peaches was associated with delayed increases in
soluble pectin concentrations (Liu et al., 2005).
Activities of exo-PG and EGase were lower in 1-MCP
treated plums than in untreated fruit, but treatment did
not affect activities of endo-PG and pectin esterase (PE).
Alterations of cell wall enzyme associated with
enhanced susceptibility of peach fruit to a chilling
injury expressed as woolliness is discussed in Section
3.7.2.
Delayed softening of 1-MCP-treated avocado fruit
is reflected in similar patterns of delayed solubilization
and degradation of polyuronides (Jeong et al., 2002;
Jeong and Huber, 2004). Activities of PG and EGase
were lower in 1-MCP-treated fruit (Feng et al., 2000).
Interestingly PG activity did not recover even though
fruit softened to those comparable with control fruit
indicating that PG is not required for extensive
softening (Jeong et al., 2002). Changes of PME, αand β-galactosidase and EGase activities were delayed
but essentially followed patterns of increase or decline
of the untreated fruit (Jeong and Huber, 2004). Lower
activities of β-galactosidase, α-arabinofuranosidase
and β-xylosidase were associated with delayed
softening of 1-MCP treated kiwifruit (Boquete et al.,
2004).
1-MCP affected gene expression of cell wallrelated genes of the non-climacteric strawberry, but
specific effects depended on fruit ripening stage
(Balogh et al., 2005). 1-MCP treatment resulted in
up-regulation of a putative EGase in green fruit, but
its down-regulation in red fruit, up-regulation of a
ripening-repressed β-galactosidase, and down-regulation of pectic lyase gene.
401
3.5. Volatile compound metabolism
Flavor is a composite of taste and odor, and volatile
production can be greatly affected by ethylene. Therefore, decreased and/or altered volatile production in
1-MCP compared with untreated fruits may impact
product acceptability by consumers. However, sensory
analyses are limited to few products because of the
relatively recent registration of 1-MCP, and absence of
registration for many fruits and vegetables.
In apple fruit, ester production was inhibited by
1-MCP, but results for other components were variable,
perhaps reflecting different cultivars and storage conditions. Mattheis et al. (2005) found that production of
esters, alcohols, aldehydes, acetic acid and 1-methoxy4-(2-propenyl)benzene was inhibited by 1-MCP, but
their production increased when kept at room temperatures after long term storage. Esters and alcohols
were lower in 1-MCP-treated fruit than untreated fruit
(Defilippi et al., 2004; Kondo et al., 2005) but aldehydes
were not affected (Defilippi et al., 2004). Esters were
reduced but the proportions of alcohols and the aldehyde
2-hexenal in treated fruit were higher (Lurie et al., 2002).
CA storage also inhibits volatile production of apple
fruit. This inhibition was enhanced in 1-MCP-treated
fruit, but the dynamics of volatile change over time were
different in response to the two treatments (Mattheis et
al., 2005); the effects of CA increased, while those of
1-MCP decreased, over time. The concentrations of
branched but not straight-chained esters recovered in
1-MCP-treated fruit, though not to those of untreated
fruit (Mattheis et al., 2005) confirming earlier indications that sensitivity to ethylene action varies among the
pathways of ester production (Fan and Mattheis, 1999b).
Ethylene production clearly has some direct effects on
volatile production of fruit, and indeed continuous ethylene action is required for maximum volatile production
(Fan et al., 1998; Fan and Mattheis, 1999b). While the
mechanisms of 1-MCP action on volatiles are not
known, Defilippi et al. (2005) found that alcohol dehydrogenase (ADH) activity was not affected by 1-MCP,
but alcohol acyl transferase (AAT) transcripts and activity were lower in treated apple fruit suggesting that
modulation of this step in volatile synthesis by ethylene
may be responsible for lower ester production. Expression of four AAT genes were suppressed by 1-MCP
treatment of melons (El-Sharkawy et al., 2005).
In pear fruit, increases of ester and alcohol production
were delayed by 1-MCP, with quantitative differences
between long chain and branched esters, but volatiles were
similar in treated and untreated pear fruit when equally
ripe (Argenta et al., 2003). Total volatile production of
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C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
bananas was inhibited by 1-MCP treatment, and quantitatively, ester concentrations were decreased, while those
of alcohols were increased in treated fruit (Golding et al.,
1998). Abdi et al. (1998) found that aroma volatile
production of plums was ethylene-dependent or
-independent, depending on the cultivar. 1-MCP increased
acetaldehyde and ethanol accumulation in citrus resulting
in off-flavor development (Porat et al., 1999), but delayed
accumulation of these compounds in plums (Salvador et
al., 2003). Where reduced aroma is associated with
1-MCP treatment, the commercial implications are likely
to vary by product type, being more critical for products
and cultivars where aroma is a quality characteristic
expected by the consumer. For some products, certain
aromas are associated with over-ripening and therefore
their inhibition is desirable, or aroma concentrations may
be less important than texture and acid/sugar levels.
3.6. Nutritional quality
The effect of 1-MCP on nutritional quality has not
been studied thoroughly. However, 1-MCP slows
vitamin C loss in Chinese jujube (Jiang et al., 2004b),
peaches (Liu et al., 2005), pineapples (Selvarajah et al.,
2001), and minimally processed lettuce and pineapple
(Budu and Joyce, 2003; Tay and Perera, 2004). Although
phenolic contents of apples were not affected by 1-MCP
treatment (Defilippi et al., 2004), 1-MCP treated ‘Delicious’ and ‘Empire’ apples maintained higher watersoluble antioxidant activity than untreated fruit after cold
storage (MacLean et al., 2003). Lower phenolic and
anthocyanin contents in strawberry fruit treated with
high 1-MCP concentrations (Jiang et al., 2001) could
potentially reduce antioxidative activity.
3.7. Physiological storage disorders
3.7.1. Apple
The literature on physiological storage disorders is
greatest for apple fruit. 1-MCP can reduce senescent
breakdown (Watkins et al., 2000; DeLong et al., 2004;
Moran and McManus, 2005), brown core (syn. coreflush) (Fan and Mattheis, 1999a; Zanella, 2003), core
browning (DeLong et al., 2004), coreline browning
(Moran and McManus, 2005) and soft scald (Fan and
Mattheis, 1999a), which are variously disorders associated with senescence and cold storage. Dissipation of
watercore from fruit is reduced by 1-MCP treatment
(Watkins, unpublished data). Susceptibility of some
disorders appears to be increased by 1-MCP treatment,
although little research on these responses has yet been
published. An exception is external carbon dioxide
injury which is higher in 1-MCP-treated fruit than untreated fruit (DeEll et al., 2003; Zanella, 2003; Watkins
and Nock, 2004). The disorder is associated with early
harvested fruit and early exposure to carbon dioxide in
the storage atmosphere (Watkins et al., 1997; FernandezTrujillo et al., 2001) and the effect of 1-MCP is consistent
with maintenance of the fruit in a less ripe state and thus
more susceptible to injury. Risk of injury is eliminated by
use of the antioxidant diphenylamine (DPA), registered
to control superficial scald, or reduced by maintaining
very low carbon dioxide concentrations in the storage
atmosphere for the first few weeks of storage (Watkins
and Nock, 2004).
Some interactions of 1-MCP with other technologies
have been investigated: Fan and Mattheis (2001) found
that irradiation damage was aggravated in 1-MCP-treated fruit when they were kept at 20 °C. Lu and Toivonen
(2003) showed a synergistic benefit of 1-MCP and 35%
CO2 on quality of ‘Gala’ apples, without injury.
Most research focus of 1-MCP and disorders of apple
has been on superficial scald (syn. storage scald) because
of the interaction between ethylene production and that
of α-farnesene, and early reports that 1-MCP inhibited
disorder development (Fan and Mattheis, 1999a,b;
Rupasinghe et al., 2000; Watkins et al., 2000). Superficial scald is a physiological storage disorder of susceptible apple and pear cultivars that is manifested as
browning or blackening of the skin resulting from necrosis of the hypodermal cells (Bain and Mercer, 1963).
Development of the disorder occurs during low
temperature storage and it is thought to be a chilling
injury (Watkins et al., 1995). Injury to cells probably
results from free radical reactions associated with the
oxidation of α-farnesene to conjugated trienols (CTols),
predominantly 9E and 9Z isomers of 2,6,10-trimethyldodeca-2,7,9,11-tetraen-6-ol (Rowan et al., 1995; Whitaker et al., 1997). Accumulation of α-farnesene in the
skin is associated with ethylene (Du and Bramlage,
1994; Watkins et al., 1995; Whitaker et al., 2000).
Development of scald can be reduced or prevented by
inhibiting α-farnesene production or its accumulation,
e.g., by ventilation, use of oil wraps, or by inhibiting its
oxidation to CTols by DPA (Huelin, 1968; Lurie et al.,
1989). It has been well demonstrated that inhibition of
scald by 1-MCP is associated with inhibition of αfarnesene accumulation that restricts substrate available
for oxidation (Fan and Mattheis, 1999a; Rupasinghe et
al., 2000; Watkins et al., 2000; Shaham et al., 2003;
Arquiza et al., 2005; Pechous et al., 2005).
Although it may not be considered a storage disorder
sensu stricto, an undesirable feature of some apple cultivars is development of greasiness, or slipperiness to
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
touch, which is disliked by consumers. Greasiness is
associated with changes in the wax and oil fractions in
the skin (Morice and Shorland, 1973), and in susceptible
cultivars, its development can occur in more mature fruit
and with longer storage periods (Leake et al., 1989a,b).
1-MCP inhibited development of greasiness (Fan and
Mattheis, 1999a; Watkins and Nock, 2005) suggesting
that it may be a useful tool to manage the problem.
3.7.2. Other fruits and vegetables
Development of superficial scald in pear fruit was
also controlled by 1-MCP, but developed as fruit were
released from inhibition of ripening (Ekman et al., 2004).
Thus, total control of the disorder only occurred in fruit
that did not ripen. 1-MCP inhibited production of αfarnesene and its oxidation product, MHO, in pears
(Argenta et al., 2003). Other disorders of pears that are
inhibited by 1-MCP include senescent scald and core
browning (Argenta et al., 2003), watery and core
browning (Calvo and Sozzi, 2004), senescent breakdown (Kubo et al., 2003), internal breakdown (Ekman et
al., 2004) and decay (Argenta et al., 2003).
Incidences of low temperature disorders of a number
of fruit were reduced by 1-MCP treatment, including
internal flesh browning in avocado (Pesis et al., 2002;
Hershkovitz et al., 2005; Woolf et al., 2005), and pineapple (Selvarajah et al., 2001), and chilling injury of
citrus fruit (Dou et al., 2005). Reduced browning in
avocados was associated with reduced polyphenol oxidase (PPO) and peroxidase (POD) activities (Pesis et al.,
2002; Hershkovitz et al., 2005).
In contrast, the chilling injuries, internal browning,
flesh woolliness and reddening were increased by
1-MCP treatment in peaches and nectarines (Dong et
al., 2001b; Fan et al., 2002; Girardi et al., 2005). Development of woolliness was associated with lower accumulations of transcripts for ACO, and associated
decreases of those encoding PG, PE, while that of
EGase was increased. 1-MCP enhanced these effects
suggesting that a certain level of ethylene production by
fruit is required for normal ripening after storage (Dong
et al., 2001b). A slight increase in internal reddening
occurred in 1-MCP-treated plums (Dong et al., 2002),
but no effects of 1-MCP on internal browning and flesh
gelling, have been reported. 1-MCP-treated ‘Shamouti’
oranges (Porat et al., 1999) and banana fruit (Jiang et al.,
2004a) are also more sensitive to chilling injury. In
untreated banana fruit stored at chilling-inducing temperatures, the development of injury was associated with
decreased ethylene binding. 1-MCP treatment further
decreased ethylene binding, and Jiang et al. (2004a)
suggested that enhanced chilling injury of bananas was
403
associated with decreased responses of the fruit to
ethylene.
1-MCP treatment prevents ethylene induced development browning and chemical changes in lettuce and
carrots. 1-MCP delayed ethylene-induced russet spotting of whole and minimally processed lettuce, and
browning of the cut surfaces of shredded lettuce (Wills
et al., 2002; Saltveit, 2004; Tay and Perera, 2004).
Interestingly, while these disorders are associated with
induction of phenypropanoid metabolism and greater
accumulation of phenolic compounds, 1-MCP did not
interfere with wound-induced browning (Saltveit,
2004). 1-MCP-treated carrots had inhibited accumulation of 8-hydroxy-3-methoxy-3,4-dihydro-isocoumarin,
associated with bitter flavors and the phytoalexin, 6methoymellin (Fan and Mattheis, 2000; Fan et al.,
2000). 1-MCP prevented ethylene-induced water-soaking of watermelon and the associated increase in
phospholipid (phosphatidylcholine and phosphatidylinositol) degradation and activities of phospholipases C,
phospholipases D and lipoxygenase (Mao et al., 2004).
Postharvest pitting of citrus fruit was inhibited by 1MCP (Dou et al., 2005).
3.7.3. A physiological basis for disorder development in
response to 1-MCP
The effects of 1-MCP on disorders of fruit and vegetables can be categorized into several types:
a. Disorders that are associated with senescence and
therefore are prevented by inhibition of ethylene
production. These include disorders such as senescent breakdown of apple fruit, which are reduced by
1-MCP-induced slowing of senescence processes.
b. Chilling-related disorders that are inhibited when
ethylene production is prevented. Examples include
superficial scald of apples, and internal flesh
browning of avocado and pineapple.
c. Chilling-related disorders that are increased by
inhibition of ethylene production. Examples include
woolliness (mealiness) and internal breakdown in
peach and nectarines, and chilling injury in citrus,
suggesting that these disorders are aggravated if
normal ripening processes mediated by ethylene are
prevented.
d. Ethylene-induced disorders that are inhibited by
1-MCP application. These include browning
responses in lettuce, increases in undesirable chemical changes such as isocoumarin accumulation in
carrots, and water-soaking of watermelon.
e. Disorders associated with CA storage, e.g., CO2
injury of apple fruit, which is enhanced by 1-MCP.
404
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
3.8. Pathological storage disorders
1-MCP increased disease susceptibility of avocado
(Hofman et al., 2001; Adkins et al., 2005; Woolf et al.,
2005), custard apple, mango and papaya (Hofman et al.,
2001). Treatment of strawberry fruit with higher 1-MCP
concentrations also increased decay (Ku et al., 1999). In
citrus fruit, 1-MCP inhibited decay at low concentrations, but enhanced it at high concentrations (Dou et al.,
2005). Also, in citrus, 1-MCP increased mold rots caused
by Penicillium digitatum and P. italicum (Porat et al.,
1999; Marcos et al., 2005) and stem rots caused by
Diplodia natalensis (Porat et al., 1999). In contrast,
Mullins et al. (2000) found no effect of 1-MCP on
progression of P. digitatum growth on innoculated
grapefruit.
Susceptibility of apples to bitter rot (Colletotrichum
acutatum) and blue mold (P. expansum) was higher in
1-MCP treated than untreated fruit (Janisiewicz et al.,
2003). 1-MCP slightly increased severity of decay in
fruit inoculated with P. expansum, especially when used
in conjunction with other stress treatments such as prestorage heat (Leverentz et al., 2003). Saftner et al. (2003)
found that 1-MCP with or without pre-storage heat
treatment reduced decay due to wound-inoculation by P.
expansum, Botrytis cinerea, C. acutatum at the time of
harvest and after CA storage, probably by maintaining
firmness and thereby resistance to infection.
Decay incidence of peaches after inoculation with P.
expansum was slightly reduced by 1-MCP treatment, and
it was suggested that resistance in these fruit was related
to higher activities of PAL, PPO and POD (Liu et al.,
2005). Reduced decay caused by brown rot, Monilinia
laxa, was found in 1-MCP-treated plums (Menniti et al.,
2004). In strawberry, decay was more rapid in 1-MCP
treated fruit (Bower et al., 2003), while Ku et al. (1999)
found inhibited decay at low 1-MCP concentrations and
enhanced decay with treatments of 500–1000nl l− 1.
Increased disease susceptibility in fruit treated with high
1-MCP concentrations may be associated with lower
phenylalanine ammonia lyase (PAL) activity and lower
phenolic contents (Jiang et al., 2001).
Relatively little about 1-MCP effects on disease
incidence is known, but it is likely to become an important factor in the less ideal environments that exist in
the commercial world compared with laboratory-based
experimental systems. Factors that influence the effects
of 1-MCP on disease development are likely to be
specific to the product and its interaction with the specific pathogen and the environment. Delayed ripening
associated with reduced ethylene production may increase product resistance to infection and lesion devel-
opment. However, sensitivity can be beneficial against
some pathogens but deleterious to resistance against
other pathogens. Small amounts of endogenous ethylene
may be necessary to maintain basic levels of resistance to
environmental and pathological stress because of its
involvement in regulation of plant defense genes
(Marcos et al., 2005).
4. Summary
The discovery and subsequent commercialization of
1-MCP has provided exciting opportunities for postharvest scientists to gain insight into the fundamental
processes that are involved in ripening and senescence
of fruit and vegetables. Prospects for commercialization
of 1-MCP for several products appear high. For products
such as most vegetables and perhaps non-climacteric fruit,
where further senescence (e.g., yellowing) will decrease
product value, 1-MCP applications that prevent any
change are desirable. However, for products such as many
climacteric fruit, success will be based on delaying rather
than preventing ripening, in order to provide a product
that meets consumer requirements. Data obtained thus far
for the apple show that the issues associated with
commercialization are not trivial and provide an exciting
era for postharvest researchers as they aid horticultural
industries to realize the full potential for 1-MCP. Under
commercial conditions, handling practices will need to
take into account many factors including commodity type,
cultivar, maturity or ripeness stage, time between harvest
and treatment, treatment temperature, and desired effects
on quality. Each of these factors can affect the 1-MCP
concentrations that should be applied to each product.
Whether 1-MCP concentrations that will allow beneficial
delays in ripening, while still allowing positive aspects of
ethylene action to occur, can be optimized to meet
conditions associated with pre- and post-harvest variations of some products is still uncertain.
Commercial utilization of this technology will also be
a function of the cost of 1-MCP application relative to its
benefits for each product. The cost / benefit ratio will be
affected by many factors including the product response,
especially in relation to quality as perceived by the
consumer, how successfully 1-MCP use can be incorporated into handling, storage and transport systems, the
scale of the industry involved, competition in the
marketplace, and whether it provides access to markets
that are not available using current technologies.
In summary, the availability of 1-MCP is likely to
have a dramatic impact on our understanding of the
involvement of ethylene in plant metabolism as well as
the storage and handling of horticultural products.
C.B. Watkins / Biotechnology Advances 24 (2006) 389–409
Senescence and ripening processes are complex, however, and even more under commercial conditions where
many other factors come into play. As shown for the
apple, the strengths and limitations of this compound “in
the real world” will only be fully appreciated when it
becomes commercially available for other horticultural
products around the world.
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