Internal browning in cold stored pineapples is suppressed by

Postharvest Biology and Technology 23 (2001) 167–170
www.elsevier.com/locate/postharvbio
Short communication
Internal browning in cold-stored pineapples is suppressed by
a postharvest application of 1-methylcyclopropene
S. Selvarajah *, A.D. Bauchot, P. John
Department of Agricultural Botany, School of Plant Sciences, The Uni6ersity of Reading, Reading RG
66
AS, UK
Received 25 October 2000; accepted 13 February 2001
Abstract
Treatment with 1-methylcyclopropene (1-MCP), the inhibitor of the ethylene receptor, at 0.1 ppm (4.5 nmol l
−1
)
for 18 h at 20°C effectively controlled internal browning, a chilling injury symptom, in pineapples stored at 10°C for
four weeks. The treatment with 1-MCP also delayed ascorbic acid decline, and arrested the decline in both total
soluble solids and ethylene synthesis. The present findings throw light on the role of ethylene in internal browning,
and suggest that 1-MCP could be considered for use commercially to control this important postharvest physiological
disorder in pineapples. © 2001 Elsevier Science B.V. All rights reserved.
Keywords
:
1-Methylcyclopropene; Ananas comosus L.; Ethylene; Internal browning; Chilling injury
1. Introduction
Internal browning (IB, also known as endoge-
nous brown spot or black heart) is the most
important physiological disorder of pineapples
that are stored below 13°C (Dull, 1971), limiting
both the storage and the export of this fruit.
Partial control only has been achieved after har-
vest by various treatments (Paull and Rohrbach,
1985; Selvarajah and Herath, 1997; Selvarajah et

al., 1997, 1998).
1-Methylcyclopropene (1-MCP) is an inhibitor
of ethylene perception that binds irreversibly to
the ethylene-binding protein (Sisler and Serek,
1997). Since it is non-toxic (Technical Bulletin,
Rohm and Haas Company) and odourless, 1-
MCP is potentially of commercial value to control
ethylene-dependent postharvest disorders. Direct
involvement of ethylene in pineapple IB has not
been reported, but chilling injury is known to be
associated with ethylene synthesis (Ben-Amor et
al., 1999), even in non-climacteric fruit (McCol-
lum and McDonald, 1991). Thus there appeared
to be a basis for testing the effectiveness of 1-
MCP in controlling IB in pineapple. Here we
report that 1-MCP strongly reduces the incidence
of IB in pineapple.
* Corresponding author. Tel.: +44-118-9318098; fax: +44-
118-9316577.
E-mail address
:
(S. Selvarajah).
0925-5214/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0925-5214(01)00099-0
S. Sel6arajah et al.
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Posthar6est Biology and Technology
23 (2001) 167 – 170
168
2. Materials and methods

‘Queen’ pineapples (Ananas comosus. L) from
South Africa were transported within three days
to our laboratory. Fruit of uniform shape, size,
colour and weight were selected and placed indi-
vidually in 6.7 l sealed plastic containers. One set
of fruits was exposed to 0.1 ppm (4.5 nmol l
−1
)
1-MCP generated by EthylBloc
®
at 20°C for 18 h
(80– 90% RH). Control fruit were subjected to the
same conditions without exposure to 1-MCP. Fol-
lowing treatment, all the pineapples (treated and
control) were stored at 10°C (70– 80% RH).
Fruits were analysed for IB intensity, ripeness
stage and other quality parameters immediately
upon arrival and then after 1 –4 weeks of storage
at 10°C followed by 3 days shelf-life at 20°C
(60– 70% RH). For each assessment, 10 fruit
treated with 1-MCP were compared with 10 con-
trol fruit. The trial was repeated twice, in early
May and at the end of June, and the results were
pooled.
The fruit were cut longitudinally in half and the
incidence of IB was determined. For each fruit, IB
intensity was scored from 0 to 5 according to the
percentage of flesh affected (0, free from IB; 0.5,
watery spots; 1-5: B 10, 10– 25, 25– 50, 50–75
and \ 75% of the flesh discoloured, respectively;

Teisson, 1979). The average IB intensity was cal-
culated for each lot of fruit.
The stage of ripeness was determined by visual
assessment of the shell (Rangana 1977). The scale
ranges from 0 to 5: 0, all eyes are totally green; 1,
B 20% of the eyes are predominantly yellow; 2,
20– 40% of the eyes are tinged with yellow; 3, up
to 65% of the eyes are predominantly yellow; 4,
65– 90% of the eyes are fully yellow; 5, \ 90% of
the eyes are fully yellow and no more than 20% of
the eyes are reddish orange. Fruit with \ 20% of
the eyes reddish orange were considered as senes-
cent and discarded.
Each fruit was weighed upon arrival and after
storage at 10°C followed by 3 days shelf-life at
20°C. The total soluble solids (TSS, expressed as
% Brix) of fruit juice was determined using a
hand-held refractometer (0–30% Brix). Ascorbic
acid was determined by HPLC (Slack, 1987). Eth-
ylene emission was monitored by incubating indi-
vidual fruits in plastic containers at 10°C and was
measured by gas chromatography after a 2 h
incubation.
3. Results
After only 1 week of storage at 10°C followed
by 3 days shelf-life, 50% of the control pineapples
showed IB, and after 3 weeks storage all were
severely affected (Fig. 1A). Treatment with 1-
Fig. 1. Effect of 1-MCP on internal browning incidence (A)
and intensity (B), and ripeness (C) of pineapples stored at

10°C followed by 3 days at 20°C. Asterisks indicate a signifi-
cant difference between the 1-MCP treatment and the control
at PB 0.01.
S. Sel6arajah et al.
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Posthar6est Biology and Technology
23 (2001) 167 – 170
169
Fig. 2. Effect of 1-MCP on ethylene production of pineapples
during storage at 10°C. Vertical lines represent standard error
of the means and are not shown when the values are smaller
than the symbol.
(Sisler and Serek, 1997). Thus, we assume that the
effects of 1-MCP reported here are due to 1-MCP
blocking the ethylene receptors of pineapple. Al-
though IB in pineapple has not previously been
directly demonstrated to be due to ethylene, the
present results clearly show that ethylene percep-
tion is a necessary step for pineapple to develop
chilling injury symptoms. 1-MCP has already
been shown to dramatically reduce postharvest
chilling injury in climacteric fruits such as melon
(Ben-Amor et al., 1999) and apple (Rupasinghe et
al., 2000; Watkins et al., 2000), but was not
effective on non-climacteric orange (Porat et al.,
1999).
Besides inhibiting IB development, exposure to
1-MCP stimulated ethylene production in cold-
stored pineapples. Sisler and Blankenship (1993)
already reported a greater capacity for ethylene

production when the ethylene receptors were inac-
tivated in mung bean seedlings. Moreover, stimu-
lation of the receptor by ethylene treatments led
MCP completely eliminated IB for the first 3
weeks of cold storage, and reduced the incidence
to 20% at week 4 (Fig. 1A) with an even more
marked effect on the intensity of browning (Fig.
1B).
Treatment with 1-MCP also delayed shell ripen-
ing, as measured by the eye colour (Fig. 1C). In
the control fruit, 65% of the eyes turned yellow
(scored as index 3) within 2 weeks, while it took 4
weeks for the 1-MCP treated fruit to reach this
stage. The 1-MCP treated fruit did not begin to
ripen until more than 2 weeks in storage.
Control cold-stored pineapples showed a rapid
decline in the rate of ethylene synthesis. The
decline in rate of ethylene synthesis was also
significantly slowed by the 1-MCP treatment (Fig.
2).
The rapid rate of ascorbic acid decline in
pineapples was significantly delayed by the 1-
MCP treatment (Fig. 3A). The ascorbic acid levels
in the control fruit after one week were reached
only after four weeks of storage in 1-MCP treated
fruit (Fig. 3A). Treatment with 1-MCP also ar-
rested the decline in TSS (Fig. 3B) and limited the
weight loss compared to the control fruit (PB
0.01, t-test; data not shown).
4. Discussion

It is widely accepted that 1-MCP binds to the
ethylene receptors, and blocks ethylene perception
Fig. 3. Effect of 1-MCP on the content of ascorbic acid (A)
and total soluble solids (B) of pineapples stored at 10°C
followed by 3 days at 20°C. Vertical lines represent standard
error of the means and are not shown when the values are
smaller than the symbol.
S. Sel6arajah et al.
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Posthar6est Biology and Technology
23 (2001) 167 – 170
170
to a decrease in ethylene production in immature
banana (Vendrell and McGlasson, 1971). The
phenomenon is known as auto-inhibition of ethyl-
ene production. It is compatible with our observa-
tion that 1-MCP treatment induced ethylene
production in pineapple.
In addition, 1-MCP delayed shell yellowing by
two weeks, as previously observed for cold-stored
orange peel (Porat et al., 1999). This confirms the
involvement of ethylene perception in non-climac-
teric fruit degreening. It also suggests that 1-MCP
inhibited ethylene perception for between two and
three weeks in pineapple.
In conclusion, the suppression of IB demon-
strated here suggests that 1-MCP could be consid-
ered for commercial application in controlling this
widespread disorder during the storage and trans-
port of pineapples.

Acknowledgements
We thank Safeway for providing fruits and
Rohm and Haas Company for kindly providing
EthylBloc. We are grateful to Sue Mitchell and
Jennifer Greenham for expert technical advice.
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