Internal browning in cold stored pineapples is suppressed by

John Department of Agricultural Botany, School of Plant Sciences, The Uni 6ersity of Reading, Reading RG6 6 AS, UK Received 25 October 2000; accepted 13 February 2001 Abstract Treatment

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 Uni 6ersity of Reading, Reading RG6 6 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.: + 118-9318098; fax: +

44-118-9316577.

E-mail address: selvashanthi@yahoo.com (S Selvarajah).

0925-5214/01/$ - see front matter © 2001 Elsevier Science B.V All rights reserved.

PII: S 0 9 2 5 - 5 2 1 4 ( 0 1 ) 0 0 0 9 9 - 0

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: B10, 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,

B20% 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 PB0.01.

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.

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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