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 : selvashanthi@yahoo.com (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. / 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. / 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. / 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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Slack, P.T. (Ed.), 1987. Analytical Methods Manual, 2nd ed. British Food Manufacturing Industries Research Associa- tion, Leatherhead, UK. Teisson, C., 1979. Internal browning of pineapples: I. History; II. Materials and Methods. Fruits 34, 245–261. Vendrell, M., McGlasson, W.B., 1971. Inhibition of ethylene production in banana fruit tissue by ethylene treatment. Aust. J. Biol. Sci. 24, 885–895. Watkins, C.B., Nock, J.F., Whitaker, B.D., 2000. Responses of early, mid and late season apple cultivars to postharvest application of 1-methylcyclopropene (1-MCP) under air and controlled atmosphere storage conditions. Postharvest Biol. Technol. 19, 17–32. . 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. 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. (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