The application of ethanol vapours has been optimised over two seasons in order to prevent rot development, caused by Botrytis cinerea, and stem browning in 'Chasselas' table grapes. At a dose rate of 2 ml per kg of grapes, ethanol vapour was as effective as sulphur dioxide pads. Consumer panels detected no significant difference in sensory perception between controls and treated grapes. The ethanol vapour treatment could be easily implemented by the table grape industry since the technology is similar to sulphur dioxide treatment

Chervin, Christian

Monteils, Ghislaine

Westercamp, Pascale

English

International audienceThe application of ethanol vapours has been optimised over two seasons in order to prevent rot development, caused by Botrytis cinerea, and stem browning in 'Chasselas' table grapes. At a dose rate of 2 ml per kg of grapes, ethanol vapour was as effective as sulphur dioxide pads. Consumer panels detected no significant difference in sensory perception between controls and treated grapes. The ethanol vapour treatment could be easily implemented by the table grape industry since the technology is similar to sulphur dioxide treatment

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Ethanol vapours limit Botrytis development over the postharvest life of table grapes

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 1 Ethanol vapours limit Botrytis development over the postharvest life of 1 table grapes 2  3  4 Christian Chervin1, Pascale Westercamp2 and Ghislaine Monteils2 5 1UMR 990, INRA/INP-ENSAT, BP 107, 31326 Castanet, France 6 2CTIFL-CEFEL, 49 Chemin des Rives, 82000 Montauban, France 7 Corresponding author: chervin@ensat.fr 8  9 Abstract:  10 The application of ethanol vapours has been optimised over two seasons in order to prevent 11 rot development, caused by Botrytis cinerea, and stem browning in 'Chasselas' table grapes. 12 At a dose rate of 2 ml per kg of grapes, ethanol vapour was as effective as sulphur dioxide 13 pads. Consumer panels detected no significant difference in sensory perception between 14 controls and treated grapes. The ethanol vapour treatment could be easily implemented by the 15 table grape industry since the technology is similar to sulphur dioxide treatment.  16  17  18 Introduction 19  20 Table grapes are routinely treated with sulphur dioxide (SO2) to reduce the incidence of 21 postharvest decay, largely caused by Botrytis cinerea (Lichter et al.,2002), during storage and 22 transportation. By limiting rot development, the SO2 treatments allow to keep the grapes at 23 high humidity thus limiting stem browning, that is mainly due to desiccation. However SO2 24 treatment may cause damage to the grape berries (discolouration, off-flavours), and sulphite 25 residues are not acceptable to some consumers.  26  2 Ethanol is known to influence ripening and senescence in some fruit plant tissues (Podd and 27 Staden, 1998), to reduce postharvest fungal decay (Gabler and Smilanick, 2001) and to kill 28 insect pests (Dentener et al., 1998).  Application of ethanol to table grapes by dipping has 29 been shown to effectively improve storage life, mainly by limiting postharvest rot 30 development (Lichter et al., 2002; Karabulut et al., 2003).  We have already investigated the 31 efficacy of ethanol vapours to control rots.  Preliminary results indicated that the optimal 32 ethanol dose for effective disease control was less than 5 ml.kg-1 of fruit (Chervin et al., 33 2003). Since stem browning was higher at 5 ml ethanol.kg-1 compared to SO2 treatments, we 34 conducted new experiments in order to find a lower dose of ethanol that would still control rot 35 development without too high stem browning as in commercial SO2 treatments,. In addition to 36 the optimisation of the ethanol dose, we also report on the use of a simple system to generate 37 ethanol vapours with pre-soaked paper pads. 38  39 Material and methods 40 'Chasselas' table grapes (Vitis vinifera, L.) were picked in a local vineyard (Montauban, 41 France) the second fortnight of September in 2002 and 2003 (at 20% Brix and 3.5 g.l-1 tartaric 42 acid), and packed in wooden boxes (dimensions 40 x 28 x 12 cm) each containing 4 kg of 43 fruit. In the first year of experimentation (2002) there were five treatments: an untreated 44 control, one SO2 pad per box (7 g Na2S2O5), ethanol 1.25 ml.kg-1, ethanol 3.75 ml.kg-1 and 45 ethanol 7.5 ml.kg-1. Each box was a replicate and there were three replicates per treatment. All 46 boxes were wrapped with individual polyethylene bags, then stored at 0°C for four weeks. In 47 2003 there were four treatments: an untreated control, one SO2 pad per box, ethanol 2 ml.kg-1 48 and ethanol 4 ml.kg-1. All boxes were wrapped with individual polyethylene bags. The boxes 49 were sealed and stored as described above then assessed after four and seven weeks.   50 The ethanol vapours were generated by pre-soaking newspaper sheets (40 x 28 cm) in various 51 quantities of ethanol in order to reach the rate in ml.kg-1. The sheets were left in contact with 52  3 ethanol in a sealed plastic bag for two hours to allow equilibrium of the ethanol into the paper 53 sheet. During fruit packing operations, a macro-perforated plastic sheet was placed between 54 the paper sheet and the grapes to prevent direct contact. Ethanol concentration in the box 55 headspace was measured with a Dräger pump (Dräger Sicherheitstechnik, Lübeck,   56 Germany) fitted with specific glass tubes (Chip Dräger Ethanol 100 - 2500 ppm  ref. 57 6406370).   58 At the end of each storage period, the bags were removed and boxes were left at 8°C for half 59 an hour to limit condensation on the fruit, then transferred to ambient temperature (20°C) for 60 three days.  Botrytis incidence was visually assessed by counting the number of affected 61 berries per bunch on all the bunches in each box. In the first experiment, when the average 62 number of rotten berries per bunch exceeded 5, the bunch was considered as "rejected", i.e. 63 not suitable for sale. During the second year experiment, the rotten berries of each box were 64 weighed and the result expressed as a percentage of the grape total weight in the box. 65 The assessment of stem browning was performed visually using the following 0 to 5 scale: the 66 scores were 0, 1, 2, 3, 4, and 5 for stem browning being <10%, 10 to 30 %, 30 to 50 %, 50 to 67 70%, 70 to 90% and > 90%, respectively. 68 Sensory analyses were performed with consumer-type panellists, using a hedonic scale 69 derived from Poste et al. (1991). The scale for sensory appreciation was a continuous line of 70 10 cm and the extremities at each end of the scale were: "I dislike extremely" (equivalent to 0) 71 and "I like extremely" (equivalent to 10). The 20 to 25 panellists in each session were asked 72 to mark the scale line with a pencil tick to give an indication of their appreciation. The 73 advantage of the continuous scoring system is that it suits most of the parametric statistical 74 tests. The samples were presented to them in a given order and were coded with five digit 75 numbers. There were as many different tasting orders as possible, as we appreciate  food as a 76 function of what we ate before. The tasting sessions were performed after lunch. 77  4 The differences between treatments were analysed by ANOVA and LSD using SigmaStat 78 3.0.1 (SPSS, Chicago, IL, USA). 79  80 Results and Discussion 81  82 Ethanol vapour at doses equal or higher than 3.75 ml.kg-1 resulted in grapes to a similar 83 commercial standard as SO2 treatment after the four week storage (Table 1). However rots 84 caused by B. cinerea were not effectively controlled after seven weeks of cold storage (data 85 not shown). There was no significant difference (P> 0.05) in stem browning between the 86 control, 1.25 ml.kg-1, 3.75 ml.kg-1 and SO2 treatments after four weeks of storage, and ethanol 87 at 7.5 ml.kg-1 tended to increase stem browning (data not shown), suggesting that high dose 88 rates may induce phytotoxicity. The dose rate of 3.75 ml ethanol per kg of fruit gave 89 headspace concentrations of 220 ± 80 ppm of ethanol, over four weeks of storage at 0°C, and 90 this dose was sufficient to ensure fruit quality and control rot development without increasing 91 stem browning. Co-workers at the experimental station in Montauban detected a slight 92 ethanol taint with grapes treated with ethanol at 3.75 and 7.5 ml.kg-1, so further  sensory 93 analyses were carried out on grapes treated with ethanol doses between 1.25 and 3.75 ml.kg-1. 94  95 The following year, both ethanol doses (2 and 4 ml.kg-1) and the SO2 pad treatments 96 significantly (P<0.05) reduced the rot development in comparison to the control  and there 97 was no significant (P>0.05) difference between SO2 and the ethanol treatments (Figure 1a). 98 All three treatments significantly (P<0.05) reduced stem browning (Figure 1b) compared to 99 the control, but SO2 and ethanol at the low dose of 2 ml.kg-1 were significantly (P<0.05) more 100 effective at reducing this disorder compared to ethanol at the high dose of 4 ml.kg-1.  101 The sensory analyses showed that no consumer would detect a difference between postharvest 102 treated berries by visually assessing the samples (Figure 1c). However SO2 treated grapes 103  5 were significantly (P<0.05) less appreciated than the controls when assessors tasted the grape 104 samples (Figure 1d). The results obtained after four weeks cold storage and three days at 20°C 105 followed a similar pattern  (data not shown). 106  107 In the preliminary study (Chervin et al., 2003), we showed that ethanol vapours also had the 108 potential to reduce berry shatter. It would be worth checking this with other cultivars than 109 ‘Chasselas’. 110  111 Overall our results confirm that ethanol has a potential for improving postharvest shelf-life of 112 table grapes, whether it is applied during a dipping treatment (Lichter et al., 2002) or with a 113 pad generating vapours (e.g. a paper impregnated with liquid ethanol). Ethanol could be used 114 in conjunction to SO2, and this may allow a reduction of the dose of this latter, however 115 further research is necessary to develop this combination. Further developments may include 116 silica gel imbibed with alcohol, as previously described by Suzuki et al. (2004). 117  118 Acknowledgements:  We wish to thank the Midi-Pyrénées regional council for a research 119 grant, Daniel Lavigne and Marie-Eve Biargues (CEFEL) for providing the grapes and helping 120 with quality assessment, Dr Patrick Varoquaux (INRA) for providing advices and plastic 121 films for the experimental set-up, Pr Jean-Claude Pech and Dr Alain Latché (ENSAT) for 122 their support, and the students Gaëlle Pierdet, Clément Pagès, Benoit Knibiehler, Mikaël 123 Coquiller and Magalie Tanguy (ENSAT) for helping along the two season experiment, and Dr 124 John Golding (NSW Agriculture) for comments and edition of the manuscript. Finally, thanks 125 to anonymous referees for their time and comments. 126  127  128  129  6 Literature cited 130 Chervin, C., Westercamp, P., El-Kereamy, A.,  Rache, P., Tournaire, A.,  Roger, B., Goubran, 131 F., Salib, S. and  Holmes, R., 2003. Ethanol vapours to complement or suppress sulfite 132 fumigation of table grapes. Acta Hort., 628, 779-784.  133 Dentener, P. R.  Alexander, S. M.  Bennett, K. V.  and McDonald, R. M., 1998.  Postharvest 134 control of lightbrown apple moth using ethanol. Acta Hort., 464, 279-284. 135 Gabler, F. M. and  Smilanick, J. L. 2001. Postharvest control of table grape gray mold on 136 detached berries with carbonate and bicarbonate salts and disinfectants. Amer. J. Enol. 137 Vitic., 52, 12-20. 138 Karabulut, O.A., Smilanick, J.L., Gabler, F.M., Mansour, M. and Droby, S., 2003.  Near-139 harvest applications of Metschnikowia fructicola, ethanol, and sodium bicarbonate to 140 control postharvest diseases of grape in central California. Plant Dis., 87, 1384-1389. 141 Lichter, A., Zutkhy, Y., Sonego L., Dvir O., Kaplunov T., Sarig P. and Ben-Arie R., 2002. 142 Ethanol controls postharvest decay of table grapes. Postharvest Biol. Technol., 24, 143 301-308. 144 Podd, L. A.  and Staden, J. van., 1998. The role of ethanol and acetaldehyde in lower 145 senescence and fruit ripening - a review. Plant Growth Regul., 26, 183-189. 146 Poste, L.M., Mackie, D.A., Butler, G. and Larmond E., 1991. Hedonic scaling test. 147 Laboratory Methods for Sensory Analysis of Food, ed. Agriculture Canada, 148 publication 1864/E, pp. 64-67. 149 Suzuki, Y., Toshikazu, U. and Terai H. 2004. Inhibition of senescence in broccoli florets with 150 ethanol vapor from alcohol powder. Postharvest Biol. Technol., 31, 177-182. 151  7 Table and Figure captions 152 Table 1: Percentage of weight of table grapes (cv. Chasselas), accepted for sale as a function 153 of Botrytis development. Grape bunches were visually assessed in 2002 after four 154 weeks of storage at 0°C plus three days at 20°C. The ethanol (EtOH) doses applied 155 over cold storage are in ml per kg of fruit and the SO2 was applied using a 156 commercially available pad, LSD = least significant difference. 157 Treatment Control EtOH 1.25 EtOH 3.75 EtOH 7.5 SO2 LSD % accepted 10.7 35.2 89.5 84.8 85.0 23.9  158  159  160 Figure 1: Percentage of Botrytis infected berries (a) and severity of stem browning (b) as a 161 function of SO2 or ethanol treatments (EtOH) after seven weeks at 0°C and three days 162 at 20°C in 2003. Sensory evaluation of treated grapes by visual assessment (c) and 163 tasting (d), using 0 to 10 scales.  The ethanol doses are quantities in ml per kg of fruit 164 and SO2 was applied using a commercially available pad. Error bars represent standard 165 error of the mean. LSD = least significant difference. 166  167  168  8 d 169 Figure 1 Control SO2EtOH 2 mlEtOH 4 mlStem browning012345LSD0.05Botrytis infected berries (%)0510152025LSD0.05b) a) Control SO2EtOH 2 mlEtOH 4 mlTasting acceptance2345678Visual acceptance2345678LSD0.05LSD0.05c) Treatments d) 

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Ethanol vapours limit Botrytis development over the postharvest life of table grapes

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