ARTICLE IN PRESS. Development of new palladium-promoted ethylene scavenger

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1 Postharvest Biology and Technology xxx (2007) xxx xxx Development of new palladium-promoted ethylene scavenger Leon A. Terry a,, Thomas Ilkenhans b, Stephen Poulston b, Liz Rowsell b, Andrew W.J. Smith b a Plant Science Laboratory, Cranfield University, Bedfordshire MK45 4DT, UK b Johnson Matthey Technology Centre, Blount s Court, Sonning Common, Reading, Berkshire RG4 9NH, UK Received 18 October 2006; accepted 27 November 2006 Abstract The control of ethylene in stored environments plays a key role in prolonging the postharvest life of many fresh produce types. However, there has been a paucity of research in recent years on developing novel and more effective ethylene scavenging materials. In this study a palladium (Pd)- promoted powdered material that has significant ethylene adsorption capacity (4162 Lg 1 material) at 20 C and approximately 100% RH was identified and was shown to be far superior to KMnO 4 -based scavengers when used in low amounts and in conditions of high relative humidity (RH). Initial screening was carried out in a plug flow reactor with 200 LL 1 ethylene, 10% (v/v) O 2 balanced with He at approximately 100% RH. Further work demonstrated that the Pd-promoted material at either 0.01 or 0.03 g L 1 effectively scavenged both exogenously administered (100 LL 1 ) and/or endogenously produced ethylene by banana or avocado, respectively, to sub- LL 1 concentrations within a 24 h period. Optimum ethylene adsorption capacity was calculated as approximately 10,000 Lg 1. Accordingly, corresponding inhibition of ethylene-induced ripening was observed. When removed, Pd-material did not disrupt subsequent ripening. The results from this study demonstrate that Pd-promoted material has commercial potential Elsevier B.V. All rights reserved. Keywords: Avocado; Banana; Ethylene adsorption capacity; Strawberry 1. Introduction The removal of ethylene and/or inhibition of the effect of ethylene in stored environments is fundamental to maintaining postharvest quality of climacteric produce (Saltveit, 1999). In recent years, however, there has been a paucity of research on developing new and more efficacious ethylene scrubbing materials. In contrast, there has been an exponential increase in research using the ethylene binding inhibitor 1-methylcyclopropene (1-MCP; Watkins, 2006). Thus, research activity has drifted away from ethylene removal to preventing the actions of ethylene through using 1-MCP. Despite various ethylene scrubbing technologies being available (e.g. high temperature catalytic degradation, activated carbon, etc.) most commercial ethylene control systems rely on both adequate ventilation (often periodic) and oxidation of ethylene using potassium permanganate (KMnO 4 )-based mechanisms. Ventilation, however, is not appropriate in sealed environments (e.g. controlled atmosphere or some packaging Corresponding author. Tel.: ; fax: address: l.a.terry@cranfield.ac.uk (L.A. Terry). formats) or where precise ethylene control is required. KMnO 4 supported on activated alumina spheres has limited long-term efficacy in environments with high relative humidity (e.g. cold stores). The present study details the efficacy of a new palladium (Pd)-promoted material to remove ethylene and hence control ethylene-induced ripening for climacteric (viz. banana and avocado) fruit. In addition, a trial was conducted to investigate the effect of ethylene removal on postharvest strawberry fruit quality. 2. Materials and methods 2.1. Preliminary experiments Initial screening of candidate samples was conducted to determine the ethylene adsorption capacity of the newly discovered Pd-promoted material. The chosen material consisted of a Pd-impregnated zeolite giving finely dispersed Pd particles. Metal loading was 2.5% Pd (m/m). Measurements were carried out using a synthetic gas mixture at room temperature (21 C) in a plug flow reactor using 0.1 g of active material in a gas composition of 200 LL 1 ethylene, 10% (v/v) O 2 balanced with He at approximately 100% relative /$ see front matter 2007 Elsevier B.V. All rights reserved. doi: /j.postharvbio

2 2 L.A. Terry et al. / Postharvest Biology and Technology xxx (2007) xxx xxx humidity at a flow rate of 50 ml min 1. Humidity was introduced by passing the reactant gas (minus ethylene component) through a water saturator at 21 C. The material was evaluated against other ethylene scavengers reported in the literature including KMnO 4 supported on a high surface area alumina (5%, m/m; KMnO 4 /Al 2 O 3). Reactor outlet gas concentrations were analysed using a Thermo Onix ProLab mass spectrometer (Thermo Onix, TX) using mass/charge ratios of 26 and 44 for ethylene and CO 2, respectively. Ethylene uptake capacity was measured using a simple breakthrough measurement in which the total integrated ethylene removal was determined after the outlet ethylene concentration from the reactor had reached the inlet ethylene concentration showing that the scavenger was saturated with ethylene. Further experiments were carried out at room temperature in an unstirred batch reactor (0.86 L) with 0.1 g active material and an initial gas composition of 550 LL 1 ethylene, 40% (v/v) air balanced with Ar. Selected gas concentrations were measured at hourly intervals with a Varian CP-4900 Micro GC (Varian Inc., CA). Gas samples (40 ms duration) were taken via an automated recirculating sampling system. Column and injector temperatures were set at 60 and 70 C, respectively. The 0.15 mm diameter, 10 m long column was packed with PoraPLOT Q. Ethylene and CO 2 were calibrated against 10 LL 1 ethylene balanced with air and 5% (v/v) CO 2 balanced with Ar (Air Products Europe, Surrey, UK). A thermal conductivity detector was used with He carrier gas at 276 kpa inlet pressure. Peak integration was carried out within the Varian STAR software Plant material and experimental set-up The efficacy of Pd-promoted material to retard ethyleneinduced ripening in banana and avocado and to reduce senescence in strawberry was tested Banana Mature pre-climacteric banana (Musa spp. AAA group, Cavendish sub-group) fruit (n = 108) originating from Costa Rica were purchased from a banana importer (S.H. Pratt Co. Ltd., Bedfordshire, UK) and stored overnight at 14 C. Fruit arrived in UK on 20 February 2006 and were transported to the laboratory. The following day fruit were cut into individual fingers (mean finger length of 14 cm) with a sharp knife and completely randomized. Fruit were left for 1h to allow for the exudation of latex from the cut surface to seize. Fruit (n = 3) were held in the dark at 16 C in 3 L airtight glass jars (n = 36) for 3 days containing powdered Pd-promoted material placed in weighing boats (Experiment 1: mg; Experiment 2: 0 50 mg). Jars were then treated with or without exogenous ethylene (100 LL 1 ; SIP Analytical Ltd., Kent, UK). After 3 days storage, fruit were removed from jars and kept on open trays at 18 C for a further 4 6 days. Effect of treatments (n = 12) on ethylene and CO 2 concentration was recorded daily over the first 3 days. Objective colour change of fruit was recorded at regular intervals throughout both experiments Avocado Early season pre-climacteric avocado (Persea americana) cv. Hass fruit (n = 72), originating from Navobani Boerdery and imported through Westfalia Marketing (Tzaneen, LP, South Africa), were supplied by a tropical fruit supplier (Minor, Weir and Willis Ltd., Birmingham, UK) and stored overnight at 12 C. Fruit were packed on 4 May 2006 and received in the UK on 31 May On arrival at the laboratory, fruit were 32-daysold, which is not unusual for avocado fruit being imported into the UK. Fruit were not pre-treated with 1-MCP. Fruit (n =2) were held in the dark at 12 C within 3 L sealed jars (n = 36) for 3 days, which were initially treated with or without ethylene (100 LL 1 ), and contained 0, 100 or 1000 mg of powdered Pd-promoted material or powdered Ethysorb, respectively. An additional treatment was also used, whereby fruit were treated with or without ethylene as before, but then after one day 1000 mg Pd-promoted material was put into jars. Fruit were removed after 3 days to avoid CO 2 poisoning and kept on open trays at 12 C for a further 7 days. Effect of treatments (n = 12) on ethylene, and CO 2 concentrations was recorded over 3 days. Objective colour change of fruit and firmness was recorded at regular intervals Strawberry Early season glasshouse-grown strawberry (Fragaria ananassa) cv. Kimberley fruit (n = 360), were purchased from a commercial grower (Polehouse Nurseries, Essex, UK). Fully ripened red stage fruit were harvested in the morning and transported back to the laboratory within 2 h on 2 May Fruit (n = 10) were held at 5 C in the dark within 3 L sealed jars (n = 36) for 3 days, which were initially treated with or without 100 LL 1 ethylene, and contained 0 50 mg powdered Pd-promoted material as described before. Fruit were removed after 3 days and kept in the dark in closed, but vented, plastic punnets at 5 C for a further 10 days. Effect of treatments (n = 12) on ethylene, and CO 2 concentrations was recorded over 3 days. Objective colour change of fruit and calyx was recorded at regular intervals over 13 days. All fruit remained free from disease during the experiment Ethylene and CO 2 quantification Gas samples from 3 L jars were removed with repeated full withdrawal-injection displacements of a 20 ml plastic syringe. Ethylene concentration was quantified using a GC8340 gas chromatograph (Carlo Erba Instruments, Herts., UK) fitted with an EL 980 FID and DP800 integrator (Thermoquest, Herts., UK). Oven and detector temperatures were set at 100 C. The 2 m long stainless steel column was packed with Porapak P mesh range (Jones Chromatography, Mid Glamorgan, UK). Ethylene was calibrated against 10.6 LL 1 ethylene balanced in N 2 (British Oxygen Company (BOC) Gases, Surrey, UK). CO 2 was quantified using the same GC system with hot wire detection (Budu and Joyce, 2003). The hot wire detector was operated at 120 C and the oven at 80 C. The 2 m long 4mm column was packed with mesh size Porapak Q (Jones

3 L.A. Terry et al. / Postharvest Biology and Technology xxx (2007) xxx xxx 3 Chromatography). The GC was calibrated with 10.3% (v/v) CO 2 in N 2 (BOC) Colour measurements The objective colour of each fruit was measured at regular intervals during storage using a Minolta DP-400 colorimeter (Minolta Co. Ltd., Japan) with an 8 mm light path aperture. The instrument was calibrated with a Minolta standard white tile CR-400 (Y = 93.5, x = , y = ). The mean of three readings at three equidistant points (n = 9) along the same lateral surface for banana or around the equatorial axis for avocado and strawberry was recorded and the lightness (L*), chroma (colour saturation; C*) and hue angle (H ) automatically calculated. The change in calyx colour was also measured, by placing the Minolta head over the middle section of the calyx (n = 3) Firmness Fig. 1. Ethylene breakthrough measurement on Pd-promoted material held in humid conditions. Avocado fruit firmness was measured on opposite sides of peeled fruit using an Instron Universal Testing Machine (Model 1122, Bucks., UK) fitted with a flat-head 8 mm probe. Crosshead speed was set at 20 mm min 1. Firmness was expressed as the maximal force (N) required for tissue failure Statistical analysis All statistical analyses were carried out using Genstat for Windows Version (VSN International Ltd., Herts., UK). Least significant difference values (LSD; P = 0.05) were calculated for mean separation using critical values of t for two-tailed tests. 3. Results 3.1. Preliminary experiments with synthetic ethylene gas After screening a range of different materials on a plug flow reactor, one Pd-promoted material was identified as having considerable ethylene adsorption capacity at room temperature. The Pd-promoted material typically removed all measurable ethylene until breakthrough occurred (Fig. 1). The plug flow reactor experiments demonstrated that the Pd-promoted mate- Fig. 2. Effect of Pd-promoted material on gaseous composition (carbon dioxide, ( ); ethylene, ( ); ethane, ( ) within sealed jars, initially containing 550 LL 1 ethylene in air. rial outperformed KMnO 4 by having an approximately 6-fold higher ethylene adsorption capacity; typically 4162 Lg 1 under approximately 100% RH. This performance was increased to 45,600 Lg 1 under dry conditions (low %RH), thus, representing a 60-fold higher activity than KMnO 4. All ethylene adsorption capacity was lost when KMnO 4 was pre-treated with Table 1 Ethylene concentration ( LL 1 ) within 3 L sealed jars (n = 36) containing pre-climacteric banana cv. Cavendish fruit (n = 3) held in the presence of Pd-promoted material ( mg) Pd-promoted material (mg) Ethylene concentration ( LL 1 ) (0.00) (0.04) (0.05) (0.05) (0.00) (0.09) (0.07) (0.05) (0.00) (0.03) (0.25) (0.01) (0.00) 0.00 (0.00) 0.00 (0.01) 0.00 (0.01) (0.00) 0.00 (0.04) 0.00 (0.08) 0.00 (0.00) (0.00) 0.00 (0.00) 0.00 (0.00) 0.00 (0.00) Jars were initially treated with or (without) 100 LL 1 ethylene. LSD (P = 0.05) =

4 4 L.A. Terry et al. / Postharvest Biology and Technology xxx (2007) xxx xxx Table 2 Ethylene concentration ( LL 1 ) within 3 L sealed jars (n = 36) containing pre-climacteric banana cv. Cavendish fruit (n = 3) held in the presence of Pd-promoted material (0 50 mg) Pd-promoted material (mg) Ethylene concentration ( LL 1 ) (0.00) (0.14) (0.13) (0.12) (0.00) (0.02) (0.01) (0.00) (0.00) (0.00) (0.00) 6.86 (0.00) (0.00) 0.85 (0.00) 0.00 (0.00) 0.00 (0.00) (0.00) 0.00 (0.00) 0.00 (0.00) 0.00 (0.00) (0.00) 0.00 (0.16) 0.00 (0.06) 0.00 (0.03) Jars were initially treated with or (without) 100 LL 1 ethylene. LSD (P = 0.05) = Table 3 CO 2 concentration (%) within 3 L sealed jars (n = 36) containing pre-climacteric banana cv. Cavendish fruit (n = 3) held in the presence of Pd-promoted material ( mg) Table 4 CO 2 concentration (%) within 3 L sealed jars (n = 36) containing pre-climacteric banana cv. Cavendish fruit (n = 3) held in the presence of Pd-promoted material (0 50 mg) Pd-promoted material (mg) CO 2 concentration (%) Pd-promoted material (mg) CO 2 concentration (%) (2.02) 6.49 (3.61) (5.23) (1.87) 5.95 (3.08) (4.21) (2.00) 6.07 (3.32) (4.58) (1.94) 4.63 (3.33) 6.50 (4.72) (2.24) 4.85 (3.68) 6.82 (5.10) (2.14) 3.94 (3.66) 5.45 (5.09) (1.46) 5.60 (3.18) (4.81) (1.49) 5.30 (3.73) (3.85) (1.58) 5.41 (3.73) (3.85) (1.57) 5.78 (2.81) 9.77 (4.00) (1.65) 5.46 (3.00) 8.29 (4.29) (1.73) 4.79 (2.97) 6.79 (4.43) Jars were initially treated with or (without) 100 LL 1 (P = 0.05) = ethylene. LSD Jars were initially treated with or (without) 100 LL 1 (P = 0.05) = ethylene. LSD 100% RH for 72 h at 21 C prior to analysis (data not shown). The loss in performance of the KMnO 4 -based material appeared to be due to conversion of the KMnO 4 to manganese oxide judging from the change in colour of the material from purple to brown. A small amount of Pd-promoted material (0.1 g) was sufficient to totally remove 550 LL 1 ethylene in air mixture within 2h (Fig. 2). Some ethane (65 LL 1 ) production and a slight rise in CO 2 concentration were also observed (Fig. 2), indicating that some of the ethylene was reacting over the Pd-promoted material. However, these products represent only approximately 16% of the total carbon balance present in the container used, suggesting that most of the ethylene was adsorbed on the Pdpromoted material Banana Exogenous ethylene concentration was significantly (P < 0.001) reduced with increasing amount of Pd-promoted material (Tables 1 and 2), and from preliminary work it is likely that ethylene was removed within a few hours of application. The efficacy threshold was determined as 30 mg of Pd-promoted material in 3 L (0.01 g L 1 ; ethylene adsorption capacity approximately 10,000 Lg 1 ) to reduce 100 LL 1 ethylene to sub-physiologically active levels for pre-climacteric banana cv. Cavendish fruit. Accordingly, where ethylene had been reduced below physiologically active levels the climacteric-induced increase in respiration (CO 2 concentration; Tables 3 and 4) and associated objective colour change Table 5 Ethylene concentration ( LL 1 ) within 3 L sealed jars (n = 36) containing pre-climacteric avocado cv. Hass fruit (n = 2) held in the presence of Pd-promoted material (0, 100, and 1000 mg) or Ethysorb (100 and 1000 mg) Material (mg) Ethylene concentration ( LL 1 ) Control (0.00) (0.69) (1.57) (3.74) 100 Pd-promoted (0.00) 0.00 (0.07) 0.00 (0.06) 0.00 (0.04) 1000 Pd-promoted (0.00) 0.00 (0.00) 0.00 (0.01) 0.00 (0.00) 1000 * Pd-promoted (0.00) (0.24) 0.00 (0.14) 0.00 (0.12) 100 Ethysorb (0.00) (0.18) (0.21) (0.10) 1000 Ethysorb (0.00) 0.07 (0.54) 0.21 (0.24) 0.02 (0.10) Jars were initially treated with or (without) 100 LL 1 ethylene. * Pd-promoted material (1000 mg) was put in jars after day 1 after fruit had been treated with or without 100 LL 1 ethylene. LSD (P = 0.05) =

5 L.A. Terry et al. / Postharvest Biology and Technology xxx (2007) xxx xxx 5 with ethylene (100 LL 1 ) the climacteric was initiated as normal (data not shown) demonstrating that Pd-promoted material had no detrimental effect on subsequent fruit quality. No abnormal or uneven degreening was observed Avocado Fig. 3. (A C) Effect of Pd-promoted material (0, ( ); 10, ( ); 20, ( ); 30, ( ); 40, ( ); 50, ( )) on change in L*, C* and H of pre-climacteric banana cv. Cavendish fruit held at 16 C within 3 L sealed jars for 3 days which were initially treated with 100 LL 1 ethylene. Fruit were removed and kept at 18 C for 6 days. LSDs (P = 0.05) for A, B and C = 2.108, and 1.547, respectively. * Differences between treatments were minimal for fruit which received no ethylene (data not shown). (Fig. 3A C) from green to yellow was not observed. This remarkable efficacy suggests that only very small amounts of Pd-promoted material are required to ensure that ethylene is below physiologically active levels for climacteric fruit. When bananas, which had previously been held in jars in the presence of Pd-promoted material (>30 mg), were subsequently treated Exogenous and endogenous ethylene concentration was reduced significantly (P < 0.001) with increasing amount of Pdpromoted material (Table 5). Pd-promoted material (100 mg) was approximately 50-fold more effective at reducing exogenous ethylene than Ethysorb (100 mg). In the presence of Pd-promoted material, ethylene was reduced to subphysiologically active levels as demonstrated by maintenance of firmness (P = 0.004) after 7 days. Firmness of fruit previously treated with ethylene (100 LL 1 ) and held in the presence of 100 or 1000 mg Pd-promoted material was and N versus 13.0 and 12.0 N for control and Ethysorb (100 mg)- treated fruit, respectively. However, there was no significant effect (P > 0.05) caused by the presence of Pd-promoted material on CO 2 concentration over time (data not shown) and thus, the reduction in ethylene caused by the presence of Pd-promoted material had no effect on respiration for the first 3 days. CO 2 concentrations rose from 5.10 to 13.23% between days 1 and 3, respectively. Internal fruit colouration was not affected by presence/absence of ethylene (data not shown). The overall visual colour change of avocado cv. Hass fruit was also affected by ethylene and thus presence/absence of Pdpromoted material. Fruit held in the presence of 100 or 1000 mg Pd-promoted material for 3 days were generally greener, and thus less ripe, than control fruit after 7 10 days (data not shown). The colour of 10 day-old fruit previously treated with ethylene (100 LL 1 ) and held in the presence of 100 mg Pd-promoted material was 90.8 H as compared against 53.1 and 72.4 H for control and Ethysorb (100 mg)-treated fruit, respectively. This said, there was no significant difference (P > 0.05) in objective colour measurements between treatments when assessed using objective point data measurement (n = 3) of fruit (n = 9) around the equatorial axis. The sampling method used for objective colour measurement, therefore, was unable to account for the heterogeneity in colour distribution commonly associated with avocado cv. Hass fruit and did not reflect that observed by eye. When fruit were treated with ethylene and then subsequently held in the presence of Pd-promoted material (1000 mg) after day 1, ethylene was reduced to sub-physiologically active levels (Table 5). Despite the climacteric being initiated for these fruit, subsequent total removal of ethylene resulted in better maintenance of fruit firmness than controls and thus, disruption of the normal and expected climacteric respiratory rise. Therefore, for the first time an ethylene scavenger has been shown to be capable of extending shelf-life even when the climacteric respiratory rise has been initiated Strawberry Exogenous ethylene concentration was significantly (P < 0.001) reduced with increasing amount of Pd-promoted

6 6 L.A. Terry et al. / Postharvest Biology and Technology xxx (2007) xxx xxx Table 6 Ethylene concentration ( LL 1 ) within 3 L sealed jars (n = 36) containing strawberry cv. Kimberley fruit (n = 10) held in the presence of Pd-promoted material (0 50 mg) Pd-promoted material (mg) Ethylene concentration ( LL 1 ) (0.00) (0.15) (0.03) (0.07) (0.00) (0.06) (0.15) (0.03) (0.00) (0.00) (0.02) (0.00) (0.00) (0.00) 7.40 (0.02) 2.70 (0.02) (0.00) 7.17 (0.10) 2.84 (0.02) 0.75 (0.02) (0.00) 0.10 (0.94) 0.03 (0.00) 0.05 (0.00) Jars were initially treated with or (without) 100 LL 1 ethylene. LSD (P = 0.05) = material (Table 6). However, there was no significant effect (P > 0.05) of the presence of Pd-promoted material on CO 2 concentration over time (data not shown) and thus, the reduction in ethylene concentration (sub- LL 1 ) caused by the presence of Pd-promoted material had no effect on respiration of strawberry fruit. CO 2 concentrations increased to approximately 3% after 3 days storage at 5 C. There was generally no significant effect of presence/absence of ethylene on colour change of calyx or fruit. However, the presence of Pd-promoted material did maintain calyx greenness (data not shown) and fruit colour (H angle; data not shown). Although significant effects (P < 0.001) were observed these differences were not really discernable by eye and, thus, not of commercial value. The reduction in exogenous ethylene had no effect on disease incidence. 4. Discussion For effective long-distance transport and subsequent storage many climacteric fruit need to be held in a low (sub LL 1 ) ethylene environment. Control of the effects of ethylene in stored environments has tended in recent times to have drifted away from ethylene removal to preventing the actions of ethylene using 1-MCP. The reasons for this are varied, but probably have resulted from not only 1-MCP being highly effective at blocking ethylene perception, but also there being a lack of commercially available ethylene scavengers that are sufficiently efficacious at removing ethylene for extended periods in environments with high RH% (e.g. holding chambers, packaging, etc.). The Pd-promoted material, like 1-MCP, can be used to control ripening; however, the mechanism by which this is achieved is fundamentality different. Rather than blocking the perception of ethylene, the Pd-promoted material effectively removes ethylene rapidly from an environment, and thus there is less risk that unwanted side-effects occur. This said, for ethylene scavengers to work effectively there is a requirement for them to be in the presence of the commodity. Although the benefits of using 1-MCP are generally positive for many climacteric fruit (Watkins, 2006), it has been shown that 1-MCP is not applicable for all climacteric fresh produce types as it may disrupt normal ripening. The effectiveness of 1- MCP to inhibit ripening in climacteric fruit is not only a function of the amount and duration of 1-MCP applied being sufficient to saturate ethylene binding sites, but is also that the fruit may recover from 1-MCP-induced inhibition to allow normal ripening to take place when required (Watkins, 2006). The persistence of inhibition of ethylene production caused by 1-MCP can be variable. 1-MCP has also been shown to have differential adsorption for different fruit (Dauny et al., 2003) and be depleted by various non-target materials in storage environments (e.g. moistened cardboard; Vallejo and Beaudry, 2006). Incomplete and uneven peel degreening was a feature of mature green banana (Cavendish cv. Williams) fruit treated with 1-MCP (Harris et al., 2000; Macnish et al., 2000), even in the presence of propylene (Golding et al., 1998). However, in the present study, no disruption of ripening was observed for banana fruit (Fig. 3) which were treated with 100 LL 1 ethylene after being held previously for 3 days in the presence of Pd-promoted material (0.01 g L 1 ) and thus in an ethylene-free environment (Tables 1 and 2). For avocado cv. Hass fruit, complete ethylene removal using Pd-promoted material was generally more effective as compared to control and Ethysorb in slowing down ripening (Table 5). Likewise, 1-MCP has also been shown to extend storage life of avocado (Feng et al., 2000; Jeong et al., 2003; Adkins et al., 2005; Hershkovitz et al., 2005; Woolf et al., 2005). Presence of Pdpromoted material delayed ethylene-induced softening. Equally, ripening of avocado cv. Hass fruit was also delayed by applying 1-MCP (0.5 LL 1 ) h after ethylene (100 LL 1 ) treatment (Adkins et al., 2005). The capacity to delay ripening using Pd-promoted material (1000 mg) after ethylene (100 LL 1 ) treatment was also demonstrated in the present study. There is little commercial benefit of using Pd-promoted material for strawberry. Even though ethylene was removed using the Pd-promoted material (Table 6) the effects on postharvest strawberry fruit quality and storage life were small and of little tangible worth. A similar conclusion was given by Bower et al. (2003) who concluded that despite some beneficial effects neither the removal of ethylene or treatment with 1-MCP were likely to be cost-effective methods of extending the storage life of strawberries (cv. not stated). Again, these results mirror those reported by many other authors that the effects of ethylene are not well defined for strawberry and may be affected by cultivar, maturity, storage temperature and even tissue type (Jiang et al., 2001; Bower et al., 2003; Iannetta et al., 2006). Siriphanich (1980) found no difference between strawberry fruit held in air or 100 LL 1 ethylene. 5. Conclusion The current study has demonstrated for the first time that presence of a Pd-promoted material was effective at reducing ethylene to sub-physiological active levels at approximately 0.01 g L 1 (ethylene adsorption capacity approximately 10,000 Lg 1 ) when used for only 3 days on pre-climacteric green banana and at approximately 0.03 g L 1 when again used for only 3 days on pre-climacteric green avocado cv. Hass fruit. The efficacy of Pd-promoted material was far superior to KMnO 4 when used in low amounts and especially at high RH%.

7 L.A. Terry et al. / Postharvest Biology and Technology xxx (2007) xxx xxx 7 The results from this study demonstrate that Pd-promoted material has potential to be used commercially. Future research will further elucidate the optimum concentrations, timing of application and format to extend postharvest life of avocado and other climacteric fresh produce types. If optimised there remains the possibility of the Pd-promoted material being used to extend shelf-life of climacteric fruit even when the climacteric respiratory rise has been just initiated as demonstrated for avocado cv. Hass fruit. Acknowledgments The authors thank Mr. A.J. Hilton and Mrs. B. Cook for technical assistance, Minor Weir and Willis Ltd., for supply of avocado fruit and Anglo Platinum for financial support. References Adkins, M.A., Hofman, P.J., Stubbings, B.A., Macnish, A.J., Manipulating avocado fruit ripening with 1-methylcyclopropene. Postharvest Biol. Technol. 35, Bower, J.H., Biasi, W.V., Mitcham, E.J., Effects of ethylene and 1-MCP on the quality and storage life of strawberries. Postharvest Biol. Technol. 28, Budu, A.S., Joyce, D.C., Effect of 1-methylcyclopropene on the quality of minimally processed pineapple fruit. Aust. J. Exp. Agric. 43, Dauny, P.T., Joyce, D.C., Gambay, C., Methylcyclopropene influx and efflux in Cox apple and Hass avocado fruit. Postharvest Biol. Technol. 29, Feng, X.Q., Apelbaum, A., Sisler, E.C., Goren, R., Control of ethylene responses in avocado fruit with methylcyclopropene. Postharvest Biol. Technol. 20, Golding, J.B., Shearer, D., Wyllie, S.G., McGlasson, W.B., Application of 1-MCP and propylene to identify ethylene-dependent ripening processes in mature banana fruit. Postharvest Biol. Technol. 14, Harris, D.R., Seberry, J.A., Wills, R.B.H., Spohr, L.J., Effect of fruit maturity on efficiency of 1-methylcyclopropene to delay the ripening of bananas. Postharvest Biol. Technol. 20, Hershkovitz, V., Saguy, S.I., Pesis, E., Postharvest application of 1-MCP to improve the quality of various avocado cultivars. Postharvest Biol. Technol. 37, Iannetta, P.P.M., Laarhoven, L.J., Medina-Escobar, N., James, E.K., McManus, M.T., Davies, H.V., Harren, F.J.M., Ethylene and carbon dioxide production by developing strawberries show a correlative pattern that is indicative of ripening climacteric fruit. Physiol. Plant. 127, Jeong, H., Huber, D.J., Sargent, S.A., Delay of avocado (Persea americana) fruit ripening by 1-methylcyclopropene and wax treatments. Postharvest Biol. Technol. 28, Jiang, Y., Joyce, D.C., Terry, L.A., Methylcyclopropene treatment affects strawberry fruit decay. Postharvest Biol. Technol. 23, Macnish, A.J., Joyce, D.C., Hofman, P.J., Simons, D.H., Reid, M.S., Methylcyclopropene treatment efficacy in preventing ethylene perception in banana fruit and grevillea and waxflower flowers. Aust. J. Exp. Agric. 40, Saltveit, M.E., Effect of ethylene on quality of fresh fruits and vegetables. Postharvest Biol. Technol. 15, Siriphanich, J., Postharvest Deterioration of Strawberries as Influenced by Ethylene and Some Other Volatiles. University of California, Davis. Vallejo, F., Beaudry, R., Depletion of 1-MCP by non-target materials from fruit storage facilities. Postharvest Biol. Technol. 40, Watkins, C.B., The use of 1-methylcyclopropene (1-MCP) on fruits and vegetables. Biotechnol. Adv. 24, Woolf, A.B., Requejo-Tapia, C., Cox, K.A., Jackman, R.C., Gunson, A., Lu Arpaia, M., White, A., MCP reduces physiological storage disorders of Hass avocados. Postharvest Biol. Technol. 35,