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1-MCP efficacy in extending storage life of ‘Bartlett’ pears is affected by harvest maturity, production elevation, and holding temperature during treatment delay
Postharvest Biology and Technology 103 (2015) 1–8
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1-MCP efficacy in extending storage life of ‘Bartlett’ pears is affected by harvest maturity, production elevation, and holding temperature during treatment delay Yan Wang a, * , David Sugar b a Department of Horticulture, Oregon State University, Mid-Columbia Agricultural Research and Extension Center, 3005 Experiment Station Dr., Hood River, OR 97031, USA b Oregon State University, Southern Oregon Research and Extension Center, 569 Hanley Rd., Medford, OR 97502,USA
A R T I C L E I N F O
A B S T R A C T
Article history: Received 26 October 2014 Received in revised form 24 February 2015 Accepted 25 February 2015
The efficacy of 1-methylcyclopropene (1-MCP) in extending storage life of the Pacific Northwest ‘Bartlett’ pear is inconsistent. The effects of harvest maturity [H1: flesh firmness (FF) 83.6 N; H2: FF 74.8 N], production elevation (E1 150 m; E2 610 m), and holding temperature (0 and 5 C) prior to application of 1-MCP have been measured with respect to ethylene production, fruit quality, and storage disorders of ‘Bartlett’ fruit during 6 months of storage at 1.1 C. 1-MCP at 0.3 mL L 1 for 24 h at 0 C inhibited ethylene production, FF and green color losses, senescence disorders, and friction discoloration for H1 fruit from both elevations. However, 1-MCP efficacy was reduced moderately in E1H2 fruit and reduced to a greater extend in E2H2 fruit. Internal ethylene concentration (IEC) at harvest was not detected in H1 fruit from either elevation, but it accumulated in E1H2 and E2H2 fruit (E2H2 > E1H2). The holding temperature at 5 C but not 0 C for 12 d between harvest and 1-MCP treatment increased fruit IEC and ethylene production rate and reduced the fruit response to subsequent 1-MCP treatment. The fruit physiological stage at the moment of 1-MCP treatment determined the efficacy of 1-MCP in extending the storage life of ‘Bartlett’ pears. 1-MCP retarded development of ripening capacity and 10–14 d at 20 C were needed to ripen 1-MCP treated ‘Bartlett’ pears to optimum eating quality following 5–6 months of cold storage. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Pyrus communis 1-MCP Harvest maturity Production elevation Delayed application Storage disorders Ripening capacity
1. Introduction In the U.S. Pacific Northwest (PNW), ‘Bartlett’ pears are normally stored for 1–3 months in regular air (RA) or 3–5 months in controlled atmosphere (CA) storage at 1.1 C (Wang and Sugar, 2013). ‘Bartlett’ pear storage life is often shortened and significant losses may occur after long-term storage or long-distant shipping due to senescence disorders such as yellowing, senescent scald (SS) and senescent core breakdown (SCB) (Ju et al., 2001; VillalobosAcuña et al., 2011a). A portion of ‘Bartlett’ pear production in the PNW is stored in field bins, and friction discoloration (FD) can occur during packing after storage. In recent years, a trend of moving from cannery to fresh market has increased the need to extend ‘Bartlett’ storage life to prolong the packing and marketing seasons. Development of the storage disorders and a relatively short storage life of ‘Bartlett’ pear are associated with increased ethylene
* Corresponding author. Tel.: +1 541 386 2030; fax: +1 541 386 1905. E-mail address: [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.postharvbio.2015.02.013 0925-5214/ ã 2015 Elsevier B.V. All rights reserved.
production induced by cold storage (Ekman et al., 2004; VillalobosAcuña et al., 2011a). 1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor that delays senescence and ripening of many fruit, including European pears, through irreversible binding to ethylene receptors of fruit cells (Sisler and Serek, 1997; Watkins, 2006). 1-MCP inhibits ethylene production and eliminates or reduces SS and SCB of ‘Bartlett’ pear after cold storage (Bai et al., 2006; Calvo and Sozzi, 2009; DeEll and Ehsani-Moghaddam, 2011; Ekman et al., 2004; Trinchero et al., 2004; Villalobos-Acuña et al., 2011a,b). European pears (Pyrus communis) are enjoyed by consumers when fruit have ripened to a buttery and juicy texture at warm temperatures following cold storage (Chen, 2004; Xie et al., 2014). The response of European pears to 1-MCP is affected by application conditions such as 1-MCP concentration, exposure duration, exposure temperature, and presence of exogenous ethylene in the treating room (Argenta et al., 2003; Chen and Spotts, 2005; DeEll et al., 2002; Ekman et al., 2004; Villalobos-Acuña et al., 2011b). 1-MCP at higher rates can eliminate the ripening capacity of European pears (Chen and Spotts, 2005; Bai et al., 2006). To balance between reducing senescence disorders and the recovery of ripening capacity after cold storage, recommended 1-MCP
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treatment for ‘Bartlett’ pears is 0.3 mL L 1 for 24 h. Recent studies in our laboratory indicate that if temperatures of 10–20 C occur during a 24 h 1-MCP treatment yellowing of ‘Bartlett’ pears is accelerated during subsequent storage at 1.1 C. While the pear industry is highly interested in commercializing 1-MCP to extend the packing season and reduce storage and shipping losses of ‘Bartlett’, its efficacy is found to be quite variable during commercial application in the PNW (industry communication). It was also reported that in many cases no response was seen or that a much higher concentration of 1-MCP was required to have an effect on ‘Bartlett’ in commercial applications in California (Villalobos-Acuña et al., 2011b). It is known that factors such as fruit maturity at the time of treatment, application delay after harvest, and production lot affect 1-MCP efficacy on different fruit (Mir et al., 2001; Villalobos-Acuña et al., 2011a,b; Watkins and Nock, 2005; Zhang et al., 2009). In the PNW, ‘Bartlett’ pears are harvested when flesh firmness (FF) declines to between 83.6 and 74.8 N (Chen, 2004). A storage room is often filled with ‘Bartlett’ fruit from a range of production elevations and it may take 12 d to fill a storage room before it is ready for 1-MCP treatment. The commercial harvest maturity, production elevation, and holding temperature during the period of room filling may affect fruit ethylene synthesis, therefore the response degree of fruit to 1-MCP. The objective of this study was to determine the effects of early/late commercial harvest maturity (83.6/74.8 N), lower/higher production elevation (150/600 m) in the mid-Columbia area, and holding temperature (0 and 5 C) during a 12 d delay between harvest and 1-MCP treatment on 1-MCP efficacy with respect to ethylene production, storage disorders, and ripening capacity of ‘Bartlett’ pears during subsequent 6 months of storage at 1.1 C. 2. Materials and methods
sample was injected into a gas chromatograph (Shimadzu GC-8A, Kyoto, Japan). Nitrogen was used as the carrier gas at a flow rate of 0.8 mL s 1. The injector and detector port temperatures were 90 and 140 C, respectively. An external standard of ethylene (1.0 mL L 1) was used for calibration. The limit of ethylene detection was approximately 0.08 mL L 1. Ethylene production and CO2 production rates were measured by incubating five fruit per replicate in a 3.8 L airtight jar for 1 h at 20 C. Gas samples were withdrawn through a septum on the top using a 1 mL gas-tight syringe. Ethylene was measured with the same GC system used for IEC determination. Ethylene production rate was expressed as ng kg 1 s 1. The headspace CO2 concentration was measured using an O2 and CO2 analyzer (Model 900161, Bridge Analyzers Inc., Alameda, CA, USA). Fruit respiration rate was expressed as mg CO2 kg 1 s 1. 2.1.3. Fruit storage quality Fruit quality was measured on 10 fruit of each replicate. Peel chlorophyll content was estimated using a DA meter (Sinteleia, Bolonga, Italy) and expressed as IAD value (Ziosi et al., 2008). Measurements were taken on opposite sides of the equator of each fruit. After color determination, FF was measured using a fruit texture analyzer (model GS-14, Guss Manufacturing Ltd., Strand, South Africa) with an 8 mm probe that penetrates 9 mm in 0.9 s. Two measurements were obtained per fruit on opposite sides of the equator after removal of 20 mm diameter peel discs. After chlorophyll and FF determination, flesh tissue of 0.1 kg was ground for 3 min in a juice extractor (Acme Model 6001) equipped with a uniform strip of milk filter. Titratable acidity (TA) was determined by titrating 10 mL of the juice to pH 8.1 using 0.1 N NaOH with a commercial titration system (Model T80/20, Schott-Gerate, Hofheim, Germany) and expressed as meq L 1 of juice. Soluble solid content (SSC) was determined using a hand held refractometer (Atago, Tokyo, Japan) and expressed as a percentage.
2.1. Harvest maturity and production elevation study 2.1.1. Fruit materials and 1-MCP treatment ‘Bartlett’ pears were harvested at FF of 84.5 (H1) and 76.1 N (H2) from the orchard at Oregon State University’s Mid-Columbia Agricultural Research and Extension Center (MCAREC) in Hood River, OR, USA (45.7 N, 121.5 W, elevation 150 m) and labeled as E1. ‘Bartlett’ fruit were also harvested at FF of 83.2 (H1) and 75.6 N (H2) from an orchard in Parkdale, OR, USA (45.5 N, 121.6 W, elevation 610 m) and labeled as E2. Defect-free fruit were randomly packed in 48 wooden boxes (80 fruit per box) with standard perforated polyethylene liners and were cooled overnight at 0 C. On the second day, half of the fruit in each group (E1H1, E1H2, E2H1, E2H2) were exposed to 0.3 mL L 1. 1-MCP released from SmartFresh1 tabs provided by AgroFresh (Springhouse, PA, USA) in an airtight room (39.75 m3) with a circulation fan at 0 C for 24 h. Fruit of the other half were held at 0 C as untreated control. Following 1-MCP treatment, fruit with or without 1-MCP treatment were then stored at 1.1 C in air for 6 months. Fruit maturity attributes: FF, fruit color, and internal ethylene concentration (IEC) were determined immediately after harvest on E1H1, E1H2, E2H1, and E2H2 fruit. The control and 1-MCP treated fruit were evaluated for ethylene production rate, respiration rate, and fruit quality at harvest and after 24 h at 20 C upon removal from cold storage after 3–6 months. Friction discoloration (FD) and senescence disorders were evaluated immediately upon removal from cold and after 7 d at 20 C, respectively, following 6 months of storage. 2.1.2. IEC, ethylene production rate and respiration rate IEC was measured in five fruit individually using a vacuumimmersion technique (Chen and Mellenthin, 1981). A 1 mL gas
2.1.4. FD and senescence disorders After removal from cold storage after 6 months, 30 fruit of each replicate were wetted by dipping in tap water at 20 C for 2 min. The wet fruit were passed through a 1.5 m elevator and a 6.0 m sorting belt in an experimental packing line with width of 300 mm. Fruit movement through the packing line was adjusted to be 400 g s 1. Fruit then were collected at the end of the sorting belt and placed into wooden boxes with polyethylene liners. FD was visually assessed after a simulated shipping time (2 weeks at 1.1 C) plus ripening (6 d at 20 C). Fruit with 3 disorder spots or 100 mm2 disorder area on the surface were considered as culls and incidence was expressed as FD percentage. Thirty fruit of each replicate were assessed for senescent scald (SS) and then cut longitudinally and transversely to assess senescent core breakdown (SCB). SS and SCB were expressed as percentage of incidence regardless of severity. 2.1.5. Ripening capacity FF was determined as described above on 10 fruit from each replicate after 7 (control and 1-MCP treated fruit) or 12 d (1-MCP treated fruit only) at 20 C following 3, 5, and 6 months of storage. 2.2. 1-MCP treatment delay study Twenty-four boxes (80 fruit per box) of ‘Bartlett’ pears were harvested at FF of 80.0 N (mid-commercial harvest maturity) from the orchard of MCAREC. Six boxes were treated with 1-MCP as described above and 6 boxes were untreated, then both 1-MCP treated and untreated control fruit were stored at 1.1 C. In addition, 6 boxes were held at 0 C and the other 6 boxes at 5 C for 12 d to simulate the time needed for filling a storage room. After
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Table 1 Maturity attributes of ‘Bartlett’ pears harvested at two physiological maturity stages (H1, H2) from two production elevations (E1, E2).
E1H1 E1H2 E2H1 E2H2
Elevation (m)
Harvest date
Flesh firmness (N)
150 150 610 610
10-Aug 15-Aug 27-Aug 10-Sep
84.5 76.1 83.2 75.6
1.3 0.9 1.8 1.3
Fruit peel chlorophyll content (IAD) 2.17 2.05 2.06 1.98
0.04 0.05 0.02 0.03
Internal ethylene concentration (mL L
1
)
0 0.08 0.05 0 0.35 0.13
Values are means SD.
the delay, the fruit were exposed to 1-MCP as described above, then stored at 1.1 C in air for 6 months. IEC and ethylene production rate were measured on the fruit immediately after harvest and upon removal from the delay at 0 and 5 C. Fruit quality (FF and color) and senescence disorders (SS and SCB) were evaluated upon removal from cold room and after ripening, respectively, following 6 months of storage.
2.3. Statistical analyses There were three replications per treatment at each evaluation period. The experimental design was completely randomized and the data were subjected to analysis of variance (ANOVA) using StatSoft1 Statistica version 6 (StatSoft, Tulsa, OK). When appropriate, means were separated by Fisher’s protected LSD test at p = 0.05.
Fig. 1. Ethylene production and respiration rate of 1-MCP treated ‘Bartlett’ pears on day 1 at 20 C affected by harvest maturity (H1 = harvest 1, H2 = harvest 2) and production elevation (E1 = 150 m, E2 = 610 m) following storage at 1.1 C for 6 months. Values are means SD.
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Fig. 2. Fruit flesh firmness (FF), fruit peel chlorophyll content (IAD), and titratable acidity (TA) of 1-MCP treated ‘Bartlett’ pears on day 1 at 20 C affected by harvest maturity (H1, H2) and production elevation (E1, E2) following storage at 1.1 C for 6 months. Values are means SD.
3. Results 3.1. Harvest maturity and production elevation study 3.1.1. Maturity parameters at harvest IEC was not detected in E1H1 and E2H1 at FF of 84.5 and 83.2 N, respectively (Table 1). In contrast, E1H2 (76.1 N) and E2H2 (75.6 N) accumulated IEC at 0.08 and 0.35 mL L 1, respectively. The chlorophyll content estimated by IAD reduced from H1 to H2 from both production elevations.
3.1.2. Ethylene production and respiration rate during cold storage The control fruit at both harvest maturity stages and from both production elevations increased ethylene production during 6 months of cold storage (Fig. 1). 1-MCP delayed and reduced ethylene production rate in all the fruit as expected but with different degrees of inhibition. The 1-MCP treated E1H1 and E2H1 fruit did not produce ethylene until 5 months and increased slightly thereafter, with ethylene production rate of 5.9 and 13.0 ng kg 1 s 1, respectively, at 6 months of storage (Fig. 1A and C). In contrast, the 1-MCP treated E1H2 and E2H2 fruit increased ethylene production at 3 months and produced ethylene of 19 and 48 ng kg 1 s 1, respectively, at 6 months of storage (Fig. 1B and D). Respiration rate increased in the control and 1-MCP inhibited it in all treatments during 6 months of storage (Fig. 1). While the 1-MCP treated E1H1 and E2H1 fruit maintained their respiration rate at initial levels at harvest during 6 months (Fig. 1E and F), the 1-MCP treated E1H2 and E2H2 fruit had increased respiration rate at 4 months and 3 months, respectively (Fig. 1G and H).
3.1.3. Fruit storage quality Fruit from all the treatments lost FF, IAD, and TA gradually during 6 months of storage (Fig. 2). In the control, regardless of production elevations, H1 fruit maintained FF > 66 N, IAD > 1.6, and TA > 41 meq L 1, but H2 fruit lost FF < 66 N, IAD < 1.4, and TA < 37 meq L 1 after 6 months of storage (Fig. 2). 1-MCP slowed down the loss rates of FF, IAD, and TA for E1H1, E2H1, and E1H2 fruit. However, E2H2 fruit did not respond to 1-MCP in terms of the losses of FF, IAD, and TA during 6 months. SSC did not change significantly (p = 0.05) in the control and 1-MCP treated fruit during 6 months of storage (data not shown). 3.1.4. Disorders Untreated E1H1, E1H2, E2H1, and E2H2 fruit developed SS of 35.1%, 61.7%, 23.9% and 58.6% and IB of 15.0%, 36.6%, 33.3% and 68.5%, respectively, after 6 months of storage (Fig. 3). 1-MCP prevented E1H1 and E2H1 fruit from developing SS and SCB. 1-MCP treated E1H2 and E2H2 fruit developed SS of 6.6% and 36.0% and SCB of 3.3% and 32.3%, respectively. H2 fruit were more susceptible to FD than H1 fruit from both elevations. 1-MCP reduced FD susceptibility for E1H1, E2H1, and E1H2, but not E2H2 fruit (Fig. 3E and F). 3.1.5. Ripening capacity While the control fruit of H1 and H2 from both elevations could ripen to FF < 23 N at 20 C within 7 d following 3, 5, and 6 months of cold storage, 1-MCP retarded ripening capacity as expected. Following 1-MCP treatment, at 3 months no fruit could ripen to FF < 23 N; at 5 months, all the fruit softened slightly but only E2H2 fruit reached FF < 23 N within 7 d at 20 C. 1-MCP treated
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Fig. 3. Senescent scald (SS), senescent core breakdown (SCB), and friction discoloration (FD) of 1-MCP treated ‘Bartlett’ pears on day 7 at 20 C affected by harvest maturity (H1, H2) and production elevation (E1, E2) following storage at 1.1 C for 6 months. Values are means SD. Different letters indicate significant differences between treatments (harvest maturity and production elevation) at each assessment according to Fisher’s protected LSD test at p = 0.05.
E1H1, E2H1, E2H1, and E2H2 fruit ripened to 33.8 N, 26.5 N, 25.3 N, and 17.6 N, respectively, within 7 d at 20 C following 6 months of cold storage (Fig. 4A and B). After 5 or 6 months of storage, it took 10–14 d for the 1-MCP treated E1H1, E2H1, and E2H1fruit to ripen to FF < 23 N at 20 C (Fig. 4C and D). 3.2. 1-MCP treatment delay study 3.2.1. Effect of holding temperature on ethylene synthesis Fruit harvested at FF = 80 N from an orchard at 150 m elevation produced neither a measurable amount of IEC nor a detectable ethylene production rate immediately after harvest and after 12 d at 0 C. In contrast, after 12 d at 5.0 C the fruit increased IEC to 0.59 mL L 1 and ethylene production rate to 2.5 ng kg 1 s 1 (Table 2). 3.2.2. Fruit storage quality and senescence disorders 1-MCP treatment immediately after harvest reduced the losses of FF and green color (Fig. 5A and B) and controlled SS and SCB significantly (Fig. 5C and D) compared to the non-treated control fruit after 6 months of cold storage. In comparison to the 1-MCP treatment immediately after harvest, a 12 d delay at 0 C between harvest and 1-MCP treatment did not affect 1-MCP efficacy in maintaining FF and green color and controlling SS and SCB. In contrast, the delayed 1-MCP treatment for 12 d at 5 C lost its efficacy in maintaining FF and color and controlling SS, and SCB (p = 0.05) compared to the non-treated control. Holding fruit at 5 C for 12 d prior to storing at 1.1 C reduced FF and IAD by 10.5 and 9.2% and increased SS and SCB incidences by 62.5 and 233.3%, respectively, evaluated after 6 months compared to storing the fruit at 1.1 C immediately after harvest (Fig. 5).
4. Discussion SS and SCB are major senescence disorders that limit storage life of ‘Bartlett’ pear (Villalobos-Acuña et al., 2011a; Wang and Sugar, 2013). Wholesale buyers prefer ‘Bartlett’ pears firm to resist mechanical damage with dark green skin color upon entry into the shipment and distribution chain. For field bin storage, FD is a significant concern in the pear industry. According to Thompson (2007), ‘Bartlett’ fruit ripened with FF < 66 N would likely suffer vibration and/or impact bruising damage during packing or transportation. This study shows that 1-MCP controls the senescence disorders, retards FF and green color losses, and reduces FD of ‘Bartlett’ pear after long-term storage through inhibiting ethylene production as previously observed (Calvo and Sozzi, 2009; DeEll and Ehsani-Moghaddam, 2011; Ekman et al., 2004; Feng et al., 2004; Trinchero et al., 2004; Villalobos-Acuña et al., 2011a,b). These results, however, indicate that the response of the PNW ‘Bartlett’ pear to 1-MCP is affected by fruit maturity, production elevation, and the holding temperature between harvest and 1-MCP treatment during storage room filling, which may result in its inconsistent efficacy in commercial application. FF is currently the commercial indicator of harvest timing for European pears in the PNW. Harvest starts when FF reaches 83.6 N and completes at 74.8 N, within 10–14 d in the growing region for ‘Bartlett’ (Chen, 2004; Wang et al., 2015). We found that 1-MCP had its highest efficacy on controlling the disorders of fruit harvested at the early commercial harvest maturity and least efficacy on fruit harvested at late maturity. Accordingly, IEC was not detected in the early harvested fruit, but accumulated in the late harvested fruit. It is reported that 1-MCP efficacy on ripening/senescence inhibition of climacteric fruit is affected by harvest maturity, with a reduced efficacy on more mature fruit (Chiriboga et al., 2013; Gamrasni
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Fig. 4. Fruit ripening capacity expressed as flesh firmness (FF) of 1-MCP treated ‘Bartlett’ pears on day 7 (A and B) and 12 at 20 C affected by harvest maturity (H1, H2) and production elevation (E1, E2) following storage at 1.1 C for 3, 5, and 6 months. Values are means SD.
et al., 2010; Jung and Watkins, 2014; Macnish et al., 2012; Mir et al., 2001; Villalobos-Acuña et al., 2011a,b; Watkins, 2008). The increase of IEC in more mature fruit at the time of treatment reduces a delay of tomato or avocado ripening by 1-MCP (Zhang et al., 2009, 2010, 2011). The increased ethylene production or IEC possibly reduce the competitive ability of 1-MCP molecules to bind to available receptors in climacteric fruit (Sisler and Serek, 1997). In the PNW, ‘Bartlett’ pear is produced at a range of elevations (from 100 m to 600 m in the Mid-Columbia area). We found that fruit harvested from different elevations (150 m and 610 m) with the same FF at a late harvest maturity (74.8 N) accumulated different levels of IEC. Fruit from the higher elevation accumulated higher IEC and lost its response to 1-MCP with respect to maintaining FF and green color and controlling storage disorders. The location where ‘Bartlett’ pears are grown has been shown to be an important factor affecting ethylene production and storage disorders (Agar et al., 1999; Whitaker et al., 2009). Ethylene production increased in ‘Bartlett’ pears that experienced cooler preharvest temperatures (Agar et al., 1999; Wang et al., 1971). Therefore, the fruit produced in higher elevations with cooler preharvest temperatures should be harvested in earlier maturity stages to avoid losing 1-MCP efficacy. The soil may also affect the fruit physiology and especially the ability of the fruit to regulate ethylene production. This could be another factor which can result in differences in response to 1-MCP treatment for fruit grown in different orchards. This may also suggest that FF may not be an accurate indicator of physiological status related to fruit maturity as suggested by Sugar and Basile (2013) and Villalobos-Acuña et al. (2011a), and that other factors including weather and tree management may influence fruit response to 1-MCP treatment. It typically takes 7–12 d to fill a pear storage room in the PNW until 1-MCP treatment can be carried out. The holding temperature during a 12 d delay between harvest and 1-MCP treatment affected
IEC accumulation, and therefore, 1-MCP efficacy on extending storage life of ‘Bartlett’ pear. A holding temperature at 5.0 C for 12 d increased IEC accumulation to a level that reduced 1-MCP efficacy on inhibiting senescence and controlling storage disorders of the PNW ‘Bartlett’ pear. Furthermore, ethylene production rate was increased in the fruit stored at 5 C for 12 d. Villalobos-Acuña et al. (2011a) reported that exogenous ethylene as little as 0.3 mL L 1 in the 1-MCP treating environment significantly reduced 1-MCP efficacy in ripening inhibition of ‘Bartlett’ pear. Therefore, a fast pre-cooling immediately after harvest and holding fruit at low temperature (i.e., 0 C) before 1-MCP treatment are necessary to prevent or reduce IEC accumulation and maximize 1-MCP efficacy on ‘Bartlett’ pear. European pears are resistant to ripening after harvest, however, they are enjoyed by consumers when fruit have ripened to a buttery and juicy texture at warm temperatures in 5–7 d depending on cultivar (Chen, 2004; Villalobos-Acuña and Mitcham, 2008). A period of cold storage or ethylene conditioning induces European pears ethylene synthesis and development of ripening capacity (Villalobos-Acuña and Mitcham, 2008; Makkumrai et al., 2014). 1-MCP treatment inhibits ‘Bartlett’ pear ethylene synthesis and controls storage disorders, which, unfortunately, reduces the ripening capacity as previously reported in European pears (Argenta et al., 2003; Bai et al., 2006; Chen and Spotts, 2005; Chiriboga et al., 2013; Villalobos-Acuña et al., 2011a; Xie et al., 2014). The optimum firmness for an ideal eating quality of European pears with buttery and juicy texture ranges between 14 and 23 N (Chen et al., 2003; Kappel et al., 1995). In this study, all the 1-MCP treated ‘Bartlett’ pears did not develop ripening capacity before 3 months of cold storage. The 1-MCP treated E1H1, E1H2, and E2H1 fruit developed certain degree of ripening capacity after 5 or 6 months of storage, but took 10–14 d to ripen to FF < 23 N.
Table 2 Effect of holding temperature during a 12 d delay between harvest and 1-MCP treatment on internal ethylene concentration and ethylene production rate of ‘Bartlett’ pears harvested at FF = 80.0 N from E1. Holding condition
Internal ethylene concentration (mL L
At harvest 12 d at 0 C 12 d at 5 C
0 0 0.59 0.38
Values are means SD.
1
)
Ethylene production rate (ng kg 0 0 2.5 1.1
1
s
1
)
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Fig. 5. Fruit flesh firmness (FF), peel chlorophyll content, senescent scald (SS), and senescent core breakdown (SCB) of 1-MCP treated ‘Bartlett’ pears affected by holding temperature during a 12 d delay between harvest and 1-MCP treatment after storage at 1.1 C for 6 months. Values are means SD. Different letters indicate significant differences between treatments at each assessment according to Fisher’s protected LSD test at p = 0.05.
5. Conclusion 1-MCP can extend the packing season and prevent storage disorders of ‘Bartlett’ pear. To ensure a consistent efficacy in commercial application, any factors affecting ethylene production or the physiological maturity stage at the time of 1-MCP treatment should be taken into consideration. These factors have been identified as harvest maturity, production elevation, and holding temperature between harvest and 1-MCP treatment. However, a continuing challenge for commercializing 1-MCP on European pears is how to ripen the 1-MCP treated fruit to their ideal eating quality in about 7 d at room temperature following cold storage. More research is warranted to investigate conditioning technologies such as moderate warm temperatures and ethylene conditioning to adequately ripen 1-MCP treated European pears. Acknowledgements We are grateful to the Columbia Gorge Fruit Growers Association, the PNW Pear Research Committees, and the Oregon State Agricultural Experiment Station for financial support. References Agar, I.T., Biasi, W.V., Mitcham, E.J., 1999. Exogenous ethylene accelerates ripening responses in Bartlett pears regardless of maturity or growing region. Postharvest Biol. Technol. 12, 67–78. Argenta, L.C., Fan, X.T., Mattheis, J.P., 2003. Influence of 1-methylcyclopropene on ripening storage life, and volatile production by ‘d’Anjou' cv. pear fruit. J. Agric. Food Chem. 51, 3858–3864. Bai, J., Mattheis, J.P., Reed, N., 2006. Re-initiating softening ability of 1methylcyclopropene-treated ‘Anrtlett’ and ‘d’Anjou' pears after regular air or controlled atmosphere storage. J. Hortic. Sci. Biotechnol. 81, 959–964. Calvo, G., Sozzi, G.O., 2009. Effectiveness of 1-MCP treatment on ‘Bartlett’ pears as influenced by the cooling method and the bin material. Postharvest Biol. Technol. 51, 49–55.
Chen, P.M., 2004. Pear. In: Gross, K.C., Wang, C.Y., Saltveit, M. (Eds.), The Commercial 556 Storage of Fruits, Vegetables, and Florist and Nursery Crops. USDA, ARS, Agriculture 557 Handbook 66. http://www.ba.ars.usda.gov/hb66/107pear.pdf. Chen, P.M., Mellenthin, W.M., 1981. Effects of harvest date on ripening capacity and postharvest life of ‘d’Anjou’ pears. J. Amer. Soc. Hort. Sci. 106, 38–42. Chen, P.M., Spotts, R.A., 2005. Changes in ripening behaviors of 1-MCP-treated ‘d’Anjou' pears after storage. Int. J. Fruit Sci. 5, 3–17. Chen, P.M., Varga, D.M., Seavert, C.F., 2003. Developing a value-added fresh-cut ‘d’Anjou' pear product. HortTechnology 13, 314–320. Chiriboga, M.-A., Schotsmans, W.C., Larrigaudière, C., Dupille, E., Recasens, I., 2013. Responsiveness of ‘Conference’ pears to 1-methylcyclopropene: the role of harvest date, orchard location and year. J. Sci. Food Agric. 93, 619–625. DeEll, J.R., Ehsani-Moghaddam, B., 2011. Timing of postharvest 1methylcyclopropene treatment affects Bartlett pear quality after storage. Can. J. Plant Sci. 91, 853–858. DeEll, J.R., Murr, D.P., Porteous, M.D., Rupasinghe, H.P.V., 2002. Influence of temperature and duration of 1-methylcyclopropene (1-MCP) treatment on apple quality. Postharvest Biol. Technol. 24, 349–353. Ekman, J.H., Clayton, M., Biasi, W.V., Mitcham, E.J., 2004. Interaction between 1-MCP concentration: treatment interval and storage time for ‘Bartlett’ pears. Postharvest Biol. Technol. 31, 127–136. Feng, X., Biasi, B., Mitcham, E.J., 2004. Effects of various coatings and antioxidants on peel browning of ‘Bartlett’ pears. J. Sci. Food Agric. 84, 595–600. Gamrasni, D., Ben-Arie, R., Goldway, M., 2010. 1-Methylcyclopropene (1-MCP) application to Spadona pears at different stages of ripening to maximize fruit quality after storage. Postharvest Biol. Technol. 58, 104–112. Ju, Z., Curry, E.A., Duan, Y., Ju, Z., Guo, A., 2001. Plant oil emulsions prevent senescent scald and core breakdown and reduce fungal decay in ‘Bartlett’ pears. J. Am. Soc. Hortic. Sci. 126, 358–363. Jung, S.K., Watkins, C.B., 2014. Internal ethylene concentrations in apple fruit at harvest affect persistence of inhibition of ethylene production after1methylcyclopropene treatment. Postharvest Biol. Technol. 50, 45–52. Kappel, F., Fisher-Fleming, R., Hogue, E.J., 1995. Ideal pear sensory attributes and fruit characteristic. HortScience 30, 988–993. Makkumrai, W., Anthon, G.E., Sivertsen, H., Ebeler, S.E., Negre-Zakharov, F., Barrett, D.M., Mitcham, E.J., 2014. Effect of ethylene and temperature conditioning on sensory attributes and chemical composition of ‘Bartlett’ pears. Postharvest Biol. Technol. 97, 44–61. Macnish, A.J., Mitcham, E.J., Holcroft, D.M., 2012. Endogenous and exogenous ethylene modulates the response of ‘Bartlett’ pears to 1-methylcyclopropene. Acta Hortic. 945, 309–316. Mir, N.A., Curell, E., Khan, N., Whitaker, M., Beaudry, R.M., 2001. Harvest maturity, storage temperature, and 1-MCP application frequency alter firmness retention
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and chlorophyll fluorescence of ‘Redchief Delicious’ apples. J. Am. Soc. Hortic. Sci. 126, 618–624. Sisler, E.C., Serek, M., 1997. Inhibitors of ethylene responses in plants at the receptor level: recent developments. Physiol. Plant. 100, 577–582. Sugar, D., Basile, S.R., 2013. Integrated ethylene and temperature conditioning for induction of ripening capacity in ‘Anjou’ and ‘Comice’ pears. Postharvest Biol. Technol. 83, 9–16. Thompson, J.F., 2007. Reducing fruit injury during postharvest handling and transportation. In: Mitcham, E.J., Elkins, R.B. (Eds.), Pear Production and Handling Manual. University of California, pp. 167–170 Div. Agric. Nat. Res., Pub. 3483. Trinchero, G.D., Sozzi, G.O., Covatta, F., Fraschina, A.A., 2004. Inhibition of ethylene action by 1-methylcyclopropene extends postharvest life of ‘Bartlett’ pears. Postharvest Biol. Technol. 32, 193–204. Villalobos-Acuña, M.G., Biasi, W.V., Flores, S., Jiang, C.Z., Reid, M.S., Willits, N.H., Mitcham, E.J., 2011a. Effect of maturity and cold storage on ethylene biosynthesis and ripening in ‘Bartlett’ pears treated after harvest with 1-MCP. Postharvest Biol. Technol. 59, 1–9. Villalobos-Acuña, M.G., Biasi, W.V., Mitcham, E.J., Holcroft, D., 2011b. Fruit temperature and ethylene modulate 1-MCP response in ‘Bartlett’ pears. Postharvest Biol. Technol. 60, 17–23. Villalobos-Acuña, M.G., Mitcham, E.J., 2008. Ripening of European pears: the chilling dilemma. Postharvest Biol. Technol. 60, 17–23. Wang, C.Y., Mellenthin, W.M., Hansen, E., 1971. Effect of temperature on development of premature ripening in Bartlett pears. J. Am. Soc. Hortic. Sci. 96, 122–125. Wang, Y., Sugar, D., 2013. Internal browning disorder and fruit quality in modified atmosphere packaged ‘Bartlett’ pears during storage and transit. Postharvest Biol. Technol. 83, 72–82. Wang, Y., Castagnoli, S., Sugar, D., 2015. Integrating IAD index into the current firmness-based maturity assessment of European pears. Acta Hortic. (in press).
Watkins, C.B., 2006. The use of 1-methylcyclopropene (1-MCP) on fruits and vegetables. Biotechnol. Adv. 24, 389–409. Watkins, C.B., 2008. Overview of 1-methylcyclopropene trials and uses for edible horticultural crops. HortScience 43, 86–94. Watkins, C.B., Nock, J.F., 2005. Effects of delays between harvest and 1methylcyclopropene treatment, and temperature during treatment, on ripening of air-stored and controlled-atmosphere-stored apples. HortScience 40, 2096–2101. Whitaker, B.D., Villalobos-Acuña, M.G., Mitcham, E.J., Mattheis, J.P., 2009. Superficial scald susceptibility and a-farnesene metabolism in ‘Bartlett’ pears grown in California and Washington. Postharvest Biol. Technol. 53, 43–50. Xie, X., Song, J., Wang, Y., Sugar, D., 2014. Ethylene synthesis and ripening capacity of 1-MCP treated ‘d’Anjou’ pears affected by storage temperatures. Postharvest Biol. Technol. 97, 1–10. Zhang, Z., Huber, D.J., Hurr, B.M., Rao, J., 2009. Delay of tomato fruit ripening in response to 1-methylcyclopropene is influenced by internal ethylene levels. Postharvest Biol. Technol. 54, 1–8. Zhang, Z.K., Huber, D.J., Rao, J.P., 2010. Short-term hypoxic hypobaria transiently decreases internal ethylene levels and increases sensitivity of tomato fruit to subsequent 1-methylcyclopropene treatments. Postharvest Biol. Technol. 56, 131–137. Zhang, Z., Huber, D.J., Rao, J., 2011. Ripening delay of mid-climacteric avocado fruit in response to elevated doses of 1-methylcyclopropene and hypoxia-mediated reduction in internal ethylene concentration. Postharvest Biol. Technol. 60, 83–91. Ziosi, V., Noferini, M., Fiori, G., Tadiello, A., Trainotti, L., Casadoro, G., Costa, G., 2008. A new index based on vis spectroscopy to characterize the progression of ripening in peach fruit. Postharvest Biol. Technol. 49, 319–329.
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Postharvest Biology and Technology journal homepage: www.elsevier.com/locate/postharvbio
1-MCP efficacy in extending storage life of ‘Bartlett’ pears is affected by harvest maturity, production elevation, and holding temperature during treatment delay Yan Wang a, * , David Sugar b a Department of Horticulture, Oregon State University, Mid-Columbia Agricultural Research and Extension Center, 3005 Experiment Station Dr., Hood River, OR 97031, USA b Oregon State University, Southern Oregon Research and Extension Center, 569 Hanley Rd., Medford, OR 97502,USA
A R T I C L E I N F O
A B S T R A C T
Article history: Received 26 October 2014 Received in revised form 24 February 2015 Accepted 25 February 2015
The efficacy of 1-methylcyclopropene (1-MCP) in extending storage life of the Pacific Northwest ‘Bartlett’ pear is inconsistent. The effects of harvest maturity [H1: flesh firmness (FF) 83.6 N; H2: FF 74.8 N], production elevation (E1 150 m; E2 610 m), and holding temperature (0 and 5 C) prior to application of 1-MCP have been measured with respect to ethylene production, fruit quality, and storage disorders of ‘Bartlett’ fruit during 6 months of storage at 1.1 C. 1-MCP at 0.3 mL L 1 for 24 h at 0 C inhibited ethylene production, FF and green color losses, senescence disorders, and friction discoloration for H1 fruit from both elevations. However, 1-MCP efficacy was reduced moderately in E1H2 fruit and reduced to a greater extend in E2H2 fruit. Internal ethylene concentration (IEC) at harvest was not detected in H1 fruit from either elevation, but it accumulated in E1H2 and E2H2 fruit (E2H2 > E1H2). The holding temperature at 5 C but not 0 C for 12 d between harvest and 1-MCP treatment increased fruit IEC and ethylene production rate and reduced the fruit response to subsequent 1-MCP treatment. The fruit physiological stage at the moment of 1-MCP treatment determined the efficacy of 1-MCP in extending the storage life of ‘Bartlett’ pears. 1-MCP retarded development of ripening capacity and 10–14 d at 20 C were needed to ripen 1-MCP treated ‘Bartlett’ pears to optimum eating quality following 5–6 months of cold storage. ã 2015 Elsevier B.V. All rights reserved.
Keywords: Pyrus communis 1-MCP Harvest maturity Production elevation Delayed application Storage disorders Ripening capacity
1. Introduction In the U.S. Pacific Northwest (PNW), ‘Bartlett’ pears are normally stored for 1–3 months in regular air (RA) or 3–5 months in controlled atmosphere (CA) storage at 1.1 C (Wang and Sugar, 2013). ‘Bartlett’ pear storage life is often shortened and significant losses may occur after long-term storage or long-distant shipping due to senescence disorders such as yellowing, senescent scald (SS) and senescent core breakdown (SCB) (Ju et al., 2001; VillalobosAcuña et al., 2011a). A portion of ‘Bartlett’ pear production in the PNW is stored in field bins, and friction discoloration (FD) can occur during packing after storage. In recent years, a trend of moving from cannery to fresh market has increased the need to extend ‘Bartlett’ storage life to prolong the packing and marketing seasons. Development of the storage disorders and a relatively short storage life of ‘Bartlett’ pear are associated with increased ethylene
* Corresponding author. Tel.: +1 541 386 2030; fax: +1 541 386 1905. E-mail address: [email protected] (Y. Wang). http://dx.doi.org/10.1016/j.postharvbio.2015.02.013 0925-5214/ ã 2015 Elsevier B.V. All rights reserved.
production induced by cold storage (Ekman et al., 2004; VillalobosAcuña et al., 2011a). 1-Methylcyclopropene (1-MCP) is an ethylene action inhibitor that delays senescence and ripening of many fruit, including European pears, through irreversible binding to ethylene receptors of fruit cells (Sisler and Serek, 1997; Watkins, 2006). 1-MCP inhibits ethylene production and eliminates or reduces SS and SCB of ‘Bartlett’ pear after cold storage (Bai et al., 2006; Calvo and Sozzi, 2009; DeEll and Ehsani-Moghaddam, 2011; Ekman et al., 2004; Trinchero et al., 2004; Villalobos-Acuña et al., 2011a,b). European pears (Pyrus communis) are enjoyed by consumers when fruit have ripened to a buttery and juicy texture at warm temperatures following cold storage (Chen, 2004; Xie et al., 2014). The response of European pears to 1-MCP is affected by application conditions such as 1-MCP concentration, exposure duration, exposure temperature, and presence of exogenous ethylene in the treating room (Argenta et al., 2003; Chen and Spotts, 2005; DeEll et al., 2002; Ekman et al., 2004; Villalobos-Acuña et al., 2011b). 1-MCP at higher rates can eliminate the ripening capacity of European pears (Chen and Spotts, 2005; Bai et al., 2006). To balance between reducing senescence disorders and the recovery of ripening capacity after cold storage, recommended 1-MCP
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treatment for ‘Bartlett’ pears is 0.3 mL L 1 for 24 h. Recent studies in our laboratory indicate that if temperatures of 10–20 C occur during a 24 h 1-MCP treatment yellowing of ‘Bartlett’ pears is accelerated during subsequent storage at 1.1 C. While the pear industry is highly interested in commercializing 1-MCP to extend the packing season and reduce storage and shipping losses of ‘Bartlett’, its efficacy is found to be quite variable during commercial application in the PNW (industry communication). It was also reported that in many cases no response was seen or that a much higher concentration of 1-MCP was required to have an effect on ‘Bartlett’ in commercial applications in California (Villalobos-Acuña et al., 2011b). It is known that factors such as fruit maturity at the time of treatment, application delay after harvest, and production lot affect 1-MCP efficacy on different fruit (Mir et al., 2001; Villalobos-Acuña et al., 2011a,b; Watkins and Nock, 2005; Zhang et al., 2009). In the PNW, ‘Bartlett’ pears are harvested when flesh firmness (FF) declines to between 83.6 and 74.8 N (Chen, 2004). A storage room is often filled with ‘Bartlett’ fruit from a range of production elevations and it may take 12 d to fill a storage room before it is ready for 1-MCP treatment. The commercial harvest maturity, production elevation, and holding temperature during the period of room filling may affect fruit ethylene synthesis, therefore the response degree of fruit to 1-MCP. The objective of this study was to determine the effects of early/late commercial harvest maturity (83.6/74.8 N), lower/higher production elevation (150/600 m) in the mid-Columbia area, and holding temperature (0 and 5 C) during a 12 d delay between harvest and 1-MCP treatment on 1-MCP efficacy with respect to ethylene production, storage disorders, and ripening capacity of ‘Bartlett’ pears during subsequent 6 months of storage at 1.1 C. 2. Materials and methods
sample was injected into a gas chromatograph (Shimadzu GC-8A, Kyoto, Japan). Nitrogen was used as the carrier gas at a flow rate of 0.8 mL s 1. The injector and detector port temperatures were 90 and 140 C, respectively. An external standard of ethylene (1.0 mL L 1) was used for calibration. The limit of ethylene detection was approximately 0.08 mL L 1. Ethylene production and CO2 production rates were measured by incubating five fruit per replicate in a 3.8 L airtight jar for 1 h at 20 C. Gas samples were withdrawn through a septum on the top using a 1 mL gas-tight syringe. Ethylene was measured with the same GC system used for IEC determination. Ethylene production rate was expressed as ng kg 1 s 1. The headspace CO2 concentration was measured using an O2 and CO2 analyzer (Model 900161, Bridge Analyzers Inc., Alameda, CA, USA). Fruit respiration rate was expressed as mg CO2 kg 1 s 1. 2.1.3. Fruit storage quality Fruit quality was measured on 10 fruit of each replicate. Peel chlorophyll content was estimated using a DA meter (Sinteleia, Bolonga, Italy) and expressed as IAD value (Ziosi et al., 2008). Measurements were taken on opposite sides of the equator of each fruit. After color determination, FF was measured using a fruit texture analyzer (model GS-14, Guss Manufacturing Ltd., Strand, South Africa) with an 8 mm probe that penetrates 9 mm in 0.9 s. Two measurements were obtained per fruit on opposite sides of the equator after removal of 20 mm diameter peel discs. After chlorophyll and FF determination, flesh tissue of 0.1 kg was ground for 3 min in a juice extractor (Acme Model 6001) equipped with a uniform strip of milk filter. Titratable acidity (TA) was determined by titrating 10 mL of the juice to pH 8.1 using 0.1 N NaOH with a commercial titration system (Model T80/20, Schott-Gerate, Hofheim, Germany) and expressed as meq L 1 of juice. Soluble solid content (SSC) was determined using a hand held refractometer (Atago, Tokyo, Japan) and expressed as a percentage.
2.1. Harvest maturity and production elevation study 2.1.1. Fruit materials and 1-MCP treatment ‘Bartlett’ pears were harvested at FF of 84.5 (H1) and 76.1 N (H2) from the orchard at Oregon State University’s Mid-Columbia Agricultural Research and Extension Center (MCAREC) in Hood River, OR, USA (45.7 N, 121.5 W, elevation 150 m) and labeled as E1. ‘Bartlett’ fruit were also harvested at FF of 83.2 (H1) and 75.6 N (H2) from an orchard in Parkdale, OR, USA (45.5 N, 121.6 W, elevation 610 m) and labeled as E2. Defect-free fruit were randomly packed in 48 wooden boxes (80 fruit per box) with standard perforated polyethylene liners and were cooled overnight at 0 C. On the second day, half of the fruit in each group (E1H1, E1H2, E2H1, E2H2) were exposed to 0.3 mL L 1. 1-MCP released from SmartFresh1 tabs provided by AgroFresh (Springhouse, PA, USA) in an airtight room (39.75 m3) with a circulation fan at 0 C for 24 h. Fruit of the other half were held at 0 C as untreated control. Following 1-MCP treatment, fruit with or without 1-MCP treatment were then stored at 1.1 C in air for 6 months. Fruit maturity attributes: FF, fruit color, and internal ethylene concentration (IEC) were determined immediately after harvest on E1H1, E1H2, E2H1, and E2H2 fruit. The control and 1-MCP treated fruit were evaluated for ethylene production rate, respiration rate, and fruit quality at harvest and after 24 h at 20 C upon removal from cold storage after 3–6 months. Friction discoloration (FD) and senescence disorders were evaluated immediately upon removal from cold and after 7 d at 20 C, respectively, following 6 months of storage. 2.1.2. IEC, ethylene production rate and respiration rate IEC was measured in five fruit individually using a vacuumimmersion technique (Chen and Mellenthin, 1981). A 1 mL gas
2.1.4. FD and senescence disorders After removal from cold storage after 6 months, 30 fruit of each replicate were wetted by dipping in tap water at 20 C for 2 min. The wet fruit were passed through a 1.5 m elevator and a 6.0 m sorting belt in an experimental packing line with width of 300 mm. Fruit movement through the packing line was adjusted to be 400 g s 1. Fruit then were collected at the end of the sorting belt and placed into wooden boxes with polyethylene liners. FD was visually assessed after a simulated shipping time (2 weeks at 1.1 C) plus ripening (6 d at 20 C). Fruit with 3 disorder spots or 100 mm2 disorder area on the surface were considered as culls and incidence was expressed as FD percentage. Thirty fruit of each replicate were assessed for senescent scald (SS) and then cut longitudinally and transversely to assess senescent core breakdown (SCB). SS and SCB were expressed as percentage of incidence regardless of severity. 2.1.5. Ripening capacity FF was determined as described above on 10 fruit from each replicate after 7 (control and 1-MCP treated fruit) or 12 d (1-MCP treated fruit only) at 20 C following 3, 5, and 6 months of storage. 2.2. 1-MCP treatment delay study Twenty-four boxes (80 fruit per box) of ‘Bartlett’ pears were harvested at FF of 80.0 N (mid-commercial harvest maturity) from the orchard of MCAREC. Six boxes were treated with 1-MCP as described above and 6 boxes were untreated, then both 1-MCP treated and untreated control fruit were stored at 1.1 C. In addition, 6 boxes were held at 0 C and the other 6 boxes at 5 C for 12 d to simulate the time needed for filling a storage room. After
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Table 1 Maturity attributes of ‘Bartlett’ pears harvested at two physiological maturity stages (H1, H2) from two production elevations (E1, E2).
E1H1 E1H2 E2H1 E2H2
Elevation (m)
Harvest date
Flesh firmness (N)
150 150 610 610
10-Aug 15-Aug 27-Aug 10-Sep
84.5 76.1 83.2 75.6
1.3 0.9 1.8 1.3
Fruit peel chlorophyll content (IAD) 2.17 2.05 2.06 1.98
0.04 0.05 0.02 0.03
Internal ethylene concentration (mL L
1
)
0 0.08 0.05 0 0.35 0.13
Values are means SD.
the delay, the fruit were exposed to 1-MCP as described above, then stored at 1.1 C in air for 6 months. IEC and ethylene production rate were measured on the fruit immediately after harvest and upon removal from the delay at 0 and 5 C. Fruit quality (FF and color) and senescence disorders (SS and SCB) were evaluated upon removal from cold room and after ripening, respectively, following 6 months of storage.
2.3. Statistical analyses There were three replications per treatment at each evaluation period. The experimental design was completely randomized and the data were subjected to analysis of variance (ANOVA) using StatSoft1 Statistica version 6 (StatSoft, Tulsa, OK). When appropriate, means were separated by Fisher’s protected LSD test at p = 0.05.
Fig. 1. Ethylene production and respiration rate of 1-MCP treated ‘Bartlett’ pears on day 1 at 20 C affected by harvest maturity (H1 = harvest 1, H2 = harvest 2) and production elevation (E1 = 150 m, E2 = 610 m) following storage at 1.1 C for 6 months. Values are means SD.
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Fig. 2. Fruit flesh firmness (FF), fruit peel chlorophyll content (IAD), and titratable acidity (TA) of 1-MCP treated ‘Bartlett’ pears on day 1 at 20 C affected by harvest maturity (H1, H2) and production elevation (E1, E2) following storage at 1.1 C for 6 months. Values are means SD.
3. Results 3.1. Harvest maturity and production elevation study 3.1.1. Maturity parameters at harvest IEC was not detected in E1H1 and E2H1 at FF of 84.5 and 83.2 N, respectively (Table 1). In contrast, E1H2 (76.1 N) and E2H2 (75.6 N) accumulated IEC at 0.08 and 0.35 mL L 1, respectively. The chlorophyll content estimated by IAD reduced from H1 to H2 from both production elevations.
3.1.2. Ethylene production and respiration rate during cold storage The control fruit at both harvest maturity stages and from both production elevations increased ethylene production during 6 months of cold storage (Fig. 1). 1-MCP delayed and reduced ethylene production rate in all the fruit as expected but with different degrees of inhibition. The 1-MCP treated E1H1 and E2H1 fruit did not produce ethylene until 5 months and increased slightly thereafter, with ethylene production rate of 5.9 and 13.0 ng kg 1 s 1, respectively, at 6 months of storage (Fig. 1A and C). In contrast, the 1-MCP treated E1H2 and E2H2 fruit increased ethylene production at 3 months and produced ethylene of 19 and 48 ng kg 1 s 1, respectively, at 6 months of storage (Fig. 1B and D). Respiration rate increased in the control and 1-MCP inhibited it in all treatments during 6 months of storage (Fig. 1). While the 1-MCP treated E1H1 and E2H1 fruit maintained their respiration rate at initial levels at harvest during 6 months (Fig. 1E and F), the 1-MCP treated E1H2 and E2H2 fruit had increased respiration rate at 4 months and 3 months, respectively (Fig. 1G and H).
3.1.3. Fruit storage quality Fruit from all the treatments lost FF, IAD, and TA gradually during 6 months of storage (Fig. 2). In the control, regardless of production elevations, H1 fruit maintained FF > 66 N, IAD > 1.6, and TA > 41 meq L 1, but H2 fruit lost FF < 66 N, IAD < 1.4, and TA < 37 meq L 1 after 6 months of storage (Fig. 2). 1-MCP slowed down the loss rates of FF, IAD, and TA for E1H1, E2H1, and E1H2 fruit. However, E2H2 fruit did not respond to 1-MCP in terms of the losses of FF, IAD, and TA during 6 months. SSC did not change significantly (p = 0.05) in the control and 1-MCP treated fruit during 6 months of storage (data not shown). 3.1.4. Disorders Untreated E1H1, E1H2, E2H1, and E2H2 fruit developed SS of 35.1%, 61.7%, 23.9% and 58.6% and IB of 15.0%, 36.6%, 33.3% and 68.5%, respectively, after 6 months of storage (Fig. 3). 1-MCP prevented E1H1 and E2H1 fruit from developing SS and SCB. 1-MCP treated E1H2 and E2H2 fruit developed SS of 6.6% and 36.0% and SCB of 3.3% and 32.3%, respectively. H2 fruit were more susceptible to FD than H1 fruit from both elevations. 1-MCP reduced FD susceptibility for E1H1, E2H1, and E1H2, but not E2H2 fruit (Fig. 3E and F). 3.1.5. Ripening capacity While the control fruit of H1 and H2 from both elevations could ripen to FF < 23 N at 20 C within 7 d following 3, 5, and 6 months of cold storage, 1-MCP retarded ripening capacity as expected. Following 1-MCP treatment, at 3 months no fruit could ripen to FF < 23 N; at 5 months, all the fruit softened slightly but only E2H2 fruit reached FF < 23 N within 7 d at 20 C. 1-MCP treated
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Fig. 3. Senescent scald (SS), senescent core breakdown (SCB), and friction discoloration (FD) of 1-MCP treated ‘Bartlett’ pears on day 7 at 20 C affected by harvest maturity (H1, H2) and production elevation (E1, E2) following storage at 1.1 C for 6 months. Values are means SD. Different letters indicate significant differences between treatments (harvest maturity and production elevation) at each assessment according to Fisher’s protected LSD test at p = 0.05.
E1H1, E2H1, E2H1, and E2H2 fruit ripened to 33.8 N, 26.5 N, 25.3 N, and 17.6 N, respectively, within 7 d at 20 C following 6 months of cold storage (Fig. 4A and B). After 5 or 6 months of storage, it took 10–14 d for the 1-MCP treated E1H1, E2H1, and E2H1fruit to ripen to FF < 23 N at 20 C (Fig. 4C and D). 3.2. 1-MCP treatment delay study 3.2.1. Effect of holding temperature on ethylene synthesis Fruit harvested at FF = 80 N from an orchard at 150 m elevation produced neither a measurable amount of IEC nor a detectable ethylene production rate immediately after harvest and after 12 d at 0 C. In contrast, after 12 d at 5.0 C the fruit increased IEC to 0.59 mL L 1 and ethylene production rate to 2.5 ng kg 1 s 1 (Table 2). 3.2.2. Fruit storage quality and senescence disorders 1-MCP treatment immediately after harvest reduced the losses of FF and green color (Fig. 5A and B) and controlled SS and SCB significantly (Fig. 5C and D) compared to the non-treated control fruit after 6 months of cold storage. In comparison to the 1-MCP treatment immediately after harvest, a 12 d delay at 0 C between harvest and 1-MCP treatment did not affect 1-MCP efficacy in maintaining FF and green color and controlling SS and SCB. In contrast, the delayed 1-MCP treatment for 12 d at 5 C lost its efficacy in maintaining FF and color and controlling SS, and SCB (p = 0.05) compared to the non-treated control. Holding fruit at 5 C for 12 d prior to storing at 1.1 C reduced FF and IAD by 10.5 and 9.2% and increased SS and SCB incidences by 62.5 and 233.3%, respectively, evaluated after 6 months compared to storing the fruit at 1.1 C immediately after harvest (Fig. 5).
4. Discussion SS and SCB are major senescence disorders that limit storage life of ‘Bartlett’ pear (Villalobos-Acuña et al., 2011a; Wang and Sugar, 2013). Wholesale buyers prefer ‘Bartlett’ pears firm to resist mechanical damage with dark green skin color upon entry into the shipment and distribution chain. For field bin storage, FD is a significant concern in the pear industry. According to Thompson (2007), ‘Bartlett’ fruit ripened with FF < 66 N would likely suffer vibration and/or impact bruising damage during packing or transportation. This study shows that 1-MCP controls the senescence disorders, retards FF and green color losses, and reduces FD of ‘Bartlett’ pear after long-term storage through inhibiting ethylene production as previously observed (Calvo and Sozzi, 2009; DeEll and Ehsani-Moghaddam, 2011; Ekman et al., 2004; Feng et al., 2004; Trinchero et al., 2004; Villalobos-Acuña et al., 2011a,b). These results, however, indicate that the response of the PNW ‘Bartlett’ pear to 1-MCP is affected by fruit maturity, production elevation, and the holding temperature between harvest and 1-MCP treatment during storage room filling, which may result in its inconsistent efficacy in commercial application. FF is currently the commercial indicator of harvest timing for European pears in the PNW. Harvest starts when FF reaches 83.6 N and completes at 74.8 N, within 10–14 d in the growing region for ‘Bartlett’ (Chen, 2004; Wang et al., 2015). We found that 1-MCP had its highest efficacy on controlling the disorders of fruit harvested at the early commercial harvest maturity and least efficacy on fruit harvested at late maturity. Accordingly, IEC was not detected in the early harvested fruit, but accumulated in the late harvested fruit. It is reported that 1-MCP efficacy on ripening/senescence inhibition of climacteric fruit is affected by harvest maturity, with a reduced efficacy on more mature fruit (Chiriboga et al., 2013; Gamrasni
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Fig. 4. Fruit ripening capacity expressed as flesh firmness (FF) of 1-MCP treated ‘Bartlett’ pears on day 7 (A and B) and 12 at 20 C affected by harvest maturity (H1, H2) and production elevation (E1, E2) following storage at 1.1 C for 3, 5, and 6 months. Values are means SD.
et al., 2010; Jung and Watkins, 2014; Macnish et al., 2012; Mir et al., 2001; Villalobos-Acuña et al., 2011a,b; Watkins, 2008). The increase of IEC in more mature fruit at the time of treatment reduces a delay of tomato or avocado ripening by 1-MCP (Zhang et al., 2009, 2010, 2011). The increased ethylene production or IEC possibly reduce the competitive ability of 1-MCP molecules to bind to available receptors in climacteric fruit (Sisler and Serek, 1997). In the PNW, ‘Bartlett’ pear is produced at a range of elevations (from 100 m to 600 m in the Mid-Columbia area). We found that fruit harvested from different elevations (150 m and 610 m) with the same FF at a late harvest maturity (74.8 N) accumulated different levels of IEC. Fruit from the higher elevation accumulated higher IEC and lost its response to 1-MCP with respect to maintaining FF and green color and controlling storage disorders. The location where ‘Bartlett’ pears are grown has been shown to be an important factor affecting ethylene production and storage disorders (Agar et al., 1999; Whitaker et al., 2009). Ethylene production increased in ‘Bartlett’ pears that experienced cooler preharvest temperatures (Agar et al., 1999; Wang et al., 1971). Therefore, the fruit produced in higher elevations with cooler preharvest temperatures should be harvested in earlier maturity stages to avoid losing 1-MCP efficacy. The soil may also affect the fruit physiology and especially the ability of the fruit to regulate ethylene production. This could be another factor which can result in differences in response to 1-MCP treatment for fruit grown in different orchards. This may also suggest that FF may not be an accurate indicator of physiological status related to fruit maturity as suggested by Sugar and Basile (2013) and Villalobos-Acuña et al. (2011a), and that other factors including weather and tree management may influence fruit response to 1-MCP treatment. It typically takes 7–12 d to fill a pear storage room in the PNW until 1-MCP treatment can be carried out. The holding temperature during a 12 d delay between harvest and 1-MCP treatment affected
IEC accumulation, and therefore, 1-MCP efficacy on extending storage life of ‘Bartlett’ pear. A holding temperature at 5.0 C for 12 d increased IEC accumulation to a level that reduced 1-MCP efficacy on inhibiting senescence and controlling storage disorders of the PNW ‘Bartlett’ pear. Furthermore, ethylene production rate was increased in the fruit stored at 5 C for 12 d. Villalobos-Acuña et al. (2011a) reported that exogenous ethylene as little as 0.3 mL L 1 in the 1-MCP treating environment significantly reduced 1-MCP efficacy in ripening inhibition of ‘Bartlett’ pear. Therefore, a fast pre-cooling immediately after harvest and holding fruit at low temperature (i.e., 0 C) before 1-MCP treatment are necessary to prevent or reduce IEC accumulation and maximize 1-MCP efficacy on ‘Bartlett’ pear. European pears are resistant to ripening after harvest, however, they are enjoyed by consumers when fruit have ripened to a buttery and juicy texture at warm temperatures in 5–7 d depending on cultivar (Chen, 2004; Villalobos-Acuña and Mitcham, 2008). A period of cold storage or ethylene conditioning induces European pears ethylene synthesis and development of ripening capacity (Villalobos-Acuña and Mitcham, 2008; Makkumrai et al., 2014). 1-MCP treatment inhibits ‘Bartlett’ pear ethylene synthesis and controls storage disorders, which, unfortunately, reduces the ripening capacity as previously reported in European pears (Argenta et al., 2003; Bai et al., 2006; Chen and Spotts, 2005; Chiriboga et al., 2013; Villalobos-Acuña et al., 2011a; Xie et al., 2014). The optimum firmness for an ideal eating quality of European pears with buttery and juicy texture ranges between 14 and 23 N (Chen et al., 2003; Kappel et al., 1995). In this study, all the 1-MCP treated ‘Bartlett’ pears did not develop ripening capacity before 3 months of cold storage. The 1-MCP treated E1H1, E1H2, and E2H1 fruit developed certain degree of ripening capacity after 5 or 6 months of storage, but took 10–14 d to ripen to FF < 23 N.
Table 2 Effect of holding temperature during a 12 d delay between harvest and 1-MCP treatment on internal ethylene concentration and ethylene production rate of ‘Bartlett’ pears harvested at FF = 80.0 N from E1. Holding condition
Internal ethylene concentration (mL L
At harvest 12 d at 0 C 12 d at 5 C
0 0 0.59 0.38
Values are means SD.
1
)
Ethylene production rate (ng kg 0 0 2.5 1.1
1
s
1
)
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Fig. 5. Fruit flesh firmness (FF), peel chlorophyll content, senescent scald (SS), and senescent core breakdown (SCB) of 1-MCP treated ‘Bartlett’ pears affected by holding temperature during a 12 d delay between harvest and 1-MCP treatment after storage at 1.1 C for 6 months. Values are means SD. Different letters indicate significant differences between treatments at each assessment according to Fisher’s protected LSD test at p = 0.05.
5. Conclusion 1-MCP can extend the packing season and prevent storage disorders of ‘Bartlett’ pear. To ensure a consistent efficacy in commercial application, any factors affecting ethylene production or the physiological maturity stage at the time of 1-MCP treatment should be taken into consideration. These factors have been identified as harvest maturity, production elevation, and holding temperature between harvest and 1-MCP treatment. However, a continuing challenge for commercializing 1-MCP on European pears is how to ripen the 1-MCP treated fruit to their ideal eating quality in about 7 d at room temperature following cold storage. More research is warranted to investigate conditioning technologies such as moderate warm temperatures and ethylene conditioning to adequately ripen 1-MCP treated European pears. Acknowledgements We are grateful to the Columbia Gorge Fruit Growers Association, the PNW Pear Research Committees, and the Oregon State Agricultural Experiment Station for financial support. References Agar, I.T., Biasi, W.V., Mitcham, E.J., 1999. Exogenous ethylene accelerates ripening responses in Bartlett pears regardless of maturity or growing region. Postharvest Biol. Technol. 12, 67–78. Argenta, L.C., Fan, X.T., Mattheis, J.P., 2003. Influence of 1-methylcyclopropene on ripening storage life, and volatile production by ‘d’Anjou' cv. pear fruit. J. Agric. Food Chem. 51, 3858–3864. Bai, J., Mattheis, J.P., Reed, N., 2006. Re-initiating softening ability of 1methylcyclopropene-treated ‘Anrtlett’ and ‘d’Anjou' pears after regular air or controlled atmosphere storage. J. Hortic. Sci. Biotechnol. 81, 959–964. Calvo, G., Sozzi, G.O., 2009. Effectiveness of 1-MCP treatment on ‘Bartlett’ pears as influenced by the cooling method and the bin material. Postharvest Biol. Technol. 51, 49–55.
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