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Storage disorder and ripening behavior of ‘Doyenne du Comice’ pears in relation to storage conditions
Postharvest Biology and Technology 28 (2003) 281 /294 www.elsevier.com/locate/postharvbio
Storage disorder and ripening behavior of ‘Doyenne du Comice’ pears in relation to storage conditions Shu Shang Ma a, Paul M. Chen b,* b
a College of Horticulture, Northwest Sci-Tech University of Agriculture and Forestry, Yangling, Shaanxi 712100, China Mid-Columbia Agricultural Research and Extension Center, Oregon State University, 3005 Experiment Station Drive, Hood River, OR 97031-9512, USA
Received 26 February 2002; accepted 25 August 2002
Abstract ‘Doyenne du Comice’ pears (Pyrus communis , L.) harvested at commercial maturity with flesh firmness (FF) of 55.1 N (9/2.78 N) were stored in air and different controlled atmosphere (CA) conditions at /1 8C to evaluate storage disorder, ripening behavior and dessert quality after different storage intervals. Fruit stored in air developed both flesh breakdown (FB) and senescent scald (SCALD) disorders alter 4 months of storage. Incidence of FB and SCALD increased after 5 and 6 months of storage. Development of FB disorder in air-stored fruit was not associated with the activity of pyruvate decarboxylase (PDC) or alcohol dehydrogenase. Changes in a-farnesene and conjugated trienes in the peel tissue were highly associated with the development of SCALD. CA-stored fruit were free from SCALD disorder regardless of CA regime and storage time but developed internal browning (IB) disorder after 4 months of storage. Incidence of IB increased after 5 and 6 months of CA storage. Fruit stored in 0.5 and 1% O2 suffered higher incidence of IB than those stored in 1.5 and 2.0% O2. Symptoms of CA-induced IB are different from those of FB disorder, which resulted from prolonged air storage. The development of IB disorder was closely associated with an increase in PDC activity. Changes in ethylene production and FF during post-storage ripening at 20 8C were found to be the best objective measurements of storage life of ‘Doyenne du Comice’ fruit. Fruit stored in refrigerated air for 1 /3 months exhibited typical climacteric-like patterns of ethylene production during 15 days at 20 8C and softened to proper ripeness with desirable eating quality on day 5 at 20 8C. The magnitude of ethylene production increased with storage time when initially transferred to temperature at 20 8C. Fruit stored in air for 4 months or longer did not exhibit climacteric-like patterns of ethylene production during ripening and softened improperly with coarse and dry texture. Fruit stored in either 1% O2/B/0.1% CO2 or 2% O2/1% CO2 for 3 months (short-term CA storage) followed by holding in air at /1 8C for 1, 2, and 3 months were capable of ripening normally with desirable dessert quality without developing any physiological disorders. Short-term CA storage 4 of ‘Comice’ fruits maintained green skin color during 3 months of holding in air at /1 8C. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Alcohol dehydrogenase; Controlled atmosphere storage; Dessert quality; Ethylene production; Extractable juice; Flesh breakdown; Flesh firmness; Internal browning; Pyrus communis ; Pyruvate decarboxylase; Soluble solids concentration; Titratable acids
* Corresponding author. Tel.: /1-541-3862030; fax: /1-541-3861905 E-mail address: [email protected] (P.M. Chen). 0925-5214/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 ( 0 2 ) 0 0 1 7 9 - 5
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1. Introduction ‘Doyenne du Comice’ (denoted as ‘Comice’ hereafter) pear is the third most important winter pear cultivar grown in the Pacific Northwest of the United States. Because of its unique eating quality that is often considered superior to the most available pear cultivars, ‘Comice’ pears are often found in gift boxes and fruit baskets during the winter holiday season. Much of the research on storage conditions and quality preservation of ‘Comice’ pears has been conducted in pear growing regions outside of the United States (Bertolini and Casadei, 2000; Eccher-Zerbini et al., 1993, 1996, 1997; Elgar et al., 1997; Garcia and Streif, 1993; Geeson et al., 1991; Gram and Ruck, 1985; Kellerhals et al., 1991; Lammertyn et al., 2000; Leblond, 1986; Roelofts and Van Hermon, 1994; Shcherbatko and Korzhov, 1985; Schwarz, 1990; Smith et al., 1991). Hansen and Mellenthin (1979) have stated that the optimum harvest maturity for ‘Comice’ pears grown in the Pacific Northwest of America is when the flesh firmness (FF) falls to between 57.8 N (13 lb) and 48.9 N (11 lb); the optimum storage temperature is at /1 8C (308F); and the maximum storage period is between 120 and 130 days in conventional air storage at /1 8C These statements might be based on practical experience since no literature was cited (Hansen and Mellenthin, 1979). Further literature regarding storability and ripening behavior of ‘Comice’ pears grown in the Pacific Northwest are not available. The purpose of this study was to examine storage life and ripening behavior of ‘Comice’ pears grown in Hood River Valley, OR, as influenced by different storage conditions. The specific objectives of this study were: (1) to investigate storage disorder and ripening behavior of ‘Comice’ pears following refrigerated air storage; (2) to study effect of different controlled atmosphere (CA) regimes and storage time on storage disorder of ‘Comice’ pears; and (3) to examine ripening behavior and storage disorder of ‘Comice’ pears after short-term CA storage. Activity of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) was assayed to determine the possible role of anaerobic respiration in association with the development of flesh
browning and/or internal browning (IB) disorder. Changes in a-farnesene (FAR) and conjugated trienes (CT) in the peel tissue were also measured to assess the possible cause of senescent scald (SCALD) disorder in relation to the oxidation of FAR in ‘Comice’ pear skin after refrigerated storage. Our goal was to provide the pear industry with useful scientific information on the optimum storage conditions for extending he marketing season of this pear cultivar.
2. Materials and methods 2.1. Storage disorder and ripening behavior of ‘Comice’ pears following refrigerated air storage ‘Comice’ pears were harvested at commercial maturity with FF of 55.1 N (9/2.8 N) from an orchard block of mature trees in Hood River, OR, on 27 September 1998. Harvested fruit were transferred into 20-kg wooden boxes with perforated polyethylene liners (20.3 mm in thickness) (a total of 21 boxes), and stored at /1 8C in air. After 1, 2, 3, 4, 5, and 6 months of storage, three boxes of fruit were removed from the cold storage and held at 20 8C to study ripening behavior. At the beginning of each sampling interval (i.e. on day 0 of ripening at 20 8C), 5 fruit per replicate (box) were weighed and transferred into a respiration chamber. Each chamber was sealed and supplied with constant airflow (200 ml min 1 flow rate). The rate of ethylene production from each replicated fruit sample was determined daily for 15 d by a gas chromatograph according to previously described methods (Chen and Mellenthin, 1981). At the beginning of each sampling interval, another 5 fruit were used to extract soluble proteins from pulp tissues for assaying activity of PDC and ADH. One wedged sector of fruit pulp tissue including skin was sliced from the cheek area of each fruit. A composite 5-g pulp tissue sample was homogenized in 20 ml of extraction buffer for 20 s using a polytron homogenizer (Brinkmann Instruments, New York). The extraction buffer contained 100 (mmol l 1) 2-(N -morpholino)-ethanesulfonic acid (pH 6.5) and 5 (mmol l 1) dithiothreitol and 0.5% soluble poly-
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vinylpyrrolidone. The homogenate was filtered through four layers of cheesecloth and centrifuged at 27 000 /g for 10 min. All extraction procedures were conducted at 4 8C. The supernatant was stored at /72 8C until used for the assay of PDC and ADH activities using the method of Chang et al. (1982), modified by Nanos et al. (1992). On days 1, 3, 5 and 7 of post-storage ripening (stated as ‘ripening’ hereafter), 10 fruit (designated as an experimental unit) from each of 3 replicated boxes were used to determine FF by UC pressure tester with an 8-mm plunger at two locations per fruit (Chen and Mellenthin, 1981). For determination of extractable juice (EJ), soluble solids content (SSC) and titratable acids (TA), fruit used for determination of FF were peeled and sliced, and 0.1 kg of flesh tissue was juiced in a juice extractor (Acme Model 6001) for 1 min (Chen and Mellenthin, 1981). EJ was measured in a 100-ml graduated cylinder and expressed on a fresh weight basis as ml kg 1. SSC was read by a hand refractometer (Atago, NSG Precision Cells, Inc., Hicksville, NY). TA was determined by titrating 10 ml of juice to pH 7.2 using 0.1 N NaOH and calculated as mmol l 1 (Chen and Mellenthin, 1981). On day 5 of ripening, the dessert quality of ripened fruit including flesh texture and flavor (acid/ sugar balance and aroma) were rated on a nine-point hedonic scale with 9 /buttery and juicy texture with full flavor and 1 /coarse or mealy and dry texture with off flavor (McBride, 1986). The dessert quality was evaluated on 5 individual fruit by an in-house penal of five experienced assessors including the authors. Scale anchor points and definitions were determined in an orientation session which took place prior to the first evaluation in a controlled ‘discussion roam’ (Elgar et al., 1997). Each assessor tasted organoleptically one small fruit sector sliced from each fruit. The averaged scores of texture or flavor quality from each individual fruit assessed by five assessors were used for the statistical analyses. In addition, storage disorders (expressed as percentage of affected fruits) including flesh breakdown (FB) and SCALD were also assessed on day 5 of ripening. Each fruit was assessed visually and classified as ‘ycs’ or ‘no’ disorder regardless of
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the degree of severity. On day 5 of ripening, another 5 fruit per replicate were also weighed and used for analyses of FAR and CT according to Chen et al. (1990). A split-plot analysis of variance (ANOVA) was used for statistical analysis to determine the effect of storage time on ethylene productions and FF where monthly storage intervals were considered as the main plot and days of ripening as the subplot. If months of storage and days of ripening were found to be significantly different and to have a significant interaction, changes in ethylene productions or FF (dependent variable) were plotted against days of ripening (independent variable) for each monthly storage interval. For ethylene production, the smooth curves were employed and means among data points were separated by the least significant difference at the 5% level (LSD0.05) since the curves exhibited with different patterns to each other. For FF, the natural logarithmic function gave the best fit for each monthly fruit-softening curve. Another splitplot ANOVA was used for statistical analysis to determine the effect of storage time on EJ, TA 8 and soluble solids concentration (SSC) where monthly storage intervals were also considered as the main plot and the state of ripeness as the subplot. One-way ANOVA was used for statistical analyses of the activities of PDC and ADH, and the concentrations of FAR and CT. Means among each measurement (i.e., EJ, TA, SSC, PDC, ADH, FAR and CT) were separated by the LSD0.05. In the case of storage disorder and dessert quality, only means9/standard deviation (SD) were presented since they did not follow the Gaussian normal distribution (Steel et al., 1997). 2.2. Effect of different CA regimes and storage time on storage disorder of ‘Comice’ pears ‘Comice’ pears harvested from the same orchard block at the same date in 1998 as described in the previous section were drenched with 2-(4-thiazolyl) benzimidazole (TBZ) (Mertect 340-F, Syngenta Professional Products, Greensboro, NC) fungicide solution at the labeled concentration. After fungicide treatment, treated fruit were transferred into 64 18-kg bins with 20.3-mm perforated polyethy-
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lene liners. Four bins with packed ‘Comice’ fruit were loaded into each of 16 gas-tight CA cabinets within 10 d after the harvest date and cooled to temperature of /1 8C. Each cabinet was then sealed and flushed with N2 until O2 concentration in each cabinet was reduced to the desired level. The CA regime of each cabinet was established within 5 d after sealing. Concentrations of O2 and CO2 established for each cabinet were as follows: Cabinets Cabinets Cabinets Cabinets
1/4 0.5% O2/0.03% CO2 (lime) 5/8 1.0% O2/0.03% CO2 (lime) 9/12 1.5% O2/0.5% CO2 13/16 2.0% O2/1.0% CO2
The concentration of CO2 in cabinets 1 through 8 was maintained between 0.03 and 0.1% by using hydrated lime with a ratio of 1 kg lime per 20 kg fruit. Different O2 and CO2 concentrations were obtained by mixing cylinders of synthetic air, prepurified N2 and CO2 after each cabinet had been flushed with N2. Two-stage regulators were used to regulate each type of gas that was mixed in a mixing tube. The desirable mixed gas was delivered into each CA cabinet with a flow rate of approximately 50 ml min 1. This flow rate provided a change in atmosphere in each cabinet about every 4 h. The gas mixture was not humidified in order to prevent Tygon tubings from blockage due to ice formation. Concentrations of O2 and CO2 in each cabinet were monitored daily by a Servomex analyzer (Series 1400, Norwood, MA). After 3, 4, 5 and 6 months of storage, ‘Comice’ fruit in one cabinet of each CA regime were returned to air storage at /1 8C, After 1 month of holding in refrigerated air, four bins of fruit from each CA regime were transferred to a ripening room at 20 8C. On day 5 of ripening, fruit from each bin were used for assessment of storage disorders including IB and SCALD. Each fruit was assessed visually and classified as ‘yes’ or ‘no’ disorder regardless of degree of severity, Incidence of IB or SCALD disorder was expressed as percentage of affected fruits. On day 1 of ripening, 5 fruit from each bin were used to extract protein, which was used for assay of PDC and ADH activity as described in Section 2.1.
One-way ANOVA was used for statistical analyses of the activity of PDC and ADH. Means9/SD were used to compare the differences in incidences of storage disorder. 2.3. Ripening behavior and storage disorder of ‘Comice’ pears after short-term CA storage ‘Comice’ pears were harvested from the same orchard block as described in the previous section on 25 September 1999 when FF decreased to 54.5 N (9/2.2 N). Harvested fruit were drenched with TBZ fungicide solution at the labeled concentration. After fungicide treatment, treated fruit were transferred into 18 18-kg yellow bins with 20.3-mm perforated polyethylene liners. Three bins with packed ‘Comice’ fruit were loaded into each of six gas-tight CA cabinets within 10 d after harvest and cooled to temperature of /1 8C. Each cabinet was then sealed and flushed with N2 until the O2 concentration in each cabinet was reduced to the desired level. The CA regime of each cabinet was established within 5 d after sealing. The concentrations of O2 and CO2 established for each cabinet were as follows: Cabinets l/3 1.0% O2/0.031% CO2 (lime) Cabinets 4 /6 2.0% O2/1.0% CO2 After 3 months of CA storage, ‘Comice’ fruits were returned to air storage at /1 8C. In this experiment, each cabinet in each CA treatment was considered as a replicate. Therefore, each CA treatment had three replicates. After holding in air at /1 8C for 1, 2 and 3 months, one bin of fruit from each cabinet of each CA regime was transferred to a ripening room at 20 8C. At the beginning of each sampling interval (i.e. on day 0 of ripening at 208), 5 fruit per replicate were weighed and transferred into a respiration chamber supplied with constant airflow at the rate of 200 ml min 1. The rate of ethylene production from each replicated fruit sample was determined daily for 15 d by a gas chromatograph (Chen and Mellenthin, 1981). On day 1, 3, 5 and 7 of ripening, 10 fruit (designated as an experimental unit) from each of three replicated bins were used for determination of FF, EJ, SSC and TA by the
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Table 1 Activity of PDC and ADH, concentration of FAR and CT and incidence of FB and SCALD of ‘Comice’ pears after air storage at /1 8C Storage month
PDC mmol kg min
ADH 1
mmol kg min
FAR 1
mmol m
CT 2
mmol m
1 2 3 4 5 6
0.28 0.44 0.28 0.42 0.33 0.45
0.28 0.24 0.19 0.28 0.33 0.30
29 49 65 78 89 87
1 7 14 21 30 53
LSD.05 Source DFa Storage interval 5
/ Significance NS
/
14
6
NS
**
***
Incidence (%) 2
FB
SCALD
0 0 0 5.49/2.7 36.59/3.3 54.19/4.8
0 0 0 2.69/1.2 26.99/2.4 41.49/4.6
Protein extraction for PDC and ADH activity assay was performed at the beginning of each sampling interval. FAR, CT, FB and SCALD were assessed on day 5 of ripening at 20 8C after each storage interval. NS, **, ***not significant, significant at P /0.01, or at P /0.001, respectively. a DF, Degree of freedom.
methods as described in Section 2.1. On day 5 of ripening, dessert quality of ripened fruit including flesh texture and flavor (acid/sugar balance and aroma) was rated on a nine-point hedonic scale as described in Section 2.2. In addition, incidence (percentage of affected fruits) of storage disorders including IB and SCALD was assessed on day 5 of ripening. A three-way split-plot ANOVA was used for statistical analysis to determine the effect of CA regimes and monthly holding on ethylene production and fruit softening during ripening. In this case, different CA regimes were considered as the main plot, monthly holding as the sub-plot, and days of ripening as the sub-sub-plot. For ethylene production, smooth curves were employed and means among data points were separated by the LSD0.05 while the natural logarithmic function was the best fit for each monthly fruit-softening curve. Other data including EJ, TA and SSC were also subjected to a three-way split-plot ANOVA where different CA regimes were considered as the main plot, monthly holding as the sub-plot, and the state of ripeness as the sub-sub-plot. Means among each measurement were separated by the LSD0.05.
3. Results and discussion 3.1. Storage disorder and ripening behavior of ‘Comice’ pears after air storage Air-stored‘Comice’ fruit developed minor incidents of FB and SCALD disorders after 4 months of storage (Table 1). The symptom of FB includes softening and browning of cortex and core tissues, usually moist with offensive flavor. The symptom of FB does not resemble the symptom of senescent breakdown of apple fruit described by Porritt et al. (1982). They described senescent breakdown as ‘softening and browning of affected areas of cortex tissue, usually dry and poorly defined.’ Incidents of FB and SCALD increased to over 25% that were considered as commercially unacceptable after 5 and 6 months of storage (Table 1). Activity of PDC and ADH in air-stored fruits changed very little throughout 6 months of storage and were not associated with the development of FB disorder. Both FAR and CT concentrations in the peel tissue increased constantly during 6 months of storage with a second degree of polynomial equation as the best fit (FAR / /0.002 /
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Table 2 EJ, (ml kg 1), TA, (mmol l 1), SSC, (%) and dessert quality ratings (score 1-9) of ‘Comice’ pears after 6 monthly storage intervals in air at /1 8C Storage (months)
EJ
TA
SSC
Quality ratings
Unripe
Ripe
Unripe
Ripe
Unripe
Ripe
Texture
Flavor
1 2 3 4 5 6
698 718 712 695 695 687
473 487 570 660 674 671
26.7 24.6 21.2 18.5 19.5 16.8
25.9 20.7 20.0 18.3 19.8 16.9
13.8 14.1 14.1 13.9 13.9 13.7
14.1 14.5 14.5 13.8 13.2 13.6
8.19/0.6 8.39/0.5 8.39/0.6 5.79/0.6 4.39/0.6 3.19/0.7
4.29/0.4 7.19/0.5 8.49/0.5 5.39/0.3 3.79/0.3 3.69/0.4
LSD.05 Source (DF)a S(5) R (1) S /R (5)
34 Significance * ** **
4.l
0.4
** NS NS
NS NS NS
Unripe and ripe fruit refer to the fruit that had been transferred to a ripening room at 20 8C for 1 day or 5 days, respectively. Dessert qualities were assessed on day 5 at 20 8C. NS, not significant; * significant at P /0.05; ** significant at P /0.01. a S, Storage interval; R, ripe or unripe fruit; DF, degree of freedom.
(DS)2/0.801 /(DS)/6.710 (r2 /0.9854); CT / 0.0006 /(DS)2/0.134 /(DS)/2.986 (r2 / 0.9788); where DS represents days in storage and r2 is the correlation coefficient of determination). Therefore, changes in FAR and CT were associated with the development of SCALD disorder (Table 1). Oxidation of a FAR to CT was found to he the cause of superficial scald disorder of ‘d’Anjou’ pears (Chen et al., 1990). The magnitudes of FAR and CT in ‘Comice’ pears, however, were about 5 and 6 times, respectively, less than those in ‘d’Anjou’ pears at each corresponding storage interval (Chen et al., 1990). These data indicated that the biochemical basis of SCALD disorder of ‘Comice’ pears must be somewhat similar to that of superficial scald disorder of ‘d’Anjou’ pears. EJ of fruit stored between 1 and 3 months declined significantly from about 700 ml kg 1 to less than 570 ml kg 1 upon ripening while EJ of fruit stored for 4 months of longer clanged very little (Table 2). The reduction of EJ in ripened fruit was directly associated with the high texture quality, which was scored /8.0 (Table 2). Reduction of EJ is due to an increase in water-soluble pectin in the ripened flesh tissue, which increases the hygroscopic binding capacity (Chen and Bor-
gic, 1985). Ripened flesh tissue with EJ of B/600 ml kg 1 would have a very juicy texture. Although fruit stored for 1 month could ripen with the high texture quality, the flavor quality was scored as low as 4.2 (Table 2). Flavor quality of ripened fruit improved to the highest score after 3 months of storage and then decreased quickly after 4 months of storage or longer (Table 2). The results imply that the increase in aroma flavor in ‘Comice’ pears require a longer period of storage as compared to the development of juicy texture upon ripening. A prolonged storage period ( /4 months) caused ‘Comice’ pears to develop undesirable off flavor upon ripening. TA of fruit decreased consistently during 6 months of storage but there were no significant differences in TA between unripe and ripe fruit (Table 2). Malic acid, the main organic acid found in pear fruit, might have been used as the carbon source in the tricarboxylic acid cycle as part of the respiratory process, resulting in a decrease in TA concentration in winter pear cultivars during storage (Chen et al., 1982). SSC in fruit remained between 13.2 and 14.5% regardless of storage time and state of ripeness (Table 2). Changes in ethylene production and fruit softening during ripening at 20 8C were found to be
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287
Fig. 1. Ethylene production (EP) of ‘Doyenne du Comice’ pears on transfer to 20 8C after removal from refrigerated storage in air at /1 8C for 0, 1, 2, 3, 4, 5 and 6 months.
the best objective measurements of storage life of ‘Comice’ fruit. When ‘Comice’ pears were held at 20 8C for 15 or 7 d after each monthly storage interval at /1 8C, they exhibited different patterns of ethylene production and fruit softening, respectively (Figs. 1 and 2). ‘Comice’ fruit could not produce any measurable amount of ethylene to induce normal ripening without exposure to chilling at /1 8C, as expected of winter pears (Leblond and Ularich, 1973; Drouet and Hartmann, 1979; Blankenship and Richardson, 1985; Morin et al., 1985; Knee, 1987). The amount of chilling required is influenced by storage temperature (Sfakiotakis and Dilley, 1974; Gerasopoulos and Richardson, 1995). As chilling duration increased at /1 8C, the magnitude of ethylene production increased on day 1 of ripening at 20 8C and the number of days required to reach the climacteric-like peak of ethylene production was reduced (Fig. 1). Ethylene production of fruit stored for 4 months or longer progressively decreased without showing the distinctive climacteric-like peak during 15 d of ripening at 20 8C (Fig. 1). Similar ethylene production patterns were reported in ‘d’Anjou’ pears (Chen et al., 1983; Gerasopoulos and Richardson, 1997) and ‘Bose’
pears (Chen et al., 1995). Elgar et al. (1997) reported that ethylene production of ‘Comice’ pears increased with longer storage when initially transferred to higher temperature (i.e. day 1 at 20 8C), but tended to decline during ripening. However, their measurements of ethylene production in the ripening environment at 20 8C were only between day 1 and 7 upon removal from cold storage so that their data could not demonstrate the ethylene climacteric-like peak which occurred on day 8 or 9 of ripening. Nevertheless, our ethylene production data in the 7-day ripening period agreed with those reported by Elgar et al. (1997). In correspondence to ethylene production, ‘Comice’ pears were incapable of softening normally at 20 8C immediately after harvest indicating that a period of chilling was required for the induction of normal ripening capacity (data not presented). Fruit stored in air between 1 and 3 months softened swiftly to FF of 10 N on day 5 at 20 8C (Fig. 2). The optimum ripeness of ‘Comice’ pears for immediate eating was at FF between 10 and 20 N that occurred on day 5 of ripening at 20 8C. The ethylene climacteric peak that occurred on day 8 or 9 of ripening did not synchronize with
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Fig. 2. FF of ‘Doyenne du Comice’ pears on transfer to 20 8C after removal from refrigerated storage in air at /1 8C for 1, 2,3, 4, 5, 6 months. The (LSD.05) was 5.6 N. The regression equations are: (1 Mo) y / /21.9 ln(x )/49.9 r2 /0.970; (2 Mo) y / /21.7 ln(x )/ 47.3 r2 /0.975; (3 Mo) y / /22.7 ln(x )/45.3 r2 /0.983; (4 Mo) y / /8.8 ln(x )/37.6 r2 /0.824; (5 Mo) y / /6.4 ln(x )/36.6 r2 / 0.715; (6 Mo) y / /2.3 ln(x )/33.5 r2 /0.702.
the fruit-softening pattern (Figs. 1 and 2), a phenomenon similar to the ripening behavior of ‘d’Anjou’ pears (Chen et al., 1983). Fruit stored in air for 4 months or longer did not soften properly during ripening and remained firmer than 20 (N) on day 7 of ripening (Fig. 2). Based on the development of storage disorders and dessert qualities of ripened fruit combined with the profiles of ethylene production and fruitsoftening, the estimated storage life for ‘Comice’ fruit grown in Hood River Valley would be between 3 and 4 months when stored in air at / 1 8C. Elgar et al. (1997) reported that ‘Comice’ pears grown in New Zealand could develop optimum quality upon ripening when stored in air at /1 8C between 8 and 20 weeks after harvest. The storage life of ‘Comice’ pears grown in Germany was approximately 5 months when stored in air at 0 /0.5 8C and 95% RH (Gram and Ruck, 1985). Our study indicated that storage life of ‘Comice’ pears grown in Hood River Valley, OR was about 1 month less than those grown in New Zealand and Germany.
3.2. Effect of different CA regimes and storage time on storage disorder of ‘Comice’ pears Regardless of different CA regimes and the storage time, ‘Comice’ pears did not develop SCALD. CA-stored fruit maintained the original green skin color similar to the skin condition at harvest (personal observation). Fruit stored in different CA regimes for 3 months were also free from IB after 1 month of holding in refrigerated air plus 5 d of ripening at 20 8C (Table 3). Fruit stored in 0.5 and 1.0% oxygen CA started showing minor incidence of IB after 4 months of storage (Table 3). The symptom of IB includes the diffusive browning discoloration around the cortex tissue and the vascular bundles, usually dry and poorly defined. Occasionally, the core tissue is also affected. The symptom of IB induced by CA is distinctively different from the symptom of FB, which occurred in prolonged air storage. Incidence of IB increased to more than 11.3% when fruit were stored in different CA regimes for 5 month or longer, and was closely associated with oxygen
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Table 3 Incidence of SCALD and IB of ‘Comice’ pears following storage in different CA storages and 1 month in air at /l 8C plus 5 days at 20 8C Storage intervals
Type of disorder
0.5% O2 B/0.1% CO2
l.0% O2 B/0.1% CO2
1.5% O2 0.5% CO2
2.0% O2 1.0% CO2
3 months
SCALD IB
0% 0%
0% 0%
0% 0%
0% 0%
4 months
SCALD IB
0% 5.69/1.2%
0% 5.99/1.0%
0% 0%
0% 0%
5 months
SCALD IB
0% 29.89/9.7%
0% 20.79/7.3%
0% 15.69/3.2%
0% 11.39/3.0%
6 months
SCALD IB
0% 81.49/13.2%
0% 46.99/12.6%
0% 25.79/7.3%
0% 17.69/4.2%
concentration rather than carbon dioxide concentration in CA storage. Fruit stored in CA with lower oxygen concentration suffered higher incidence of IB (Table 3). After 3 months of storage, activity of PDC was 0.63, 0.74, 0.63 and 0.56 (mmol kg 1 min 1) in the pulp tissue of fruit stored in 0.5, 1.0, 1.5 and 2.0% O2, respectively while activity of ADH remained between 0.21 and 0.33 (mmol kg 1 min 1) regardless of CA regimes (Table 4). Activity of PDC in fruit increased
significantly between 4 and 6 months of storage, the lower the O2 concentration the higher the PDC activity (Table 4). Regardless of different CA regimes and the storage time, ADH activity changed very little (Table 4). Thus, development of IB might be induced by the increased PDC activity that resulted in the accumulation of acetaldehyde inside the pulp tissues. Our results suggested that PDC activity in ‘Comice’ pears was induced by the combination of low oxygen level
Table 4 Activity of PDC and ADH in ‘Comice’ pears following storage in different CA storages at /1 8 and 1 month in air plus 1 day at 20 8C Storage intervals
Activity (mmol kg 1 min 1)
0.5%O2 B/0.1% CO2
1.0% O2 B/0.1% 1.5%O2 0.5% CO2 CO2
2.0% O2 1.0% CO2
3 months
PDC ADH PDC ADH PDC ADH PDC ADH
0.63 0.21 0.84 0.26 1.94 0.30 2.15 0.32
0.74 0.27 0.87 0.22 l.72 0.28 1.94 0.25
0.56 0.30 0.62 0.31 0.83 0.33 1.71 0.32
4 months 5 months 6 months LSD.05 /0.14 (mmol kg 1 min 1) (PDC)
Significance a
Source (DF) S(3) CA (3) S /CA (9)
PDC ** * **
ADH NS NS NS
NS, not significant; * significant at P /0.05; ** significant at P /0.01. a S, storage interval; CA, CA regimes; DF, degree of freedom.
0.63 0.33 0.64 0.29 0.81 0.26 l.69 0.30
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Table 5 EJ, (ml kg 1), TA, (mmol l 1), SSC, (%) and dessert quality ratings (score 1 /9) of ‘Comice’ pears after 3 months of CA storage followed by l, 2 or 3 months in air at /l 8C CA regime
1% O2; B/0.03%CO2
2% O2; l% CO2
LSD.05 Source (DF)a CA (1) HD (2) R(1) CA /HD (2) Ca /R (1) HD /R (2) CA /HD /R
Holding (months)
1 2 3 1 2 3
EJ
TA
SSC
Quality ratings
Unripe
Ripe
Unripe
Ripe
Unripe
Ripe
Texture
Flavor
705 710 715 713 695 707
505 517 515 515 506 641
22.8 21.6 19.2 19.9 19.5 17.2
21.5 20.5 19.7 19.8 19.0 16.9
14.2 14.0 13.8 14.3 13.9 13.9
13.9 14.3 14.2 14.1 13.9 13.4
8.39/0.4 8.l9/0.7 7.89/0.5 7.79/0.6 8.39/0.5 5.19/4.4
7.29/0.5 8.19/0.3 7.79/0.6 7.39/0.4 7.79/0.6 6.69/0.7
34 Significance * * ** ** ** ** **
4.1 NS ** NS * NS NS NS
NS NS NS NS NS NS NS
Unripe and ripe fruit referred to fruit that had been transferred to a ripening room at 20 8C for 1 day or 5 days, respectively. Dessert qualities were assessed on day 5 at 20 8C. NS, not significant; * significant at P /0.05; ** significant at P /0.01. a CA, CA regimes; HD, holding period (months); R, ripening state; DF, degree of freedom.
and time of CA storage. Nanos et al. (1992) have suggested that removal of acetaldehyde is physiologically important, for the compound has long been known as a cause of physiological disorders in pears (Harley, 1927, 1929). It has been reported that acetaldehyde is more toxic than ethanol (Perata and Alpi, 1991). Roelofts and Van Hermon (1994) reported that ‘Doyenne du Comice’ pears stored at /0.5 8C in 2% oxygen with 0.2, 1.0 or 2.0% carbon dioxide maintained similar FF after 4 and 5 months while incidence of FB increased from nil up to an average of 9% after approximately 5 months of storage and 30% after approximately 6 months of storage. Their data indicated that incidence of FB was lowest in the lower carbon dioxide concentration and brown core disorder occurred with all CA storages even after approximately 4 months of storage and increased rapidly during post-storage ripening at room temperature. They did not define the symptoms of ‘FB’ disorder which presumably were similar to symptoms of ‘IB’ disorder described here.
3.3. Ripening behavior and storage disorder of ‘Comice’ pears after short-term CA storage ‘Comice’ pears stored either in 1.0% O2/ B/ 0.1% CO2 or in 2.0% O2/0.8% CO2 CA for 3 months were free from any storage disorders when the CA-stored fruit were held in air at /1 8C for 3 months plus 5 d of ripening at 20 8C (data not presented). Regardless of CA regime and holding period, there was a reduction of EJ when fruit were ripened (Table 5). Fruit stored in 1% O2 contained higher TA than those in 2% O2 but there was no difference in TA between unripe and ripe fruit (Table 5). SSC was not affected by treatment (Table 5). Both texture and flavor of ripe fruit scored above 7 on a nine-point hedonic scale except that overall dessert quality of 2% O2-stored fruit scored lower after 3 months of holding in refrigerated air (Table 5). Regardless of CA regime, patterns of ethylene production and fruit softening of CA-stored fruit resembled those of air-stored fruit that had been stored for 1 /3 months (Figs. 3 and 4). The results demonstrated
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291
Fig. 3. Ethylene production of ‘Comice’ pears during 15 days at 20 8C after 3 months of CA storage plus monthly holding intervals in refrigerated air (RA) at /1 8C.
that a short-term (i.e. 3 months) CA storage of ‘Comice’ pears extended the normal ripening capacity and maintained high dessert quality even after CA-stored fruit had been returned to refrigerated air storage for as long as 3 more months. Bertolini and Casadei (2000) also reported that low-O2 storage (1.5% O2/0.8% CO2) of Conference and Doyenne du Comice pears produced higher acidity, greener coloring and faster flesh softening during shelf-life than standard CA storage (3% O2/3% CO2). Garcia and
Streif (1993) assessed six pear cultivars for their suitability for CA storage using 3% O2/ B/1% CO2; 3% O2/3% CO2; 1% O2/ B/1% CO2; and 1% O2/3% CO2 at /1 8C. They concluded that Packham’s Triumph appeared to be the most suitable for CA storage, followed by Conference and Comice. They also indicated that both ‘Comice’ and ‘Packhams’ tolerated up to 3% CO2 while ultra-low O2 (ULO) concentration (1%) improved the keeping quality of these two cultivars.
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Fig. 4. FF of ‘Comice’ pears during 7 days at 20 8C after 3 months of CA storage plus monthly holding in refrigerated air (RA) at /1 8C.
In addition to the CA regimes discussed above, there have been other reports on the optimal CA regime for extending storage life of ‘Comice’ pears grown in different countries. Optimum CA regime for storage of pear cultivars including ‘Doyenne du Comice’ grown in Russia was found to be 8% O2 and 5% CO2 at 2 /3 8C (Shcherbatko and Korzhov, 1985). Recommended CA regime for storage of ‘Doyenne du Comice’ grown in France
was 5% O2 and 5% CO2 at 0 8C that could extend the storage life for 6 months (Leblond, 1986). In the present study, a CA regime with O2 level of 2% or lower could induce undesirable ‘IB’ disorder if ‘Comice’ pears were stored under these CA environments for longer than 3 months. It is evident that certain unknown environmental factors during fruit growth and maturation influence the optimum CA regime for extending storage life
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and avoiding storage disorders of ‘Comice’ pears grown in different regions.
4. Summary ‘Doyenne du Comice’ pears (Pyrus communis , L.) harvested at commercial maturity with FF of 55.1 N (9/2.8 N) from mature trees grown in the Hood River Valley, OR, ripened normally after 30 d of chilling at /10 8C. The storage life of ‘Comice’ pears in air at /1 8C was estimated about 4 month or shorter as judged by the criteria that the stored fruit remained free from any storage disorders, demonstrated a climacteric-like peak of ethylene production and were capable of softening properly with desirable dessert quality at 20 8C. Short-term (3 months) CA storage with 1% O2/ B/0.1% CO2 or 2% O2/1% CO2 could prevent ‘Comice’ pears from developing storage disorder and preserve the normal ripening behavior after they had been returned to air storage at /1 8C for as long as 3 months. This study provides the pear industry with useful information for marketing air-stored ‘Comice’ pears during the first 3 months after the fruit have satisfied the chilling requirement (:/1 month in air at /1 8C) followed by marketing short-term (3 months) CAstored fruit for another 3 months during the rest of marketing season.
Acknowledgements Oregon State Agricultural Experimental Station Technical Paper No. 11875. This study was supported by the Winter Pear Control Committee, USA.
References Bertolini, P., Casadei, C., 2000. Advances in pear storage technology. Rivista di Fruitticoltura e di Ortofloricoltura 62, 51 /54. Blankenship, S.M., Richardson, D.G., 1985. Development of ethylene biosynthesis and ethylene induced ripening in ‘d’Anjou’ pears during the cold requirement for ripening. J. Am. Soc. Hort. Sci. 110, 520 /523.
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Chang, L.A., Hammett, L.K., Pharr, D.M., 1982. Ethanol, alcohol dehydrogenase and pyruvate decarboxylase in storage roots of four sweet potato cultivars during simulated flood damage and storage. J. Am. Soc. Hort. Sci. 107, 674 /677. Chen, P.M., Mellenthin, W.M., 1981. Effect of harvest date on ripening capacity and postharvest life of ‘d’Anjou’ pears. J. Am. Soc. Hort. Sci. 106, 38 /42. Chen, P.M., Borgic, D.M., 1985. Changes in water-soluble polyuronides in the pulp tissue of ripening ‘Boss’ pears following cold storage in air or in 1% oxygen. J. Am. Soc. Hort. Sci. 110, 667 /671. Chen, P.M., Richardson, D.G., Mellenthin, W.M., 1982. Differences in biochemical composition between Beurre ‘d’Anjou’ and ‘Bose’ pears during fruit development and storage. J. Am. Soc. Hort. Sci. 107, 807 /812. Chen, P.M., Mellenthin, W.M., Borgic, D.M., 1983. Changes in ripening behavior of ‘d’Anjou’ pears (Pyrus communis , L.) after cold storage. Sci. Hort. 21, 137 /146. Chen, P.M., Varga, D.M., Mielke, E.A., Facteau, T.J., Drake, S.R., 1990. Control of superficial scald on ‘d’Anjou’ pears by ethoxyquin: oxidation of a-farnesene and its inhibition. J. Food Sci., 55, 171 /175, 180. Chen, P.M., Spotts, R.A., Varga, D.M., Cervantes, L.A., 1995. Ripening behavior and combined fungicide and prestorage heat effects on decay control of ‘Boat’ pears in air or stepwise low oxygen storage. Postharvest Biol. Technol. 6, 235 / 248. Drouet, A., Hartmann, C., 1979. Polyribosomes from pear fruit. Plant Physiol. 64, 1104 /1108. Eccher-Zerbini, P., Balzarotti, R., Rizzolo, A., Spada, G.L., 1993. Effect of picking date on quality and sensory characteristics of pears after storage and ripening. Acta Hort. 326, 291 /298. Eccher-Zerbini, P., Grassi, M., Perego, S., Spada, G.L., Liverani, C. and de Jager, A., 1996. Harvest index of Comice pears by a multivariate method, and relation to post-storage quality. COST 94. The Postharvest Treatment of Fruit and Vegetables. Determination and Prediction of Optimum Harvest Date of Apples and Pears. Proceedings of a Meeting, Lofthus, Norway, 9 /10 June 1994, 157 /164. Eccher-Zerbini, P., Grassi, M., Spada, G.L., Grazianetti, S., 1997. Sensory quality of pears of different harvest maturity after CA storage. Atti dell’Istituto Sperimentale per la Valorizzazione Tecnologica dei Prodotti Agricoli Milano 18, 141 /146. Elgar, H.J., Watkins, C.B., Murray, S.H., Gunson, F.A., 1997. Quality of ‘Buerre Bose’ and ‘Doyenne du Comice’ pear in relation to harvest date and storage period. Postharvest Biol. Technol. 10, 29 /37. Garcia, J.M., Streif, J., 1993. Quality and storage potential of pears. 1. Influence of CA and ULO-storage conditions. Gartenbau. 58, 36 /41. Geeson, J.D., Genge, P.M., Sharples, R.O., Smith, S.M., 1991. Limitations to modified atmosphere packaging for extending the shelf-life of partly ripened Doyenne du Comice pears. Int. J. Food Sci. Technol. 26, 225 /231.
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Gerasopoulos, D., Richardson, D.G., 1995. Change in fatty acids of ‘d’Anjou’ pears in relation to storage temperature and calcium. Acta Hort. 379, 459 /466. Gerasopoulos, D., Richardson, D.G., 1997. Ethylene production by ‘d’Anjou’ pears during storage at chilling and nonchilling temperature. Hort. Sci. 32, 1092 /1094. Gram, K.H., Ruck, A., 1985. Practical experience and results from the production and storage of pears. Gartenbau. 32, 243 /244. Hansen, F. and Mellenthin, W.M., 1979. Commercial handling and storage practices for winter pears. Special report 550, Agricultural Experiment Station, Oregon State University, pp. 12. Harley, C.P., 1927. The occurrence of acetaldehyde in Bartlett pears and its relation to pear scald and breakdown. J. Agric. Res. 35, 983 /993. Harley, C.P., 1929. Relation of picking time to acetaldehyde content and core breakdown of ‘Bartlett’ pears. J. Agric. Res. 39, 483 /493. Kellerhals, M., Fluckiger, A., Sulzer, Y., Lehmann, A., Krebs, C., 1991. Postharvest ripening of various pear cultivars. Schweizeriscbe Zeitschrifl fur Obst and Weinbau 127, 733 / 738. Knee, M., 1987. Development of ethylene biosynthesis in pear fruits at /1 8C. J. Exp. Bot. 38, 1724 /1733. Lammertyn, J., Verlinden, B., de Baerdemaeker, J., 2000. Relation between core breakdown disorder and storage conditions of Pyrus communis. Acta Hort. 518, 115 /120. Leblond, C., Ularich, R., 1973. Controle de l’evolution de la maturation par divers traitements theriques et gazeux chez la poire ‘Passe-Crassane’. Bull. Inst. Int. Froid. 3, 69 /74. Leblond, C., 1986. Pear quality. Results of 15 years of trials with AFCOFEL. Part II. Pear cultivar Doyenne du Comice and some varieties being tested in C orchards. Arboricult. Fruitiere 33, 34 /38.
McBride, R.L., 1986. Hedonic rating of food: single or side-byside sample presentation? J. Food Tech. 21, 355 /363. Morin, F., Rigault, C., Hartmann, C., 1985. Consequences d’ un sejour au froid sur le metabolisme de l’ethylene au cours de la maturation de la poire Passe Crassane apres recolte. Physiol. Veg. 23, 353 /359. Nanos, G.D., Romani, R.J., Kader, A.A., 1992. Metabolic and other responses of ‘Bartlett’ pear fruit and suspensioncultured ‘Passe Crassane’ pear fruit cells held in 0.25%. J. Am. Soc. Hort. Sci. 117, 934 /940. Perata, P., Alpi, A., 1991. Ethanol-induced injuries to carrot cells. Plant Physiol. 95, 748 /752. Porritt, S.W., Meheriuk, M., Lidster, P.D., 1982. Postharvest disorders of apples and pears. Agric. Can. Publ. 1737/E, 66. Roelofts, F.P.M.M., Van Hermon, E.A., 1994. Scrubbed CAstorage of Doyenne du Comice. CA-storage improves the quality, but does not lengthen the storage life. Fruitteelt Den Haag 84, 12 /13. Shcherbatko, D.M., Korzhov, V.V., 1985. Keeping quality and storage systems for the fruit of various pear varieties. Trudy po Prikladnoi Botanike Genetike i Selektsii 78, 23 /29. Schwarz, A., 1990. Trial of cold storage of pears in controlled atmospheres. II. Doyenne du Comice. Revue Suisse de Viticulture, d’Arboriculture et d’Horticulture 22, 265 /267. Sfakiotakis, E.M., Dilley, D.R., 1974. Induction of ethylene production in ‘Bose’ pears by preharvest cold stress. Hort. Sci. 97, 336 /338. Smith, S.M., Geeson, J.D., Genge, P.M., Sharples, R.O., 1991. The effects of modified atmosphere packaging and stage of ripeness on the quality of English pears during simulated marketing. Proceedings of the fifth international CA research conference, Wenatchee, WA, USA 14 /16 June 1989, Vol. 1, pp. 315 /324. Steel, R.G.D., Torrie, J.H., Dickey, D.A., 1997. Principles and Procedures of Statistics. A Biochemical Approach, third ed.. WCB McGraw-Hill, New York.
Storage disorder and ripening behavior of ‘Doyenne du Comice’ pears in relation to storage conditions Shu Shang Ma a, Paul M. Chen b,* b
a College of Horticulture, Northwest Sci-Tech University of Agriculture and Forestry, Yangling, Shaanxi 712100, China Mid-Columbia Agricultural Research and Extension Center, Oregon State University, 3005 Experiment Station Drive, Hood River, OR 97031-9512, USA
Received 26 February 2002; accepted 25 August 2002
Abstract ‘Doyenne du Comice’ pears (Pyrus communis , L.) harvested at commercial maturity with flesh firmness (FF) of 55.1 N (9/2.78 N) were stored in air and different controlled atmosphere (CA) conditions at /1 8C to evaluate storage disorder, ripening behavior and dessert quality after different storage intervals. Fruit stored in air developed both flesh breakdown (FB) and senescent scald (SCALD) disorders alter 4 months of storage. Incidence of FB and SCALD increased after 5 and 6 months of storage. Development of FB disorder in air-stored fruit was not associated with the activity of pyruvate decarboxylase (PDC) or alcohol dehydrogenase. Changes in a-farnesene and conjugated trienes in the peel tissue were highly associated with the development of SCALD. CA-stored fruit were free from SCALD disorder regardless of CA regime and storage time but developed internal browning (IB) disorder after 4 months of storage. Incidence of IB increased after 5 and 6 months of CA storage. Fruit stored in 0.5 and 1% O2 suffered higher incidence of IB than those stored in 1.5 and 2.0% O2. Symptoms of CA-induced IB are different from those of FB disorder, which resulted from prolonged air storage. The development of IB disorder was closely associated with an increase in PDC activity. Changes in ethylene production and FF during post-storage ripening at 20 8C were found to be the best objective measurements of storage life of ‘Doyenne du Comice’ fruit. Fruit stored in refrigerated air for 1 /3 months exhibited typical climacteric-like patterns of ethylene production during 15 days at 20 8C and softened to proper ripeness with desirable eating quality on day 5 at 20 8C. The magnitude of ethylene production increased with storage time when initially transferred to temperature at 20 8C. Fruit stored in air for 4 months or longer did not exhibit climacteric-like patterns of ethylene production during ripening and softened improperly with coarse and dry texture. Fruit stored in either 1% O2/B/0.1% CO2 or 2% O2/1% CO2 for 3 months (short-term CA storage) followed by holding in air at /1 8C for 1, 2, and 3 months were capable of ripening normally with desirable dessert quality without developing any physiological disorders. Short-term CA storage 4 of ‘Comice’ fruits maintained green skin color during 3 months of holding in air at /1 8C. # 2002 Elsevier Science B.V. All rights reserved. Keywords: Alcohol dehydrogenase; Controlled atmosphere storage; Dessert quality; Ethylene production; Extractable juice; Flesh breakdown; Flesh firmness; Internal browning; Pyrus communis ; Pyruvate decarboxylase; Soluble solids concentration; Titratable acids
* Corresponding author. Tel.: /1-541-3862030; fax: /1-541-3861905 E-mail address: [email protected] (P.M. Chen). 0925-5214/02/$ - see front matter # 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 5 - 5 2 1 4 ( 0 2 ) 0 0 1 7 9 - 5
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1. Introduction ‘Doyenne du Comice’ (denoted as ‘Comice’ hereafter) pear is the third most important winter pear cultivar grown in the Pacific Northwest of the United States. Because of its unique eating quality that is often considered superior to the most available pear cultivars, ‘Comice’ pears are often found in gift boxes and fruit baskets during the winter holiday season. Much of the research on storage conditions and quality preservation of ‘Comice’ pears has been conducted in pear growing regions outside of the United States (Bertolini and Casadei, 2000; Eccher-Zerbini et al., 1993, 1996, 1997; Elgar et al., 1997; Garcia and Streif, 1993; Geeson et al., 1991; Gram and Ruck, 1985; Kellerhals et al., 1991; Lammertyn et al., 2000; Leblond, 1986; Roelofts and Van Hermon, 1994; Shcherbatko and Korzhov, 1985; Schwarz, 1990; Smith et al., 1991). Hansen and Mellenthin (1979) have stated that the optimum harvest maturity for ‘Comice’ pears grown in the Pacific Northwest of America is when the flesh firmness (FF) falls to between 57.8 N (13 lb) and 48.9 N (11 lb); the optimum storage temperature is at /1 8C (308F); and the maximum storage period is between 120 and 130 days in conventional air storage at /1 8C These statements might be based on practical experience since no literature was cited (Hansen and Mellenthin, 1979). Further literature regarding storability and ripening behavior of ‘Comice’ pears grown in the Pacific Northwest are not available. The purpose of this study was to examine storage life and ripening behavior of ‘Comice’ pears grown in Hood River Valley, OR, as influenced by different storage conditions. The specific objectives of this study were: (1) to investigate storage disorder and ripening behavior of ‘Comice’ pears following refrigerated air storage; (2) to study effect of different controlled atmosphere (CA) regimes and storage time on storage disorder of ‘Comice’ pears; and (3) to examine ripening behavior and storage disorder of ‘Comice’ pears after short-term CA storage. Activity of pyruvate decarboxylase (PDC) and alcohol dehydrogenase (ADH) was assayed to determine the possible role of anaerobic respiration in association with the development of flesh
browning and/or internal browning (IB) disorder. Changes in a-farnesene (FAR) and conjugated trienes (CT) in the peel tissue were also measured to assess the possible cause of senescent scald (SCALD) disorder in relation to the oxidation of FAR in ‘Comice’ pear skin after refrigerated storage. Our goal was to provide the pear industry with useful scientific information on the optimum storage conditions for extending he marketing season of this pear cultivar.
2. Materials and methods 2.1. Storage disorder and ripening behavior of ‘Comice’ pears following refrigerated air storage ‘Comice’ pears were harvested at commercial maturity with FF of 55.1 N (9/2.8 N) from an orchard block of mature trees in Hood River, OR, on 27 September 1998. Harvested fruit were transferred into 20-kg wooden boxes with perforated polyethylene liners (20.3 mm in thickness) (a total of 21 boxes), and stored at /1 8C in air. After 1, 2, 3, 4, 5, and 6 months of storage, three boxes of fruit were removed from the cold storage and held at 20 8C to study ripening behavior. At the beginning of each sampling interval (i.e. on day 0 of ripening at 20 8C), 5 fruit per replicate (box) were weighed and transferred into a respiration chamber. Each chamber was sealed and supplied with constant airflow (200 ml min 1 flow rate). The rate of ethylene production from each replicated fruit sample was determined daily for 15 d by a gas chromatograph according to previously described methods (Chen and Mellenthin, 1981). At the beginning of each sampling interval, another 5 fruit were used to extract soluble proteins from pulp tissues for assaying activity of PDC and ADH. One wedged sector of fruit pulp tissue including skin was sliced from the cheek area of each fruit. A composite 5-g pulp tissue sample was homogenized in 20 ml of extraction buffer for 20 s using a polytron homogenizer (Brinkmann Instruments, New York). The extraction buffer contained 100 (mmol l 1) 2-(N -morpholino)-ethanesulfonic acid (pH 6.5) and 5 (mmol l 1) dithiothreitol and 0.5% soluble poly-
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vinylpyrrolidone. The homogenate was filtered through four layers of cheesecloth and centrifuged at 27 000 /g for 10 min. All extraction procedures were conducted at 4 8C. The supernatant was stored at /72 8C until used for the assay of PDC and ADH activities using the method of Chang et al. (1982), modified by Nanos et al. (1992). On days 1, 3, 5 and 7 of post-storage ripening (stated as ‘ripening’ hereafter), 10 fruit (designated as an experimental unit) from each of 3 replicated boxes were used to determine FF by UC pressure tester with an 8-mm plunger at two locations per fruit (Chen and Mellenthin, 1981). For determination of extractable juice (EJ), soluble solids content (SSC) and titratable acids (TA), fruit used for determination of FF were peeled and sliced, and 0.1 kg of flesh tissue was juiced in a juice extractor (Acme Model 6001) for 1 min (Chen and Mellenthin, 1981). EJ was measured in a 100-ml graduated cylinder and expressed on a fresh weight basis as ml kg 1. SSC was read by a hand refractometer (Atago, NSG Precision Cells, Inc., Hicksville, NY). TA was determined by titrating 10 ml of juice to pH 7.2 using 0.1 N NaOH and calculated as mmol l 1 (Chen and Mellenthin, 1981). On day 5 of ripening, the dessert quality of ripened fruit including flesh texture and flavor (acid/ sugar balance and aroma) were rated on a nine-point hedonic scale with 9 /buttery and juicy texture with full flavor and 1 /coarse or mealy and dry texture with off flavor (McBride, 1986). The dessert quality was evaluated on 5 individual fruit by an in-house penal of five experienced assessors including the authors. Scale anchor points and definitions were determined in an orientation session which took place prior to the first evaluation in a controlled ‘discussion roam’ (Elgar et al., 1997). Each assessor tasted organoleptically one small fruit sector sliced from each fruit. The averaged scores of texture or flavor quality from each individual fruit assessed by five assessors were used for the statistical analyses. In addition, storage disorders (expressed as percentage of affected fruits) including flesh breakdown (FB) and SCALD were also assessed on day 5 of ripening. Each fruit was assessed visually and classified as ‘ycs’ or ‘no’ disorder regardless of
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the degree of severity. On day 5 of ripening, another 5 fruit per replicate were also weighed and used for analyses of FAR and CT according to Chen et al. (1990). A split-plot analysis of variance (ANOVA) was used for statistical analysis to determine the effect of storage time on ethylene productions and FF where monthly storage intervals were considered as the main plot and days of ripening as the subplot. If months of storage and days of ripening were found to be significantly different and to have a significant interaction, changes in ethylene productions or FF (dependent variable) were plotted against days of ripening (independent variable) for each monthly storage interval. For ethylene production, the smooth curves were employed and means among data points were separated by the least significant difference at the 5% level (LSD0.05) since the curves exhibited with different patterns to each other. For FF, the natural logarithmic function gave the best fit for each monthly fruit-softening curve. Another splitplot ANOVA was used for statistical analysis to determine the effect of storage time on EJ, TA 8 and soluble solids concentration (SSC) where monthly storage intervals were also considered as the main plot and the state of ripeness as the subplot. One-way ANOVA was used for statistical analyses of the activities of PDC and ADH, and the concentrations of FAR and CT. Means among each measurement (i.e., EJ, TA, SSC, PDC, ADH, FAR and CT) were separated by the LSD0.05. In the case of storage disorder and dessert quality, only means9/standard deviation (SD) were presented since they did not follow the Gaussian normal distribution (Steel et al., 1997). 2.2. Effect of different CA regimes and storage time on storage disorder of ‘Comice’ pears ‘Comice’ pears harvested from the same orchard block at the same date in 1998 as described in the previous section were drenched with 2-(4-thiazolyl) benzimidazole (TBZ) (Mertect 340-F, Syngenta Professional Products, Greensboro, NC) fungicide solution at the labeled concentration. After fungicide treatment, treated fruit were transferred into 64 18-kg bins with 20.3-mm perforated polyethy-
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lene liners. Four bins with packed ‘Comice’ fruit were loaded into each of 16 gas-tight CA cabinets within 10 d after the harvest date and cooled to temperature of /1 8C. Each cabinet was then sealed and flushed with N2 until O2 concentration in each cabinet was reduced to the desired level. The CA regime of each cabinet was established within 5 d after sealing. Concentrations of O2 and CO2 established for each cabinet were as follows: Cabinets Cabinets Cabinets Cabinets
1/4 0.5% O2/0.03% CO2 (lime) 5/8 1.0% O2/0.03% CO2 (lime) 9/12 1.5% O2/0.5% CO2 13/16 2.0% O2/1.0% CO2
The concentration of CO2 in cabinets 1 through 8 was maintained between 0.03 and 0.1% by using hydrated lime with a ratio of 1 kg lime per 20 kg fruit. Different O2 and CO2 concentrations were obtained by mixing cylinders of synthetic air, prepurified N2 and CO2 after each cabinet had been flushed with N2. Two-stage regulators were used to regulate each type of gas that was mixed in a mixing tube. The desirable mixed gas was delivered into each CA cabinet with a flow rate of approximately 50 ml min 1. This flow rate provided a change in atmosphere in each cabinet about every 4 h. The gas mixture was not humidified in order to prevent Tygon tubings from blockage due to ice formation. Concentrations of O2 and CO2 in each cabinet were monitored daily by a Servomex analyzer (Series 1400, Norwood, MA). After 3, 4, 5 and 6 months of storage, ‘Comice’ fruit in one cabinet of each CA regime were returned to air storage at /1 8C, After 1 month of holding in refrigerated air, four bins of fruit from each CA regime were transferred to a ripening room at 20 8C. On day 5 of ripening, fruit from each bin were used for assessment of storage disorders including IB and SCALD. Each fruit was assessed visually and classified as ‘yes’ or ‘no’ disorder regardless of degree of severity, Incidence of IB or SCALD disorder was expressed as percentage of affected fruits. On day 1 of ripening, 5 fruit from each bin were used to extract protein, which was used for assay of PDC and ADH activity as described in Section 2.1.
One-way ANOVA was used for statistical analyses of the activity of PDC and ADH. Means9/SD were used to compare the differences in incidences of storage disorder. 2.3. Ripening behavior and storage disorder of ‘Comice’ pears after short-term CA storage ‘Comice’ pears were harvested from the same orchard block as described in the previous section on 25 September 1999 when FF decreased to 54.5 N (9/2.2 N). Harvested fruit were drenched with TBZ fungicide solution at the labeled concentration. After fungicide treatment, treated fruit were transferred into 18 18-kg yellow bins with 20.3-mm perforated polyethylene liners. Three bins with packed ‘Comice’ fruit were loaded into each of six gas-tight CA cabinets within 10 d after harvest and cooled to temperature of /1 8C. Each cabinet was then sealed and flushed with N2 until the O2 concentration in each cabinet was reduced to the desired level. The CA regime of each cabinet was established within 5 d after sealing. The concentrations of O2 and CO2 established for each cabinet were as follows: Cabinets l/3 1.0% O2/0.031% CO2 (lime) Cabinets 4 /6 2.0% O2/1.0% CO2 After 3 months of CA storage, ‘Comice’ fruits were returned to air storage at /1 8C. In this experiment, each cabinet in each CA treatment was considered as a replicate. Therefore, each CA treatment had three replicates. After holding in air at /1 8C for 1, 2 and 3 months, one bin of fruit from each cabinet of each CA regime was transferred to a ripening room at 20 8C. At the beginning of each sampling interval (i.e. on day 0 of ripening at 208), 5 fruit per replicate were weighed and transferred into a respiration chamber supplied with constant airflow at the rate of 200 ml min 1. The rate of ethylene production from each replicated fruit sample was determined daily for 15 d by a gas chromatograph (Chen and Mellenthin, 1981). On day 1, 3, 5 and 7 of ripening, 10 fruit (designated as an experimental unit) from each of three replicated bins were used for determination of FF, EJ, SSC and TA by the
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285
Table 1 Activity of PDC and ADH, concentration of FAR and CT and incidence of FB and SCALD of ‘Comice’ pears after air storage at /1 8C Storage month
PDC mmol kg min
ADH 1
mmol kg min
FAR 1
mmol m
CT 2
mmol m
1 2 3 4 5 6
0.28 0.44 0.28 0.42 0.33 0.45
0.28 0.24 0.19 0.28 0.33 0.30
29 49 65 78 89 87
1 7 14 21 30 53
LSD.05 Source DFa Storage interval 5
/ Significance NS
/
14
6
NS
**
***
Incidence (%) 2
FB
SCALD
0 0 0 5.49/2.7 36.59/3.3 54.19/4.8
0 0 0 2.69/1.2 26.99/2.4 41.49/4.6
Protein extraction for PDC and ADH activity assay was performed at the beginning of each sampling interval. FAR, CT, FB and SCALD were assessed on day 5 of ripening at 20 8C after each storage interval. NS, **, ***not significant, significant at P /0.01, or at P /0.001, respectively. a DF, Degree of freedom.
methods as described in Section 2.1. On day 5 of ripening, dessert quality of ripened fruit including flesh texture and flavor (acid/sugar balance and aroma) was rated on a nine-point hedonic scale as described in Section 2.2. In addition, incidence (percentage of affected fruits) of storage disorders including IB and SCALD was assessed on day 5 of ripening. A three-way split-plot ANOVA was used for statistical analysis to determine the effect of CA regimes and monthly holding on ethylene production and fruit softening during ripening. In this case, different CA regimes were considered as the main plot, monthly holding as the sub-plot, and days of ripening as the sub-sub-plot. For ethylene production, smooth curves were employed and means among data points were separated by the LSD0.05 while the natural logarithmic function was the best fit for each monthly fruit-softening curve. Other data including EJ, TA and SSC were also subjected to a three-way split-plot ANOVA where different CA regimes were considered as the main plot, monthly holding as the sub-plot, and the state of ripeness as the sub-sub-plot. Means among each measurement were separated by the LSD0.05.
3. Results and discussion 3.1. Storage disorder and ripening behavior of ‘Comice’ pears after air storage Air-stored‘Comice’ fruit developed minor incidents of FB and SCALD disorders after 4 months of storage (Table 1). The symptom of FB includes softening and browning of cortex and core tissues, usually moist with offensive flavor. The symptom of FB does not resemble the symptom of senescent breakdown of apple fruit described by Porritt et al. (1982). They described senescent breakdown as ‘softening and browning of affected areas of cortex tissue, usually dry and poorly defined.’ Incidents of FB and SCALD increased to over 25% that were considered as commercially unacceptable after 5 and 6 months of storage (Table 1). Activity of PDC and ADH in air-stored fruits changed very little throughout 6 months of storage and were not associated with the development of FB disorder. Both FAR and CT concentrations in the peel tissue increased constantly during 6 months of storage with a second degree of polynomial equation as the best fit (FAR / /0.002 /
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Table 2 EJ, (ml kg 1), TA, (mmol l 1), SSC, (%) and dessert quality ratings (score 1-9) of ‘Comice’ pears after 6 monthly storage intervals in air at /1 8C Storage (months)
EJ
TA
SSC
Quality ratings
Unripe
Ripe
Unripe
Ripe
Unripe
Ripe
Texture
Flavor
1 2 3 4 5 6
698 718 712 695 695 687
473 487 570 660 674 671
26.7 24.6 21.2 18.5 19.5 16.8
25.9 20.7 20.0 18.3 19.8 16.9
13.8 14.1 14.1 13.9 13.9 13.7
14.1 14.5 14.5 13.8 13.2 13.6
8.19/0.6 8.39/0.5 8.39/0.6 5.79/0.6 4.39/0.6 3.19/0.7
4.29/0.4 7.19/0.5 8.49/0.5 5.39/0.3 3.79/0.3 3.69/0.4
LSD.05 Source (DF)a S(5) R (1) S /R (5)
34 Significance * ** **
4.l
0.4
** NS NS
NS NS NS
Unripe and ripe fruit refer to the fruit that had been transferred to a ripening room at 20 8C for 1 day or 5 days, respectively. Dessert qualities were assessed on day 5 at 20 8C. NS, not significant; * significant at P /0.05; ** significant at P /0.01. a S, Storage interval; R, ripe or unripe fruit; DF, degree of freedom.
(DS)2/0.801 /(DS)/6.710 (r2 /0.9854); CT / 0.0006 /(DS)2/0.134 /(DS)/2.986 (r2 / 0.9788); where DS represents days in storage and r2 is the correlation coefficient of determination). Therefore, changes in FAR and CT were associated with the development of SCALD disorder (Table 1). Oxidation of a FAR to CT was found to he the cause of superficial scald disorder of ‘d’Anjou’ pears (Chen et al., 1990). The magnitudes of FAR and CT in ‘Comice’ pears, however, were about 5 and 6 times, respectively, less than those in ‘d’Anjou’ pears at each corresponding storage interval (Chen et al., 1990). These data indicated that the biochemical basis of SCALD disorder of ‘Comice’ pears must be somewhat similar to that of superficial scald disorder of ‘d’Anjou’ pears. EJ of fruit stored between 1 and 3 months declined significantly from about 700 ml kg 1 to less than 570 ml kg 1 upon ripening while EJ of fruit stored for 4 months of longer clanged very little (Table 2). The reduction of EJ in ripened fruit was directly associated with the high texture quality, which was scored /8.0 (Table 2). Reduction of EJ is due to an increase in water-soluble pectin in the ripened flesh tissue, which increases the hygroscopic binding capacity (Chen and Bor-
gic, 1985). Ripened flesh tissue with EJ of B/600 ml kg 1 would have a very juicy texture. Although fruit stored for 1 month could ripen with the high texture quality, the flavor quality was scored as low as 4.2 (Table 2). Flavor quality of ripened fruit improved to the highest score after 3 months of storage and then decreased quickly after 4 months of storage or longer (Table 2). The results imply that the increase in aroma flavor in ‘Comice’ pears require a longer period of storage as compared to the development of juicy texture upon ripening. A prolonged storage period ( /4 months) caused ‘Comice’ pears to develop undesirable off flavor upon ripening. TA of fruit decreased consistently during 6 months of storage but there were no significant differences in TA between unripe and ripe fruit (Table 2). Malic acid, the main organic acid found in pear fruit, might have been used as the carbon source in the tricarboxylic acid cycle as part of the respiratory process, resulting in a decrease in TA concentration in winter pear cultivars during storage (Chen et al., 1982). SSC in fruit remained between 13.2 and 14.5% regardless of storage time and state of ripeness (Table 2). Changes in ethylene production and fruit softening during ripening at 20 8C were found to be
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287
Fig. 1. Ethylene production (EP) of ‘Doyenne du Comice’ pears on transfer to 20 8C after removal from refrigerated storage in air at /1 8C for 0, 1, 2, 3, 4, 5 and 6 months.
the best objective measurements of storage life of ‘Comice’ fruit. When ‘Comice’ pears were held at 20 8C for 15 or 7 d after each monthly storage interval at /1 8C, they exhibited different patterns of ethylene production and fruit softening, respectively (Figs. 1 and 2). ‘Comice’ fruit could not produce any measurable amount of ethylene to induce normal ripening without exposure to chilling at /1 8C, as expected of winter pears (Leblond and Ularich, 1973; Drouet and Hartmann, 1979; Blankenship and Richardson, 1985; Morin et al., 1985; Knee, 1987). The amount of chilling required is influenced by storage temperature (Sfakiotakis and Dilley, 1974; Gerasopoulos and Richardson, 1995). As chilling duration increased at /1 8C, the magnitude of ethylene production increased on day 1 of ripening at 20 8C and the number of days required to reach the climacteric-like peak of ethylene production was reduced (Fig. 1). Ethylene production of fruit stored for 4 months or longer progressively decreased without showing the distinctive climacteric-like peak during 15 d of ripening at 20 8C (Fig. 1). Similar ethylene production patterns were reported in ‘d’Anjou’ pears (Chen et al., 1983; Gerasopoulos and Richardson, 1997) and ‘Bose’
pears (Chen et al., 1995). Elgar et al. (1997) reported that ethylene production of ‘Comice’ pears increased with longer storage when initially transferred to higher temperature (i.e. day 1 at 20 8C), but tended to decline during ripening. However, their measurements of ethylene production in the ripening environment at 20 8C were only between day 1 and 7 upon removal from cold storage so that their data could not demonstrate the ethylene climacteric-like peak which occurred on day 8 or 9 of ripening. Nevertheless, our ethylene production data in the 7-day ripening period agreed with those reported by Elgar et al. (1997). In correspondence to ethylene production, ‘Comice’ pears were incapable of softening normally at 20 8C immediately after harvest indicating that a period of chilling was required for the induction of normal ripening capacity (data not presented). Fruit stored in air between 1 and 3 months softened swiftly to FF of 10 N on day 5 at 20 8C (Fig. 2). The optimum ripeness of ‘Comice’ pears for immediate eating was at FF between 10 and 20 N that occurred on day 5 of ripening at 20 8C. The ethylene climacteric peak that occurred on day 8 or 9 of ripening did not synchronize with
288
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Fig. 2. FF of ‘Doyenne du Comice’ pears on transfer to 20 8C after removal from refrigerated storage in air at /1 8C for 1, 2,3, 4, 5, 6 months. The (LSD.05) was 5.6 N. The regression equations are: (1 Mo) y / /21.9 ln(x )/49.9 r2 /0.970; (2 Mo) y / /21.7 ln(x )/ 47.3 r2 /0.975; (3 Mo) y / /22.7 ln(x )/45.3 r2 /0.983; (4 Mo) y / /8.8 ln(x )/37.6 r2 /0.824; (5 Mo) y / /6.4 ln(x )/36.6 r2 / 0.715; (6 Mo) y / /2.3 ln(x )/33.5 r2 /0.702.
the fruit-softening pattern (Figs. 1 and 2), a phenomenon similar to the ripening behavior of ‘d’Anjou’ pears (Chen et al., 1983). Fruit stored in air for 4 months or longer did not soften properly during ripening and remained firmer than 20 (N) on day 7 of ripening (Fig. 2). Based on the development of storage disorders and dessert qualities of ripened fruit combined with the profiles of ethylene production and fruitsoftening, the estimated storage life for ‘Comice’ fruit grown in Hood River Valley would be between 3 and 4 months when stored in air at / 1 8C. Elgar et al. (1997) reported that ‘Comice’ pears grown in New Zealand could develop optimum quality upon ripening when stored in air at /1 8C between 8 and 20 weeks after harvest. The storage life of ‘Comice’ pears grown in Germany was approximately 5 months when stored in air at 0 /0.5 8C and 95% RH (Gram and Ruck, 1985). Our study indicated that storage life of ‘Comice’ pears grown in Hood River Valley, OR was about 1 month less than those grown in New Zealand and Germany.
3.2. Effect of different CA regimes and storage time on storage disorder of ‘Comice’ pears Regardless of different CA regimes and the storage time, ‘Comice’ pears did not develop SCALD. CA-stored fruit maintained the original green skin color similar to the skin condition at harvest (personal observation). Fruit stored in different CA regimes for 3 months were also free from IB after 1 month of holding in refrigerated air plus 5 d of ripening at 20 8C (Table 3). Fruit stored in 0.5 and 1.0% oxygen CA started showing minor incidence of IB after 4 months of storage (Table 3). The symptom of IB includes the diffusive browning discoloration around the cortex tissue and the vascular bundles, usually dry and poorly defined. Occasionally, the core tissue is also affected. The symptom of IB induced by CA is distinctively different from the symptom of FB, which occurred in prolonged air storage. Incidence of IB increased to more than 11.3% when fruit were stored in different CA regimes for 5 month or longer, and was closely associated with oxygen
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289
Table 3 Incidence of SCALD and IB of ‘Comice’ pears following storage in different CA storages and 1 month in air at /l 8C plus 5 days at 20 8C Storage intervals
Type of disorder
0.5% O2 B/0.1% CO2
l.0% O2 B/0.1% CO2
1.5% O2 0.5% CO2
2.0% O2 1.0% CO2
3 months
SCALD IB
0% 0%
0% 0%
0% 0%
0% 0%
4 months
SCALD IB
0% 5.69/1.2%
0% 5.99/1.0%
0% 0%
0% 0%
5 months
SCALD IB
0% 29.89/9.7%
0% 20.79/7.3%
0% 15.69/3.2%
0% 11.39/3.0%
6 months
SCALD IB
0% 81.49/13.2%
0% 46.99/12.6%
0% 25.79/7.3%
0% 17.69/4.2%
concentration rather than carbon dioxide concentration in CA storage. Fruit stored in CA with lower oxygen concentration suffered higher incidence of IB (Table 3). After 3 months of storage, activity of PDC was 0.63, 0.74, 0.63 and 0.56 (mmol kg 1 min 1) in the pulp tissue of fruit stored in 0.5, 1.0, 1.5 and 2.0% O2, respectively while activity of ADH remained between 0.21 and 0.33 (mmol kg 1 min 1) regardless of CA regimes (Table 4). Activity of PDC in fruit increased
significantly between 4 and 6 months of storage, the lower the O2 concentration the higher the PDC activity (Table 4). Regardless of different CA regimes and the storage time, ADH activity changed very little (Table 4). Thus, development of IB might be induced by the increased PDC activity that resulted in the accumulation of acetaldehyde inside the pulp tissues. Our results suggested that PDC activity in ‘Comice’ pears was induced by the combination of low oxygen level
Table 4 Activity of PDC and ADH in ‘Comice’ pears following storage in different CA storages at /1 8 and 1 month in air plus 1 day at 20 8C Storage intervals
Activity (mmol kg 1 min 1)
0.5%O2 B/0.1% CO2
1.0% O2 B/0.1% 1.5%O2 0.5% CO2 CO2
2.0% O2 1.0% CO2
3 months
PDC ADH PDC ADH PDC ADH PDC ADH
0.63 0.21 0.84 0.26 1.94 0.30 2.15 0.32
0.74 0.27 0.87 0.22 l.72 0.28 1.94 0.25
0.56 0.30 0.62 0.31 0.83 0.33 1.71 0.32
4 months 5 months 6 months LSD.05 /0.14 (mmol kg 1 min 1) (PDC)
Significance a
Source (DF) S(3) CA (3) S /CA (9)
PDC ** * **
ADH NS NS NS
NS, not significant; * significant at P /0.05; ** significant at P /0.01. a S, storage interval; CA, CA regimes; DF, degree of freedom.
0.63 0.33 0.64 0.29 0.81 0.26 l.69 0.30
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Table 5 EJ, (ml kg 1), TA, (mmol l 1), SSC, (%) and dessert quality ratings (score 1 /9) of ‘Comice’ pears after 3 months of CA storage followed by l, 2 or 3 months in air at /l 8C CA regime
1% O2; B/0.03%CO2
2% O2; l% CO2
LSD.05 Source (DF)a CA (1) HD (2) R(1) CA /HD (2) Ca /R (1) HD /R (2) CA /HD /R
Holding (months)
1 2 3 1 2 3
EJ
TA
SSC
Quality ratings
Unripe
Ripe
Unripe
Ripe
Unripe
Ripe
Texture
Flavor
705 710 715 713 695 707
505 517 515 515 506 641
22.8 21.6 19.2 19.9 19.5 17.2
21.5 20.5 19.7 19.8 19.0 16.9
14.2 14.0 13.8 14.3 13.9 13.9
13.9 14.3 14.2 14.1 13.9 13.4
8.39/0.4 8.l9/0.7 7.89/0.5 7.79/0.6 8.39/0.5 5.19/4.4
7.29/0.5 8.19/0.3 7.79/0.6 7.39/0.4 7.79/0.6 6.69/0.7
34 Significance * * ** ** ** ** **
4.1 NS ** NS * NS NS NS
NS NS NS NS NS NS NS
Unripe and ripe fruit referred to fruit that had been transferred to a ripening room at 20 8C for 1 day or 5 days, respectively. Dessert qualities were assessed on day 5 at 20 8C. NS, not significant; * significant at P /0.05; ** significant at P /0.01. a CA, CA regimes; HD, holding period (months); R, ripening state; DF, degree of freedom.
and time of CA storage. Nanos et al. (1992) have suggested that removal of acetaldehyde is physiologically important, for the compound has long been known as a cause of physiological disorders in pears (Harley, 1927, 1929). It has been reported that acetaldehyde is more toxic than ethanol (Perata and Alpi, 1991). Roelofts and Van Hermon (1994) reported that ‘Doyenne du Comice’ pears stored at /0.5 8C in 2% oxygen with 0.2, 1.0 or 2.0% carbon dioxide maintained similar FF after 4 and 5 months while incidence of FB increased from nil up to an average of 9% after approximately 5 months of storage and 30% after approximately 6 months of storage. Their data indicated that incidence of FB was lowest in the lower carbon dioxide concentration and brown core disorder occurred with all CA storages even after approximately 4 months of storage and increased rapidly during post-storage ripening at room temperature. They did not define the symptoms of ‘FB’ disorder which presumably were similar to symptoms of ‘IB’ disorder described here.
3.3. Ripening behavior and storage disorder of ‘Comice’ pears after short-term CA storage ‘Comice’ pears stored either in 1.0% O2/ B/ 0.1% CO2 or in 2.0% O2/0.8% CO2 CA for 3 months were free from any storage disorders when the CA-stored fruit were held in air at /1 8C for 3 months plus 5 d of ripening at 20 8C (data not presented). Regardless of CA regime and holding period, there was a reduction of EJ when fruit were ripened (Table 5). Fruit stored in 1% O2 contained higher TA than those in 2% O2 but there was no difference in TA between unripe and ripe fruit (Table 5). SSC was not affected by treatment (Table 5). Both texture and flavor of ripe fruit scored above 7 on a nine-point hedonic scale except that overall dessert quality of 2% O2-stored fruit scored lower after 3 months of holding in refrigerated air (Table 5). Regardless of CA regime, patterns of ethylene production and fruit softening of CA-stored fruit resembled those of air-stored fruit that had been stored for 1 /3 months (Figs. 3 and 4). The results demonstrated
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291
Fig. 3. Ethylene production of ‘Comice’ pears during 15 days at 20 8C after 3 months of CA storage plus monthly holding intervals in refrigerated air (RA) at /1 8C.
that a short-term (i.e. 3 months) CA storage of ‘Comice’ pears extended the normal ripening capacity and maintained high dessert quality even after CA-stored fruit had been returned to refrigerated air storage for as long as 3 more months. Bertolini and Casadei (2000) also reported that low-O2 storage (1.5% O2/0.8% CO2) of Conference and Doyenne du Comice pears produced higher acidity, greener coloring and faster flesh softening during shelf-life than standard CA storage (3% O2/3% CO2). Garcia and
Streif (1993) assessed six pear cultivars for their suitability for CA storage using 3% O2/ B/1% CO2; 3% O2/3% CO2; 1% O2/ B/1% CO2; and 1% O2/3% CO2 at /1 8C. They concluded that Packham’s Triumph appeared to be the most suitable for CA storage, followed by Conference and Comice. They also indicated that both ‘Comice’ and ‘Packhams’ tolerated up to 3% CO2 while ultra-low O2 (ULO) concentration (1%) improved the keeping quality of these two cultivars.
292
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Fig. 4. FF of ‘Comice’ pears during 7 days at 20 8C after 3 months of CA storage plus monthly holding in refrigerated air (RA) at /1 8C.
In addition to the CA regimes discussed above, there have been other reports on the optimal CA regime for extending storage life of ‘Comice’ pears grown in different countries. Optimum CA regime for storage of pear cultivars including ‘Doyenne du Comice’ grown in Russia was found to be 8% O2 and 5% CO2 at 2 /3 8C (Shcherbatko and Korzhov, 1985). Recommended CA regime for storage of ‘Doyenne du Comice’ grown in France
was 5% O2 and 5% CO2 at 0 8C that could extend the storage life for 6 months (Leblond, 1986). In the present study, a CA regime with O2 level of 2% or lower could induce undesirable ‘IB’ disorder if ‘Comice’ pears were stored under these CA environments for longer than 3 months. It is evident that certain unknown environmental factors during fruit growth and maturation influence the optimum CA regime for extending storage life
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and avoiding storage disorders of ‘Comice’ pears grown in different regions.
4. Summary ‘Doyenne du Comice’ pears (Pyrus communis , L.) harvested at commercial maturity with FF of 55.1 N (9/2.8 N) from mature trees grown in the Hood River Valley, OR, ripened normally after 30 d of chilling at /10 8C. The storage life of ‘Comice’ pears in air at /1 8C was estimated about 4 month or shorter as judged by the criteria that the stored fruit remained free from any storage disorders, demonstrated a climacteric-like peak of ethylene production and were capable of softening properly with desirable dessert quality at 20 8C. Short-term (3 months) CA storage with 1% O2/ B/0.1% CO2 or 2% O2/1% CO2 could prevent ‘Comice’ pears from developing storage disorder and preserve the normal ripening behavior after they had been returned to air storage at /1 8C for as long as 3 months. This study provides the pear industry with useful information for marketing air-stored ‘Comice’ pears during the first 3 months after the fruit have satisfied the chilling requirement (:/1 month in air at /1 8C) followed by marketing short-term (3 months) CAstored fruit for another 3 months during the rest of marketing season.
Acknowledgements Oregon State Agricultural Experimental Station Technical Paper No. 11875. This study was supported by the Winter Pear Control Committee, USA.
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