March 1, 2000

Response of d'Anjou pears to controlled atmosphere storage in elevated temperature and carbon dioxide

By S.R. Drake, USDA-ARS-TFRL, Wenatchee, Washington, and R.D. Gix, Blue Star Growers, Inc., Cashmere, Washington

Ninety-six boxes of commercially packed, controlled atmosphere (CA) storage quality d'Anjou pears were obtained from four warehouses with two grower lots per warehouse. Immediately after packing, the pears were divided into groups of 24 each and placed in four commercial CA storage environments (31°F at either 1% or 3% CO₂, or 34°F at either 1% or 3% CO₂). The pears were stored in CA for 90, 150, or 210 days, plus 30 days of regular atmosphere storage to simulate shipping and handling. D'Anjou pears stored at 31°F were firmer and greener with less decay than pears held at 34°F. Pears stored in 3% CO₂ were firmer and greener with enhanced appearance and finish, and reduced amounts of scald and decay than pears held in 1% CO₂. Pears stored at 31°F in 3% CO₂ produced superior quality pears when compared to pears stored in 1% CO₂.

INTRODUCTION

Atmospheres of 1% to 2% O₂ and <1% CO₂ are recommended for controlled atmosphere (CA) storage of d'Anjou pears (Hansen and Mellenthin, 1979; Hardenburg et al., 1986). Using 2% or less O₂ for long-term storage reduced loss of firmness, acidity, greenness, and scald severity (Chen et al., 1981; Mellenthin et al., 1980; Richardson and Meheriuk, 1989). Elevated levels of CO₂ (up to 3%) have been assessed under laboratory conditions (Allen and Claypool, 1948; Drake, 1994; Hansen, 1957), but the results have been controversial.

Standard oxygen and carbon dioxide levels for CA storage of d'Anjou pears in the Wenatchee, Washington, growing area are 1.5% to 2% O₂ and <1% CO₂ at 31°F, which is a common procedure (Meheriuk, 1993). To maintain CO₂ at levels at <1% and temperatures of <34°F is costly and time-consuming to the storage facility. The CA storage law in Washington State requires that winter pears must be stored at 5% O₂, for a minimum of 60 days before the pears can be certified as CA storaged (Washington Agriculture Code, 16-449-010). No CO₂ or storage temperature is specified in this state requirement. This research was conducted to determine the quality of d'Anjou pears stored under commercial conditions at higher than normal CO₂and temperature levels.

MATERIALS AND METHODS

Four commercial pear storage warehouses provided 24 packed boxes (12 boxes from each of 2 growers) of CA quality pears, size 80. One to two days after packing, the pears were collected from each warehouse and transported to the commercial research facility located at Stemilt Growers, Inc., Wenatchee, Washington. Boxes of pears from each warehouse were randomly divided into four CA treatments (using warehouses as replication) and placed under four different storage regimes (1.5% O₂ and <1% CO₂, or 1.5% O₂ and 3% CO₂ at either 31°F, or 34°F). All storage treatments were, or have been, used by the various warehouses in Washington State. The atmosphere in each room was established and maintained using a purge-type computer-controlled CA system. A Servomix analyzer, model 1400B4, was used to determine atmosphere (O₂ and CO₂) concentration on a daily basis. Each room has the capacity for 40 bins of fruit; CA quality filler pears were used to fill each room to capacity. After 90, 150, and 210 days of CA storage, one box of pears from each grower and warehouse was removed. Immediately after each storage period, one-half of the pears in a box were removed and quality evaluated on 20 pears immediately and on 20 pears after an additional seven days at 68°F. The remaining one-half boxes were held in regular atmosphere (RA) storage at 34°F for an additional 30 days to simulate shipping and handling time. Quality evaluations were made on 20 pears after removal from RA and on 20 pears after an additional seven days at 68°F. Quality factors evaluated were firmness, external and internal color, soluble solids concentration (SSC), titratable acidity (TA), finish, and visual disorders (scald, shrivel, stem condition, dark skin disorder, and pithy brown core). After 210 days of CA and three days at 68°F, one tray of 20 pears (10 from each grower lot) from each warehouse and storage treatment were evaluated for finish, scald, shrivel, dark skin disorder, and stem condition. Sensory evaluations (visual disorders) were made by 20 individuals skilled in quality control, who were selected from all of the participating warehouses and were asked to evaluate the pears on a scale of 1 = none/excellent, 2 = slight/good, 3 = moderate/fair, and 4 = severe/poor.

Firmness, in pounds was determined using the TA-XT2 Texture Analyzer (Texture Technologies, Scarsdale, NY) equipped with a 7.7-mm probe. External and internal color was determined with The Color Machine (Pacific Scientific, Silver Springs, MD) using the Hunter L*, a*, b* system and calculated hue values (Hunter and Harold, 1987). SSC and TA were determined from a composite of juice expressed from longitudinal slices from each of 10 fruit.

An Abbe-type refractometer with a sucrose scale calibrated at 68°F was used to determine SSC. TA was measured with a Radiometer titrator, model TTT85 (Radiometer, Copenhagen, Sweden). Acids were titrated to pH 8.2 with 0.1N NaOH and expressed as percent malic acid. Visual disorders (scald, shrivel, dark skin disorder, and stem condition) of laboratory samples were determined by two individuals familiar with winter pear disorders and rated on a scale of 1 to 4 (1=none; 4=severe). Data were analyzed using MSTAT-C (1988) as a factorial design using storage treatments as the main plot and storage time and ripening as the subplots. Based on significant F tests, means were separated using Duncan's multiple range test (DMRT).

RESULTS AND DISCUSSION

Firmness retention measured immediately after storage was best in pears that had been held at either 31°F, or 34°F in a 3% CO₂ atmosphere (see Table 1). Storage of d'Anjou pears at 34°F reduced firmness, but only when held in a 1% CO₂ atmosphere. If the storage atmosphere was maintained in 3% CO₂, the pears were firmer than when held at 31°F in 1% CO₂ (12.8 compared to 11.9 lbs.). After seven days of ripening, all pears had a firmness of less than three pounds regardless of storage temperature or atmosphere, but the pears held at 31°F in 3% CO₂ were firmer than those stored at 31°F, or 34°F in 1% CO₂.

Immediately after removal from storage, only those pears held at 34°F at 1% CO₂ displayed scald (1.2%). Pears in all other storage temperatures and atmospheres displayed less than 1% scald (see Table 1). After seven days of ripening, some scald was present regardless of temperature or atmosphere, but was less if the pears were held in 3% CO₂ versus 1% CO₂ at either 31°F or 34°F. In addition, pears stored at 34°F developed more scald than pears stored at 31°F.

D'Anjou pears held at 34°F in 1% CO₂were lighter in color (higher L values) and less green (higher a values) and more yellow (lower hue values) immediately after storage and after seven days of ripening than pears from all other storage temperatures and atmospheres. Pears held in 3% CO₂ were greener with less yellow than pears held in 1% CO₂ immediately after storage and after seven days of ripening regardless of storage temperature. A darker color (lower L values) was more evident in pears held at 31°F than in pears held at 34°F. There is no doubt that lower temperatures and higher CO₂ in the storage environment retards the change in color from a green to a more yellow pear.

Decay of d'Anjou pears was influenced by not only storage temperature, but also by storage atmosphere (see Table 2). Pears stored at 31°F had very little decay regardless of the amount of CO₂ in the storage atmosphere. Decay incidence was higher in pears stored at 34°F in 1% CO₂ compared to pears at 34°F in 3% CO₂, or pears stored at 31°F regardless of the amount of CO₂ present. In this particular study, the use of CO₂ at higher than normal levels (3%) reduced the amount of decay present in d'Anjou pears, and this agrees with previous laboratory studies (Allen and Claypool, 1948; Drake, 1994; Hansen, 1957) conducted under laboratory conditions. This study was conducted under commercial conditions, and the results are similar to other studies conducted under laboratory conditions.

Pithy brown core in d'Anjou pears has long been related to elevated CO₂ in the storage atmosphere, and to eliminate this problem, the use of less than 1% CO₂ in the storage atmosphere has been recommended (Meheriuk, 1989). In this study, pithy brown core was not related to either storage temperature or the amount of CO₂ in the storage atmosphere (see Table 2). A higher percentage of d'Anjou pears stored at 3% CO₂ displayed no pithy brown core compared to pears stored at 1% CO₂. Pears stored in 1% CO₂ displayed a higher percentage of slight pithy brown core than pears stored in 3% CO₂, particularly when stored at 31°F. Regardless of storage temperature or storage atmosphere, all of the pears in this study displayed less than 1% pithy brown core.

After 210 days of storage, quality control personnel determined that storage temperature and atmosphere had a significant influence on d'Anjou pear quality (see Table 3). Pears stored at 31°F in 3% CO₂ had a superior appearance, less scald, and a better stem condition than pears stored at 31°F in 1% CO₂, or pears stored at 34°F in either 1 or 3% CO₂. Finish tended to be superior in pears stored at 31°F in 3% CO₂. Dark skin disorder, speckled skin, and shrivel were not influenced by either storage temperature or storage atmosphere.

CONCLUSIONS

D'Anjou pears stored at 31°F are firmer and greener with less decay than pears held at 34°F. Pears stored in 3% CO₂ are firmer and greener with enhanced appearance and finish, and reduced amounts of scald and decay than pears held in 1% CO₂. Pears stored at 31°F in 3% CO₂ produce superior quality pears when compared to pears stored in 1% CO₂.

If the storage temperature cannot be maintained and pears are stored at a higher temperature (34°F), the use of 3% CO₂ would aid in quality retention. Energy savings have been documented in storage systems using elevated CO₂ levels when compared to standard CO₂ levels (Wealti and Cavaliere, 1990). Use of 3% CO₂ in this study enhanced d'Anjou pear quality without loss from disorders or decay.

Results of this study, conducted under commercial conditions, are in accord with previous laboratory studies.

REFERENCES

Allen, F.W. and L.L. Claypool, "Modified atmosphere in relation to the storage life of Bartlett pears," Proc. Amer. Soc. Hort. Sci. 59 (1948):192-204.

Chen, P.M., R.A. Spotts, and W.M. Mellenthin, "Stem-end decay and quality of low oxygen stored d'Anjou pears," J. Amer. Soc. Hort. Sci. 106 (1981):522-527.

Drake, S.R., "Elevated carbon dioxide storage of d'Anjou pears using purge-controlled atmosphere," HortSci. 29 (1994):299-301.

Hansen, E., "Reactions of d'Anjou pears to carbon dioxide and oxygen content of the storage atmosphere," Proc. Amer. Soc. Hort. Sci. 69 (1957):110-115.

Hansen, E. and W.M. Mellenthin, "Commercial handling and storage practices for winter pears," Oregon State Univ. Agr. Expt. Sta. Rpt. 550, 1979.

Hardenburg, R.E., A.E. Watada, and C.Y. Wang, "The commercial storage of fruits, vegetables, and florist and nursery stocks," U.S. Dept. of Agr., Agr. Hdbk. 66, 1986.

Hunter, R.S. and Harold, "The measurement of appearance," 2nd ed. Wiley, New York, 1987.

Meheriuk, M., "CA storage conditions for apples, pears and nashi," vol 2. In: Proc. 6th. Intl. Controlled Atmosphere Res. Conf., p. 819-858, June 1993, Ithaca, NY.

Mellenthin, W.M., P.M. Chen, and S.B. Kelly, "Low oxygen effects on dessert quality, scald prevention, and nitrogen metabolism of d'Anjou pear fruit during long-term storage," J. Amer. Soc. Hort. Sci. 105 (1980):695-698.

MSTAT-C, Version 1.0. Michigan State Univ., East Lansing, 1988.

Richardson, D.G. and M. Meheriuk, "CA recommendations for pears (including Asian pears)," vol 2. In: J.K. Fellman (ed.). Proc. 5th Intl. Controlled Atmosphere Res. Conf., p. 285-302, June 1989, Wenatchee, WA.

Washington Agriculture Code 16-449-010, "Washington controlled atmosphere storage requirements for winter pears," September 20, 1973. Washington Dept. of Agriculture, Olympia, WA.

Wealti, H. and R.P. Cavalieri, "Matching nitrogen equipment to your needs," Tree Fruit Postharvest J. 1 (1990):3-13.

The authors would like to express appreciation to the Washington Tree Fruit Research Commission for partially funding this study and to the cooperating packing facilities (Blue Bird, Blue Star, Cashmere Fruit Exchange, Independent, Peshastin Hi-Up, and Stemilt).

T A B L E 1

Quality attributes of d'Anjou pears as influenced by storage temperature and storage atmosphere.

Storage Storage Ripe Firmness Scald Hunter color

temperature atmosphere (days) (lbs) (%) L* a* hue

31°F 1.5% O₂ and 1% CO₂ 0 11.9b^Z <1.0d 65.3g -5.5e 101.4b

7 2.3ef 2.3b 70.9c -1.4b 92.6e

1.5% O₂ and 3% CO₂ 0 13.2a <1.0d 64.2h -6.2f 103.0a

7 2.8d 1.3c 69.7d -2.6c 94.9d

34°F 1.5% O₂ and 1% CO₂ 0 11.2c 1.2c 68.4e -4.1d 98.6c

7 2.1f 3.4a 74.1a 0.2a 89.8f

1.5% O₂ and 3% CO₂ 0 12.8a <1.0d 66.2f -5.9f 103.1a

7 2.6de 1.6c 72.1b -1.6b 93.0e

Means in a column not followed by a common letter are significantly different by DMRT (P ¾ 0.05).

T A B L E 2

Disorders (decay and pithy brown core) of d'Anjou pears, after storage, evaluated by laboratory personnel.

Storage Storage Decay^z Pithy brown core (% affected)^y

temperature atmosphere (%) None Slight Scorable

31°F 1.5% O₂ and 1% CO₂ <1.0b 80.6b 19.4a <1.0a

1.5% O₂ and 3% CO₂ <1.0b 82.1a 17.9b <1.0a

34°F 1.5% O₂ and 1% CO₂ 1.3a 81.4ab 18.6ab <1.0a

1.5% O₂ and 3% CO₂ <1.0b 82.4a 17.6b <1.0a

^ZEvaluated on a scale of 1 to 4 (1 = excellent, 2 = good, 3 = fair, 4 = poor).

^YMeans in a column not followed by a common letter are significantly different by DMRT (P ¾ 0.05).

T A B L E 3

Subjective evaluation of d'Anjou pears by 25 warehouse quality control personnel after 210 days of controlled atmosphere storage.

Storage Storage Dark skin Speckled Stem

temperature atmosphere Appearance^Z Finish^Z disorder^Z skin^Z Shrivel^Z Scald^Z condition^Z

31°F 1.5% O₂ and 1% CO₂ 2.9a 2.5ab 1.6a 1.3a 1.4a 1.4a 2.2a

1.5% O₂ and 3% CO₂ 2.2b 2.1b 1.2a 1.3a 1.3a 1.1b 1.8b

34°F 1.5% O₂ and 1% CO₂ 2.9a 2.6a 1.4a 1.3a 1.3a 1.3ab 2.0ab

1.5% O₂ and 3% CO₂ 2.6ab 2.4ab 1.4a 1.3a 1.2a 1.2ab 1.8b

^ZEvaluated on a scale of 1 to 4 (1 = excellent, 2 = good, 3 = fair, 4 = poor).

Means in a column not followed by a common letter are significantly different by DMRT (P¾0.05).

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