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WSU-TFREC/Postharvest Information Network/Methyl Bromide Fumigation of 'Rainier' Sweet Cherries in Corrugated Polypropylene Containers



Methyl Bromide Fumigation of 'Rainier' Sweet Cherries in Corrugated Polypropylene Containers


Abstract

Since sweet cherries are sensitive to mechanical injury, a postharvest process that reduces handling, such as fruit fumigation in field containers, would conserve product quality. Fumigation of 'Rainier' sweet cherries with methyl bromide in polypropylene plastic inserts placed inside wooden bulk apple bins resulted in concentration-time values similar to those for fumigation in bulk wooden bins and equal to or greater than those recorded during the confirmatory test of efficacy for 'Rainier' cherries. Organic bromide residue levels in 'Rainier' cherries fumigated in the polypropylene plastic inserts declined rapidly from a high of 4.5 ppm to 1 ppb or less within 5 days posttreatment. Inorganic residue levels after treatment were 4.5 to 5.3 ppm and are within the range previously found for other cultivars of cherries.

Introduction

Sweet cherries exported to Japan from the United States must be fumigated with methyl bromide to prevent entry of the codling moth, Cydia pomonella (L.) (Lepidoptera: Tortricidae) (Moffitt et al., 1992). The approved treatment schedules are 64 g/m3 for 2 h at 6 to 12°C, 48 g/m3 for 2 h at 12 to 17°C, 40 g/m3 for 2 h at 17 to 22°C, or 32 g/m3 for 2 h at > 22°C (Moffitt et al., 1992). Approved cherry cultivars are: 'Bing', 'Van', 'Lambert', 'Rainier', 'Garnet', 'Brooks', and 'Tulare.' 'Sweetheart' and 'Lapins' are expected to be approved soon.

Sweet cherries are sensitive to mechanical injury, such as transferring fruits from field containers to other receptacles, and a reduction of fruit handling in the postharvest operation would be beneficial. Japan has approved cherry fumigation in bulk wooden bins and heavy polyethylene plastic lugs. Fumigations in lightweight corrugated plastic containers used in harvest, however, would conserve fruit quality, particularly for the 'Rainier' cultivar. Plastic containers are designed to be used for harvesting, grading, and sorting the fruit in the orchard. These containers could also replace bulk wooden bins and polyethylene pick lugs during fumigation. At the packinghouse, one type of container is designed for the fruit to be transferred to a standard fiberboard carton with plastic liner for shipment to Japan while the other container is designed to be placed entirely within the standard fiberboard carton as an insert within the plastic liner.

This report presents the results of tests of the sorption and desorption of methyl bromide with these different types of corrugated polypropylene containers.


Materials and Methods

Test Containers
Two types of corrugated polypropylene containers were examined. Both are used for picking and sorting the fruits in the field, then for holding the fruit during fumigation. For the first container, the lug, the fruits are transferred after fumigation to the standard fiberboard carton with the plastic liner for shipping. Lug dimensions were 43.2 cm long x 27.9 cm wide x 22.9 cm deep. The lug was slightly larger at the top and tapered to a smaller bottom. Wire handles were on the top of each short side. Each lower corner was perforated with a 1.9 mm diameter opening. Each lug holds ca. 8.2 kg (18 lb) of fruits.

For the second container, the insert is also used during handling and fumigation. The fruits are placed, while still inside the insert, into the standard fiberboard carton for shipping. Dimensions of the insert are 38.1 cm long x 30.5 cm wide x 14 cm deep. The insert was slightly larger at the top and tapered to a smaller bottom. There were no wire handles. On the long sides and on the bottom were numerous 6 mm perforations. On each edge formed by the long sides and the bottom were four 7 mm x 32 mm slots. Each insert holds ca 6.8 kg (15 lb) of fruits.

Test Procedures
Market quality 'Rainier' cherries were supplied by local packing houses and stored at about 2°C until used. For fumigation, nine lugs were placed one layer deep in a standard wooden bulk cherry bin with the following dimensions: 119.4 cm long x 119.4 cm wide x 53.3 cm deep (OD). Three bins were stacked one on top of the other in the chamber for fumigation.

For the inserts, four layers of nine inserts per layer were placed in a standard wooden apple bin with the following dimensions: 119.4 cm long x 119.4 cm wide x 71.1 cm deep (OD). Each layer of inserts was separated from the layer below it by wooden slats placed across the tops of the inserts below. These wooden slats were 115.6 cm long x 0.4 cm wide x 0.2 mm deep. Two bins containing the inserts were stacked in the chamber for fumigation.

Also included in the test was the standard wooden bulk cherry bin without any containers inside. Dimensions for these wooden bulk cherry bins were the same as those used for holding the polypropylene plastic lugs. As with the plastic lugs, three wooden bulk cherry bins were stacked in the chamber for fumigation.

Test Facilities
All fumigations were conducted in a chamber 1.35 m wide, 2.58 m high, and 1.40 m deep. An air circulation system added another 0.03 m3 of volume for a total chamber volume of 4.88 m3. The chamber was equipped with a combination heating-cooling system to maintain the specified temperature. An air circulation system operated continuously throughout the exposure period.

Temperatures during fumigation were monitored using a Campbell data logger equipped with thermocouples. Thermocouples were inserted into individual cherries in the top, middle, and bottom bins; other thermocouples measured air temperature at the top and bottom bins.

Concentrations of methyl bromide were measured using gas chromatography. Temperatures and methyl bromide concentrations were measured after 0, 10, 30, 60, and 120 min exposure for each fumigation. Concentration-Time (CT) products were calculated from methyl bromide concentrations measured during fumigation (Monro, 1969) and expressed in gram hours per cubic meter (gh/m3).

For tests with polypropylene lugs using three wood cherry bins per fumigation, the load factor was 46.7% (load volume: total volume). For the polypropylene insert, using two wooden apple bins, the load factor was 41.6%.

Treatment Procedures
All fumigations were conducted with methyl bromide at 64 g/m3 for 2 hours at 6°C with a 2-hour exposure period and at normal atmospheric pressure. Two fumigations were conducted for each type of container: polypropylene plastic lug, polypropylene plastic insert, or wood bulk bin. Cherries for the residue analyses were treated at the same time as the studies for sorption and desorption of methyl bromide in the different containers as reported above (64 g/m3 for 2 hours at 6°C).

After fumigation, the cherries were held at ~ 2°C in fiberboard cartons with plastic liners. Cherries from the polypropylene plastic lugs were transferred to the fiberboard carton. The entire polypropylene plastic insert was placed inside the polyethylene liner within the fiberboard carton. Samples of cherries for analysis were taken 6 hours, and 1, 2, 3, 5, and 7 days after treatment and then frozen. The frozen samples were sent to the USDA-ARS Horticultural Crops Research Laboratory in Fresno, California, for residue analysis.

Phytotoxicity Tests
After fumigation, the cherries were cooled and transported immediately to the USDA-ARS-TFRL in Wenatchee, WA. Upon arrival, the cherries were placed in cold storage at 1°C and quality evaluated after 7, 14, and 21 days of storage. After each storage period, one-third of the fruit was removed for quality evaluations. Quality evaluations consisted of fruit firmness, soluble solids concentration (SSC), titratable acidity (TA), objective fruit and stem color, and subjective quality determinations for both fruit and stem. Firmness was determined using the Universal TA-XT2 texture analyzer equipped with a 3-mm probe and a penetration distance after contact of 7 mm and the values expressed in Newtons (N). SSC of the cherries was determined with an Abbe-type refractrometer with a sucrose scale calibrated at 20°C. Acids were titrated to pH 8.2 with 0.1 N NaOH and expressed as percentage of malic acid. Objective color of the fruit and stems was determined with The Color Machine using the Hunter L, a, b scale and calculated hue values. Subjective quality of the fruit and stems was determined using two laboratory personnel familiar with cherry grades. Fruit and stems were rated individually on a scale of 1 to 3 (1=best; 3=poorest).

Residue Analysis
In commercial settings, fumigated cherries in inserts would desorb bromide slower than fumigated cherries in lugs because the inserts with fruits would be placed together in packing boxes for shipment rather than removed from lugs and packed separately. Thus, only fumigated cherries from inserts were analyzed for bromide residue. For each sample interval (i.e., 6 hours and 1, 2, 3, 5, and 7 days posttreatment), triplicate 100 g samples of cherries were taken at random from each treatment. The controls were 100 g of untreated cherries. Organic bromide residue analyses were conducted following the headspace method of King et al. (1981) as later modified by Harvey et al. (1989) and Hartsell et al. (1992). Additional triplicate 100 g samples were taken randomly from each replicate for each treatment for inorganic bromide analysis. Inorganic bromide residues were determined using X-ray fluorescence spectrophotometry (Harvey et al., 1989; Hartsell et al., 1992; Hinsch et al., 1992).

Data Analysis
Nonparametric two-sample tests were done by using PROC GLM on ranked data, which is the equivalent to a Wilcoxon rank sum test using the t approximation for significance (SAS Institute, 1982).


Results and Discussion

Sorption
Fruit temperatures were near, but below 6°C during the fumigation of the different containers (Table 1). Based on the greatest percent sorption and lowest CT-values, the inserts had the best methyl bromide penetration (Table 2). These variables were not significantly different between those of inserts and of bulk bins (t = 8.00, df=3, P =ns). Box inserts may facilitate the dispersal of methyl bromide by compartmentalizing the fruit in the bins and allowing the fumigant to move through the insert openings. No statistical differences were found between the lugs and bulk bins for percent sorption and CT-values (t = 0.50, df=3, P =ns, for both comparisons). Use of polypropylene lugs does not interfere with the penetration of methyl bromide during fumigation.

Table 1. Pooled air (from 2 thermocouples) and fruit (from 3 thermocouples) temperatures in different location during fumigation at 65 g/m3 for 2 hours at 6°C on 'Rainier' sweet cherries.
Container
Rep.
Site
No. samples
Ave.
SEM
Lugs
1
Air
10
5.3
0.2
Fruita
10
5.1
0.4
2
Air
10
4.8
0.1
Fruit
15
4.9
0.1
Inserts
1
Air
10
7.2
0.4
Fruit
15
5.7
0.1
2
Air
10
4.7
0.3
Fruit
15
5.9
0.1
Bulk bins
1
Air
10
5.6
0.3
Fruit
15
5.1
0.0
2
Air
10
5.6
0.5
Fruit
15
5.8
0.0
aMalfunctioned thermocouple not used.



Table 2. Percent sorption and CT-values of different containers during methyl bromide fumigation at 64g/m3 for 2 hours at 6°C on 'Rainier' sweet cherries; each container treatment had two replicates.
% sorption
CT-value
Container
Ave.
SEM
Ave.
SEM
Lugs
19.4
4.1
94.9
3.0
Inserts
32.1
3.4
87.6
2.3
Bulk bins
24.8
3.1
91.5
0.7

Phytotoxicity
'Rainier' sweet cherry firmness was directly related to the procedures during methyl bromide fumigation (Table 3). Methyl bromide treated cherries lost firmness when compared to control fruit. In addition, handling procedures had a direct influence on firmness. Cherries fumigated in the lug or bin were less firm than cherries fumigated in the insert with no additional handling. Firmness of the cherries fumigated in the insert (6.3) was less firm than control fruit (6.8), but much firmer than cherries from the other handling procedures (5.0 and 5.3). This difference of at least 1.0 N between fumigation methods would have an impact on the consumer acceptance of the cherries.

Table 3. Quality evaluation of 'Rainier' cherries as influenced by container and cold storage (1°C) time (in days).
Firmness
(N)
SSC
(%)
TA
(% malic)
Visual Fruit color Stem color
Fruit
Stem
L
hue
L
hue
Treatment
Container
Control
6.8a
17.2 0.38b 1.3d 1.5b 61.8a 52.5b 41.0a 98.9a
Lug
5.0d 17.0 0.41a 3.5b 2.4a 53.7c 58.8a 35.7b 83.0b
Insert
6.3b 17.3 0.43a 2.5c 2.1a 59.1a 57.7ab 37.2b 95.5a
Bin
5.3c 17.1 0.42a 3.8a 2.5a 55.7b 58.5a 35.3b 84.6b
Storage time (days)
0
6.3a 17.0c 0.41 2.4b 2.1b 55.6b 54.4b 35.4b 87.2b
7
5.8b
17.3b
0.41
3.0a
1.8c
55.5b
57.8b
38.9a
96.9a
14
5.4c 17.6a 0.40 3.0a 2.5a 61.6c 55.7ab 37.6a 87.4b

Mean separation in a column, with treatments by Duncan's multiple range test (P=0.05).

SSC of sweet cherries was not influenced by methyl bromide fumigation, but fumigation had a strong influence on the TA of the cherries. The TA of cherries was increased by all methyl bromide procedures over the control fruit. This increase in TA was most probably related to moisture loss during fumigation.

Visual assessment of both fruit and stems was greatly influenced by methyl bromide fumigation and fumigation procedure. Regardless of the fumigation procedure used, methyl bromide treated fruit was less acceptable than control fruit. Fruit fumigated in the insert was of higher quality than fruit fumigated in the lug or the bin. Stem quality of methyl bromide treated fruit was similar between procedures, but much reduced when compared to control stems.

Hunter color assessment was similar to the visual assessment of the fruit. The Hunter L and hue values for fruit fumigated in the insert were similar to the L and hue values for control fruit. Hunter L values for fruit fumigated in the lug or bin were less than the control or insert fumigated fruit. This difference in Hunter L values would indicate that fruit fumigated in the lug or bin would be much darker than the control fruit or fruit fumigated in the insert. The darker colored fruit would be much less acceptable by the consumer, particularly when one considers that 'Rainier' cherries have a bright yellow color before being fumigated.

Stem color (Hunter L and hue) was also influenced by fumigation. Regardless of fumigation procedure, Hunter L values for fumigated fruit were much less than the L value for control. This difference in L values would indicate that the fumigate stems were darker in color and less acceptable than the control stems. This difference in color was also present when hue values were considered, except that the hue values for the control stems and the stems fumigated in the inserts were similar. Hue values for stems fumigated in the lug or bin were less than the values for control stems or insert fumigated stems and would be darker with more brown color making them (lug or bin) less acceptable.

Time in storage had a major influence on fruit and stem quality, regardless of fumigation treatment. As time in storage progressed, quality of both the fruit and stem was reduced. Quality loss of methyl bromide fumigated fruit and stems progressed at a more rapid rate than non-fumigated fruit and stems.

Residues
Organic methyl bromide residues declined rapidly after 6 hrs posttreatment from a high of 4.5 ppm to 1 ppb or less within 3 days posttreatment with two replications and to less than 1 ppb within 5 days with the third replication (Table 4). Inorganic bromide residues after fumigations were 4.5 to 5.3 ppm, and these are within the range previously found for other similarly treated cherry cultivars (Moffitt et al., 1983; Singh et al., 1976) and below the 20 ppm EPA tolerance (EPA, 1969).

Table 4. Organic bromide residues in 'Rainier' cherries fumigated in polypropylene plastic inserts with methyl bromide at 64 g/m3 for 2 hr at 6°C.
Treatmentb
Residues (ppm)a
Ave.±SD
Control
<0.001
6h
4 + 4 + 0.3
1 day
0.82 + 0.15
2 days
0.018 + 0.004
3 days
<0.010
5 days
<0.001

a
Data from nine analytical experiments.
bTime after treatment.

Fumigation of sweet cherries with methyl bromide in the polypropylene plastic inserts placed inside wooden bulk apple bins resulted in acceptable residue levels and the procedure subsequently has been approved for the treatment and shipment of all approved cultivars of sweet cherry to Japan.


Acknowledgment

We thank Judy Johnson (USDA-ARS, Fresno, CA), Paul Chen (OSU, Hood River, OR), and Wally Ewart (Northwest Horticultural Council, Yakima, WA) for reviewing this manuscript. Mention of a proprietary product does not constitute an endorsement by the USDA.

References Cited

EPA (Environmental Protection Agency). 1969. EPA compendium of registered pesticides: insecticides, molluscicides, and antifouling compounds. Vol. III, p. III-M-11.5. EPA, Washington, DC.

Hartsell, P.L., C.M. Harris, P.V. Vail, J.C. Tebbets, J.M. Harvey, V.Y. Yokoyama, and R.T. Hinsch. 1992. Toxic effects and residues in six nectarine cultivars following methyl bromide quarantine treatment. HortScience 27: 1286-1288.

Harvey, J.M., C.M. Harris, and P.C. Hartsell. 1989. Tolerances of California cultivars to methyl bromide quarantine treatments. J. Amer. Soc. Hort. Sci. 114: 626-629.

Hinsch, R.T., C.M. Harris, P.L. Hartsell, and J.C. Tebbets. 1992. Fresh nectarine quality and methyl bromide residues after in-package quarantine treatment. HortScience 27: 1288-1291.

King, J.R., C.A. Benschoter, and A.K. Burditt, Jr. 1981. Residues of methyl bromide in fumigated grapefruit determined by rapid headspace assay. J. Agric. Food Chem. 29: 1003-1005.

Moffitt, H.R., S.R. Drake, H.H. Toba, and P.L. Hartsell. 1992. Comparative efficacy of methyl bromide against codling moth (Lepidoptera: Tortricidae) larvae in 'Bing' and 'Rainier' cherries and confirmation of efficacy of a quarantine treatment for 'Rainier' cherries. J. Econ. Entomol. 85: 1855-1858.

Moffitt, H.R., J.B. Fountain, P.L. Hartsell, and D.J. Albano. 1983. Western cherry fruit fly (Diptera: Tephritidae): fumigation with methyl bromide at selected fruit temperatures. J. Econ. Entomol. 76: 135-138.

Monro, H.A.U. 1969. Manual of fumigation for insect control. 2nd edition. FAO-UN, Rome. SAS Institute. 1982. SAS user's guide: statistics. SAS Institute, Cary, NC.

Singh, G., L.E. Rippon, W.S. Gilbert, and B.L. Wild. 1976. Inorganic bromide residue in bananas, bell capsicums (sweet peppers), cherries and apples following fumigation with ethylene dibromide and methyl bromide. Aust. J. Exp. Agric. An. Husband. 16: 780-784.

Harold R. Moffitt(1), Stephen R. Drake(2), Dennis J. Albano(1), Preston L. Hartsell(3), Jane C. Tebbets(3), and James D. Hansen(1)

(1)USDA-ARS Yakima Agricultural Research Laboratory
(2)USDA-ARS Tree Fruit Research
(3)USDA-ARS Horticultural Crops Research Laboratory

Tree Fruit Postharvest Journal 10(1):10-14
February 1999

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