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Tuesday, August 22, 2017

WSU-TFREC/Postharvest Information Network/Ethylene Levels in Commercial CA and Low-Ethylene CA Storage of Golden Delicious, Starking, and Granny Smith Apples and Packham's Triumph Pears



Ethylene Levels in Commercial CA and Low-Ethylene CA Storage of Golden Delicious, Starking, and Granny Smith Apples and Packham's Triumph Pears


Abstract

Mean ethylene levels in commercial controlled atmosphere (CA) stores varied from 160 to 550 ppm with a maximum of 1400 ppm in one room. Simulated CA storage of Golden Delicious, Starking, and Granny Smith apples and Packham's Triumph pears at atmospheres containing low and high ethylene levels indicated that high ethylene levels did not appreciably affect fruit quality during storage periods of less than 9 months. After 9 months, fruit stored at high ethylene levels were slightly softer, more yellow, and contained less acid and total soluble solids than fruit in low-ethylene atmospheres. Granny Smith apples in high-ethylene atmospheres developed core flush when the storage period exceeded 5 months. Fruit quality was more affected by storage temperature than by ethylene level. Even after a storage period of 9 months at 4°C, no ethylene-related changes in the quality of Golden Delicious or Packham's Triumph were noted.

Introduction

The rate of ethylene evolution by fruit is affected by temperature, oxygen concentration, and carbon dioxide concentration (1). Minimum temperatures at which ethylene loses its effect as a ripening hormone are not known. However, for most fruit there is no evidence that ripening will be initiated at 0°C. Below 12°C, ethylene is produced very slowly (1). The optimum temperature for ethylene production is 30°C for apples, 32°C for some plum cultivars, and 20°C for peaches, nectarines, and pears. Ultra-low oxygen and elevated carbon dioxide concentrations suppress ethylene production by apples (11, 15) and pears (24).

Fruit quality can be affected by high ethylene levels during CA storage. Ethylene removal retards softening of Bramley's Seedling (5, 6) and Macintosh apples (2, 9, 10, 12). These reports are mostly based on studies with Macintosh apples from daminozide-sprayed trees which might have affected the results. Furthermore, the storage temperature was 3 to 5°C. Granger and Rouselle (4) reported similar results for Macintosh apples stored in regular atmospheres. Firmness of Schone von Boskoop apples was not affected by ethylene scrubbing (23). Ethylene removal can decrease the incidence of disorders such as scald (6, 18), bitter pit (18), and core flush (8) although Schone von Boskoop developed more core flush at 1% oxygen when the ethylene was scrubbed (17). Scrubbing ethylene from the atmosphere can therefore modify the potential for development of disorders (18).

Granger and Rouselle (4), Lange (7), and Streif (21), on the other hand, found no benefit in removing ethylene from storage atmospheres and Lougheed et al. (14) reported that lowered ethylene concentrations often, but not always, coincided with firmer fruit. Lowering of the oxygen concentration diminished the detrimental effect of high ethylene levels (11). In South Africa, apples and pears are CA stored at temperatures ranging from -0.5 to 0.5°C and oxygen concentrations of 1.0 and 1.5%. Ethylene levels in CA rooms can increase as a result of respiration as well as incomplete combustion when catalytic converters are used to establish and maintain low oxygen concentrations. The effect of high ethylene levels on fruit cannot be predicted from available literature alone.

Ethylene levels in commercial CA stores were monitored and an investigation was conducted over a 3-year period to establish whether high and low ethylene levels affected fruit quality during simulated CA storage at storage temperatures ranging from -0.5 to 4°C.


Materials and Methods

Ethylene levels in commercial CA stores
A survey of ethylene levels in commercial CA stores was done over one season by collecting air samples from 50 commercial CA stores once a month for 6 months. The stores contained fruit of all apple and pear cultivars normally stored under CA conditions. A sample of 5 ml of air was collected in a gas-tight syringe and 0.75 ml was injected into a gas chromatograph (Varian Model 3300) fitted with a Porapack Q column (3 mm x 2 m) and flame ionization detector. Injection port and column temperatures were 120°C and 60°C, respectively.

Effect of ethylene on fruit quality at -0.5°C
Fruit of the apple cultivars Golden Delicious, Starking, and Granny Smith and the pear cultivar Packham's Triumph packed in 10 kg plastic containers were pre-cooled immediately after harvest and placed in a 1000-liter experimental CA chambers at -0.5°C (Golden Delicious, Starking, and Packham's Triumph) and 0.5°C (Granny Smith). Starking, Granny Smith, and Packham's Triumph were treated before storage with 1000 ppm diphenylamine to control superficial scald. Atmospheres in the chambers consisted Of 1% O2 and 1% CO2 (Starking), 1.5% O2 and 1.5% CO2 (Golden Delicious, Packham's Triumph) and 1.5% O2 and 0% CO2 (Granny Smith). These conditions were attained within 1 day after the chambers were sealed by flushing the atmosphere with liquid nitrogen until the desired concentration was reached. Gas concentrations were verified twice a day by means of a paramagnetic and infrared analyzer and maintained with a 0.1% variation. Calcium hydroxide (25 kg) was placed in each chamber containing Granny Smith apples to maintain the concentration at 0% CO2. In other chambers, CO2 accumulation was controlled by circulating the air through a Ca(OH)2 solution when required. Ethylene levels were maintained at approximately 1 and 1000 ppm. Concentrations were verified by gas chromatography and adjusted by either circulating the air through KMnO4 or by adding ethylene gas to the storage atmosphere. The experimental design was a completely randomized design and the experiment was done during two consecutive seasons. Five 10 kg containers of fruit per ethylene level per cultivar were removed for evaluation after 5, 7, and 9 months and stored at a simulated marketing temperature of 20°C for 1 week prior to evaluation.

Effect of ethylene on fruit quality at elevated temperatures
Golden Delicious and Packham's Triumph fruit were pre-cooled immediately after harvest and placed in 1000-liter experimental CA chambers at -0.5, 1.0, 2.5 and 4.0°C. The CA conditions used were similar to those used in the previous experiments. At each temperature, ethylene levels were maintained at 1 and 500 ppm as previously described. Experimental design was a completely randomized 2 x 4 factorial (ethylene level x storage temperature). Five 10 kg containers of fruit per ethylene level per storage temperature were removed for evaluation after 5, 7, and 9 months and stored at a simulated marketing temperature of 20°C for 1 week prior to evaluation.

Evaluation
Fruit firmness, skin and seed color, total soluble solids, and titratable acidity were evaluated according to the methods used by Truter et al. (22) after each storage period. The incidence of superficial scald on Starking and core flush in Granny Smith apples was also recorded as a percentage of the total number of fruit per container.

Parametric data were subjected to one- and two-way analysis of variance and non-parametric data to Kruskal-Wallis analysis of variance (19).


Results and Discussion

Ethylene levels in commercial CA stores
The mean ethylene concentration in rooms where Golden Delicious apples were stored was 550 ppm and in one room the concentration was higher than 1400 ppm. The mean for Starking was 250 ppm, for Granny Smith slightly higher than 200 ppm, and for Packham's Triumph 160 ppm. Golden Delicious apples therefore apparently produced more ethylene during CA storage than the other two apple cultivars. Similar results were obtained where Golden Delicious and Starkrimson apples were compared (3). Fidler (16) reported peak concentrations of 100 to 150 ppm in apple CA stores with 600 ppm as the highest recorded value. In the present study, the ethylene level used in the first laboratory trials was chosen arbitrarily and was much higher than concentrations detected in commercial stores. In subsequent trials the level was adjusted to 500 ppm.

Effect of ethylene on fruit quality at -0.5°C
As similar trends were observed during both seasons studied, results of only one season are presented. Golden Delicious apples exposed to 1000 ppm were significantly less firm and slightly greener than control fruit while other cultivars were unaffected during a 5-month storage period (Table 1). Only the color of Golden Delicious was adversely affected by high ethylene levels during 7 months' storage at -0.5°C. However, during a 9-month storage period, Golden Delicious apples and Packham's Triumph pears stored in a high-ethylene atmosphere were significantly less firm and more yellow than control fruit (Table 1). The total soluble solids of Golden Delicious and Granny Smith apples and titratable acidity of Golden Delicious also decreased slightly during 9 months' storage. Stow (20) reported very little degreening of Cox's Orange Pippin apples during a storage period of 5 months in atmosphere containing high ethylene levels, but apples were markedly degreened after a storage period of 8 months.

The mean incidence of superficial scald in Starking apples was 7.4, 15.3, and 41.8% after 5, 7, and 9 months' storage, respectively, and was not affected by ethylene level. Liu (9) reported similar results for other red cultivars. The incidence of core flush in Granny Smith apples exposed to 1000 ppm ethylene increased significantly to 10% and 16% after a storage period of 7 and 9 months, respectively. Core flush in Macintosh (2) and Australian-grown Granny Smith apples (8) also increased at high ethylene levels.

Ethylene therefore had only a slight effect on fruit quality during storage periods of 5 and 7 months, although the effect was more noticeable after 9 months. Starking apples were least affected. This is probably due to the low storage temperature and oxygen concentration used.

Effect of ethylene on fruit quality at elevated temperatures
Only results obtained after a storage period of 9 months are presented as ethylene level and storage temperature had only a negligible effect during shorter storage periods. Even after 9 months no trends were discerned that could be related to ethylene level (Table 2). At a storage temperature of -0.5°C, 500 ppm ethylene caused softening of Golden Delicious apples and Packham's Triumph pears. Some softening of Packham's Triumph also occurred at 2.5°C. Total soluble solids of Golden Delicious decreased at a temperature of -0.5°C, while that of Packham's Triumph increased at -0.5 and 2.5°C. Titratable acidity remained unaffected.

The mean color ratings of Golden Delicious apples increased significantly from 4.6 to 5.3 after 5 months, and from 5.7 to 6.2 after 7 months. After 9 months, differences in color ratings were nonsignificant. Packham's Triumph pears stored at 4°C ripened unevenly and some did not ripen at all. Fruit quality was therefore more affected by storage temperature than by ethylene level. These results confirm those of Fidler who found that ethylene concentrations as high as 600 ppm did not cause ripening of apples at temperatures of 34°F (1.1°C) to 37°F (2.8C) (16).


Conclusions

Fruit quality was more affected by storage temperature than by ethylene level. High ethylene levels slightly affected fruit quality at storage temperatures from -0.5 to 4.0°C after storage periods of up to 7 months, although the effect was more pronounced after 9 months. Ethylene levels in commercial CA stores were lower than those used in these trials. There is therefore no major risk that ethylene levels which normally occur in commercial CA stores will cause substantial losses in fruit quality. However, during long-term storage build-up of ethylene in cold stores must be monitored to prevent levels in excess of 1000 ppm.


Acknowledgement and Address

(This article was adapted with permission from an article in the Proceedings of the Fifth International Controlled Atmosphere Research Conference, June 14-16,1989, Wenatchee, WA. pp. 333-339. Due to space limitations, references have been omitted. They may be obtained from the editors.)

Address: Fruit and Fruit Technology Research Institute, Private Bag X5013, Stellenbosch 7600 Republic of South Africa


Tables 1 and 2

Table 1. Effect of ethylene in the storage atmosphere on the quality of apples and pears during controlled atmosphere storagea at -0.5°C for 5, 7, or 9 months followed by 7 days at 20°C.

Fruit firmness (N)
Cultivar C2H4 concentration (ppm) 5 months7 months9 months
Golden Delicious 164.955.659.2
100061.861.452.5
Significanced ***
Starking 172.569.465.4
100074.366.363.2
SignificanceNSNSNS
Granny Smith 166.763.664.9
100067.262.771.2
Significance NSNS*
Packham's Triumph 123.623.128.9
100027.624.09.8
Significance NSNS*
Colorb (Rating)
Cultivar C2H4 concentration (ppm) 5 months7 months9 months
Golden Delicious 14.65.45.2
10004.06.06.5
Significance ***
Starking 13.43.63.4
10003.43.63.6
SignificanceNSNSNS
Granny Smith 13.33.43.5
10003.43.33.6
Significance NSNSNS
Packham's Triumph 13.53.63.3
10003.33.54.1
Significance NS**
TSS (°Brix)b
Cultivar C2H4 concentration (ppm) 5 months7 months9 months
Golden Delicious 115.214.314.4
100015.115.213.6
Significance NS**
Starking 113.213.213.5
100013.514.214.1
SignificanceNS*NS
Granny Smith 113.514.113.6
100014.013.813.1
Significance *NS*
Packham's Triumph 113.014.412.0
100013.812.013.3
Significance NS**
Titratable
acidity (%)
Cultivar C2H4 concentration (ppm) 5 months7 months9 months
Golden Delicious 10.260.250.29
10000.270.270.25
Significance NSNS*
Starking 10.200.200.22
10000.190.200.21
SignificanceNSNSNS
Granny Smith 10.380.350.36
10000.350.350.34
Significance NSNSNS
Packham's Triumph 10.130.130.12
10000.140.150.11
Significance NS*NS
 
aSee text for O2 and CO2 concentrations.
bGround color changes from green to yellow as ratings increase.
cMonths in storage.
dNS=statistically nonsignificant; *=significant at 5% level.



Table 2. Effect of ethylene in the storage atmosphere on the firmness, total soluble solids, and titratable acidity of apples and pears during controlled atmosphere storage (1.5% O2, 1.5% CO2) at different temperatures for 9 months and 20°C for 7 days.

Cultivar Temperature °C Fruit firmness(N) TSS (°Brix) Titratable acidity(%)
Ethylene (ppm) Ethylene (ppm) Ethylene (ppm)
15001500 1500
Golden Delicious -0.559.2a53.0cd14.3a 13.4b0.28a0.25a
1.051.2de53.4bc14.9a 14.7a0.23a0.25a
2.550.3c50.7e14.2a 14.2ab0.27a0.25a
4.053.4bc54.7b14.7ab 14.8a0.24a0.26a
Packham's Triumph -0.531.2a16.5e12.0b 13.0a0.11a0.11a
1.016.0e21.4bc13.5a 13.1a0.10a0.11a
2.522.2b19.1cd11.4c 12.1b0.13a0.12a
4.017.3de18.7cde13.3a 13.5a0.12a0.14a
Means in columns within a cultivar and quality parameter followed by the same letter do not differ significantly according to Tukey's Test (P=0.05).

A. B. Truter and J. C. Combrink

Fruit and Fruit Technology Research Institute

Tree Fruit Postharvest Journal 4(3):14-18
October 1993

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