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Avocado Storage Results

Avocado Storage Results

Results of storing avocado in modified atmosphere packaging

Fruit Storage Research Laboratory

Kiryat Shmona 10200

Storage of Avocado Fruit in Modified Atmosphere Packaging

Fruit Laboratory: 

O. Nerya, A. Gizis,A. Zvilling, N. Ezov, R. Fogel-Sagee, A. Sharabi-Nov, R. Ben-Arie

Avocado-Gal:  Y. Mizrahi Shaham

Ministry of Agriculture:  M. Noi

 

Introduction

Preliminary observations and personal contacts (Ami Kenan –Zemach Packing House) seem to indicate that if avocado are packaged in Bio Fresh Bags, manufactured by adding an ethylene absorbent to polyethylene at Grofit Plastics, the fruit can maintain its external and internal quality for more than 3 weeks.  These findings are supported by previous works that proved the efficiency of storage in a modified atmosphere (Reznitsky and Ziv, 1989; Meir et al., 1995) and by a recent report claiming that ethylene assists in the grey discoloration of avocado pulp.

The objective of this study was to enable the storage of avocado, the Fuerte and Hass varieties, for at least 5 weeks post-harvest and to obtain firm, healthy fruit without internal discoloration that would ripen satisfactorily during shelf life.

Two trials were conducted, one for each variety, at the beginning of March, at the Avocado-Gal Packing House.

The Method

Fuerte – Size 14 avocados were sorted, waxes and dried on March 5, 2000, one day after being harvested at three sample orchards:  Snir, Dan and Mahanaim.  The packaging treatments were as follows:

  1. Control Group – bare fruit
  2. Bio fresh bags – folded
  3. Bio fresh bags – tied

 

The fruit was stored at a temperature of 6ºC for either 32 or 39 days.  The average temperature of the fruit in the unpadded boxes was 6.0 ± 0.4ºC and 6.3 ± 0.1ºC in the padded boxes.  After each storage period, four boxes from each type of treatment and from each of the orchards were sent to undergo shelf life conditions, at a temperature of 20ºC, for a period of 5 days.  The fruit was removed from half of the bags prior to sending them to the shelf life environment.  The remaining bags were sent at a temperature of 20ºC for a period of 5 days without being opened and were kept for an additional 5 days after being opened.  In all of the instances, the composition of the atmosphere within the bags, including the ethylene level, was tested prior to opening.

Upon removal from cold storage, the quality of the fruit in the opened bags was evaluated and three pieces of fruit were cut lengthwise to assess their internal condition.  The assessment of the fruit included:  weight loss, decay, marketability, firmness.  After shelf life, all of the fruit was cut in order to assess discoloration.

 

Hass – Size 18 avocados were avocados were sorted, waxes and dried on March 6, 2000, one day after being harvested at two sample orchards:  Amiad and Daphna.  The packaging treatments were as follows:

1.      Control Group – bare fruit

2.      Bio fresh bags – folded

3.      Bio fresh bags – tied

4.      LDPE bags (Low Density Polyethylene) – folded

5.      LDPE bags  (Low Density Polyethylene) – folded

The fruit was stacked on pallets and stored in the commercial warehouse of the packing house at a temperature of 6ºC.  Sample boxes (1-5/treatment/orchard) were sent to the Fruit Laboratory after 6 and 7 weeks.  Upon removal from storage, the atmosphere in the bags was evaluated, the bags were opened and the fruit was examined as previously described, prior to being sent for shelf life.  In addition, the color of the fruit was evaluated and noted as green, altering in color, or brown.

 

Results

Figure 1:  O2 and CO2 levels in folded and tied bio fresh bags after being stored at 6ºC and for 5 days of shelf life at 20ºC.

Fuerte

The composition of the atmosphere within the folded and tied bags is described in Fig. 1. The levels of O2 in the folded bags that had exceeded 15% during storage dropped below 10% during shelf life.  The level of CO2 increased to 3% during storage and exceeded 5% during shelf life.  In the tied bags, oxygen levels were generally between 5-7% during storage and between 3-4% during shelf life.  The level of CO2 rose to 6% and to 7-8%, respectively.  Ethylene accumulation in the bags was below the level of detection (10ppb) during both storage and shelf life.

 

Weight Loss

The weight loss of the fruit in the Bio Fresh bags was significantly reduced, in comparison to the control group (Table 1), regardless of the method of closing the bags.  Moreover, there was no increase in the weight loss of the fruit in the bags during the last week of storage, in comparison to the accelerated rate noted for the fruit that was not in bags.

 

Table 1:  Percentage of weight loss of Fuerte avocados stored at 6ºC (initial weight -287 gr)

Treatment

Stored for 32 days

Stored for 39 days

Control Group

3.9a

5.1a

Bio Fresh – folded

1.2b

1.2b

Bio Fresh – tied

0.9b

0.9b

The quality of the fruit after removal from storage

 

After being stored for 32 days, the fruit from all of the treatments was firm and appeared well.  In other words, it was marketable.  However, only 30% of the fruit from the control group and the folded bags did not have pulp discoloration (Table 2).  After an additional week in storage, only the fruit in the tied bags remained firm and marketable, but there was a slight increase in the extent of discoloration.

 

After removing the fruit from the bags and sending it shelf life conditions, the fruit from the tied bags softened. It also decayed to a considerable extent, although less than the fruit from the control group.  Although most of the fruit (from all of the treatments) suffered from pulp discoloration, it was less severe in comparison to the fruit that had been stored in tied bags.

 

In the bags that remained tied during the 5 days of shelf life, the level of CO2 rose to 8% and the oxygen level dropped to 3% (Fig. 1), without any accumulation of ethylene.  The fruit did not soften or decay under these conditions.  But, there was an increase in pulp discoloration, particularly after the fruit was removed from the bags, and the fruit soften quickly.  The fruit that remained in the folded bags during shelf life softened even more rapidly and the signs of decay and discoloration were more extensive in comparison to the fruit in the control group that had not been in bags (data not presented).

 

 

 

 

 

 

 

 

 

 

Table 2:  Quality of Fuerte avocados upon removal from storage at 6ºC and after 5 days of shelf life at 20ºC (without bags)

Storage in Days

  6oC         20oC

Treatment

Firmness*

Decay (%)

Marketable (%)

Healthy pulp (%)

Discoloration index **

32

0

Control

3.37b

0

100a

30.6b

1.46a

 

Bio-Fresh, folded

3.48b

0

100a

30.6b

1.54a

Bio-Fresh, tied

4.00a

0

100a

52.8a

1.18b

32

5

Control

1.33b

84.1a

15.9a

11.1a

2.56a

 

Bio-Fresh, folded

1.33b

83.2a

1.5a

10.9a

2.50a

Bio-Fresh, tied

2.61a

34.2b

25.3a

11.2a

1.62b

39

0

Control

2.05b

8.8a

38.6b

7.7

2.33

 

Bio-Fresh, folded

2.05b

0.0b

29.8b

--

--

Bio-Fresh, tied

4.00a

0.6b

95.4a

5.6

1.61

39

4

Control

1..04b

60.4a

33.5b

3.5a

3.12a

 

Bio-Fresh, folded

1.13ab

70.1a

38.0b

4.8a

3.05a

Bio-Fresh, tied

1.31a

4.6b

95.8a

6.7a

2.05

* Firmness index: 4 = firm fruit

** Discoloration index: 1= slight (up to 25%), 2=moderate  

a-b:  Different letters indicate significant differences between numbers in the same column

 

 

 

Hass

(The results for this part of the experiment are incomplete due to the loss of samples from the warehouse and the inclusion of fruit from another variety, by mistake).

During the two months of storage, the level of CO2 in the tied, Bio Fresh bags increased to 6-7%, while the O2 level decreased to 7-9% and the amount of ethylene accumulation remained very slight (Table 3).  In comparison, the level of CO2 in the tied PE bags was lower and the levels of O2 and ethylene accumulations were higher.  Without a doubt, these differences in the composition of the atmosphere surrounding the fruit were the primary cause for the difference in the quality of the fruit, as noted by the extent and the severity of pulp discoloration (Table 4).  This was also the main factor responsible for the deterioration in the quality of the fruit during the seven weeks of storage.  Aside from this, the fruit remained firm and apparently marketable.

For the most part, after the eight weeks of storage, the fruit that had not been placed in bags (the Control Group) was either soft or softening upon its removal from storage.  On the other hand, the fruit in the bags was still firm.  From the external appearance of the fruit it appeared that it was still marketable, but internal conditions indicated extensive pulp discoloration, which had only been very slight in the fruit stored in the tied, Bio Fresh bags.  After six days of shelf life, the fruit from all of the treatments was soft with severe pulp discoloration and about half of it was not suitable for consumption.

Table 3:  Composition of the atmosphere in packaging containing the Hass variety, upon removal from storage at 6ºC

Package type

Storage (days)

O2 (%)

CO2 (%)

Ethylene (ppb)

No. of replicates

Bio-Fresh, folded

48

18.2

2.4

--

10

56

18.3

2.5

ND

4

Bio-Fresh, tied

48

6.9

7.2

--

9

56

9.0

6.0

50

5

LDPE, tied

48

14.4

5.2

--

2

56

15.5

5.0

1500

4

ND = Not Detectable

       Table 4:  Quality of Hass avocado upon removal from storage at 6ºC and after shelf life at 20ºC (without bags)

Storage in  Days  

      6oC                 20oC

Treatment

Firmness*

Decay (%)

Marketable (%)

Healthy pulp (%)

Discoloration index **

48

0

Control

3.58a

1.86a

100a

5.0ab

2.13a

 

Bio-Fresh, folded

3.72a

1.90a

98.9a

4.0ab

2.31a

Bio-Fresh, tied

3.89a

1.48a

99.4a

26.7a

1.15b

LDPE tied

4.00a

1.69a

100a

0b

1.90ab

48

4

Control

1.65A

2.62A

100A

0A

3.81A

 

Bio-Fresh, folded

1.45A

2.53A

99.2A

2.3A

2.53B

Bio-Fresh, tied

1.62A

2.51A

89.1A

8.8A

1.53C

LDPE tied

1.56A

2.50A

100A

0A

2.62B

56

0

Control

2.00b

2.06a

100a

0b

4.00a

 

Bio-Fresh, folded

3.89a

2.10a

100a

0b

1.85bc

Bio-Fresh, tied

4.00a

1.70a

100a

11.5a

1.32c

LDPE folded

3.96a

2.01a

100a

0b

2.27b

LDPE tied

4.00a

1.63a

100a

0b

2.24b

56

6

Control

1.30A

2.78A

60.8A

0A

4.00A

 

Bio-Fresh, folded

1.39A

2.72A

49.5A

0A

3.69A

Bio-Fresh, tied

1.59A

2.58A

61.5A

0A

1.99b

LDPE folded

1.33A

2.41A

26.1A

0A

3.05AB

LDPE tied

1.37A

2.31A

32.2A

0A

2.21B

* Firmness index: 4 = firm fruit, 1 = soft fruit

** Peel color index:  1 = green, 2 = green + brown, 3 = brown

** Discoloration index: 1= slight (up to 25%), 2 = moderate (25-50%), 4 = severe (more than 50% of the surface area)  

a-b: Different letters indicate significant differences between numbers in the same column, while p < 0.05

 

Summary

Apparently, there is potential for extending the storage period of Fuerte and Hass avocados to 5 and 6 weeks, respectively, by storing them in a modified atmosphere inside Bio Fresh bags.  This is notable, in spite of the far from superior quality of the Fuerte avocados after 5 days of shelf life, following a storage period of 32 days at 6ºC, which showed decay and pulp discoloration.  The fruit used in this experiment was among the final pick of the season, known for its inferior storage quality.  The modified atmosphere packaging improved the quality of the fruit in comparison to the control group and one can expect excellent results from fruit harvested earlier in the season and stored under similar conditions.  This assumption will be examined in the upcoming season.

Avocados from the Hass variety adequately maintained their external appearance during the seven weeks of regular storage, as well as during the subsequent shelf life.  However, upon removal from storage, considerable amounts of internal discoloration were noted.  The extent and severity of pulp discoloration noted on the fruit that had been stored in tied Bio Fresh bags was less, but it was not a sufficient decrease.  From the rapid deterioration that occurred during an additional week of storage it can be deduced that the quality of the fruit stored in tied Bio Fresh bags would have been satisfactory after only 5-6 weeks of storage.  The accumulation of CO2 in the tied LDPE bags (5%) delayed the softening of the fruit, but the occurrence of pulp discoloration was not inhibited.  Pulp discoloration was clearly reduced as a result of ethylene absorption and the accumulation of CO2. (Discoloration occurred in the folded bags in which there was no ethylene and the CO2 level only reached 2.5%).  These findings are supported by Meir et al. (1995) who showed that the storage of avocado in a modified atmosphere with a CO2 level of 8% prevented discoloration at varying oxygen levels.  Although ethylene levels were not measured, their experiment was conducted in a flow-through system in which ethylene would not have accumulated.  This is possibly the explanation for the high quality of the fruit after seven weeks of storage.

From the perspective of commercial application, it is important to emphasize the need to remove the fruit from the bags prior moving it from a low to a high temperature.  In the experiment detailed above, the quality of the fruit was assessed only after 5 days at 20ºC in tied bags and the damage was severe.  In future trials, the quality of the fruit will need to evaluated after shorter periods of shelf life in order to determine the recommended timing for removing the fruit from the bags.

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