3175 Commercial Ave Northbrook, IL 60062 Phone: 847-840-1974

September 2001

Apricot Storage in Controlled Air

Report submitted to the Fruit Council by:

Susan Lurie and Assia Wexler, Storage Division, Volcani Institute

Yitzchak Kosto, Agricultural Extension Services, Agriculture Ministry

 Introduction

In Israel, one main variety of apricot is raised, the Raanana. Large quantities of Raanana ripen all over the country in the same two- to three-week period in June. In order to prevent a drop in prices and to lengthen market time, the fruit is stored at 0^o c. However, the optimal storage period wherein fruit quality is preserved lasts for up to three weeks only, depending on the physiological ripeness of the fruit at the time of picking.

Storage beyond this three-week period leads to the internal darkening of the fruit’s flesh. Studies conducted in the past have shown that storage in controlled air can lengthen the fruit’s storage period to five weeks without signs of damage to the flesh, providing that the level of CO₂is kept between 10% and 15%.

Last year, an experiment in prolonged storage was conducted at the Rafkor Packing House, where fruit baskets were individually sealed inside Xtend brand liner manufactured by Setpac, with the objective of creating a modified atmosphere inside the liner. The significance of the experiment was manifested in the high CO₂ level achieved during ventilated fruit storage. This year, we tried sealing entire bins (21 in all) inside giant liners in order to create a modified atmosphere inside the bin.

 Methods

Fruit was picked in a commercial-scale picking on June 28, 2001, and underwent refrigeration in forced air overnight in the Rafkor Packing House. Sixteen bins were chosen for the experiment. The fruit was bright yellow with a green seam. The bins were lined with various types of liners, and 18 cartons of fruit (eight kilograms of fruit packed into four plastic trays) were placed in each bin. The bins’ upper parts were covered and bound. Three cartons in one bin remained outside the liner as a control group for that bin. The treatment groups were as follows:

                     ·       Biofresh liners from Grofit Plastics Bio Fresh - four bins

                     ·       Polyethylene (PE) liners at a thickness of 70 microns - three bins

                     ·       Polyethylene (PE) liners at a thickness of 150 microns - three bins

                     ·       One bin in which fruit was placed on Xtend liners manufactured by Setpac, with each carton placed separately (as had been done the previous year)

                     ·       Five more bins were covered in a polyethylene sleeve at a thickness of 40 microns used for covering bins of pears; a single bin was covered by itself, and the four remaining bins were covered in pairs.

The temperature in the room where the bins were placed was 6.5^o c., and the temperature of the fruit was 2.5^o c. The bins were moved into storage at 0^o c. and kept there for 34 days until July 1, 2001. The air inside of each of the linings was analyzed on June 6^th, June 19^th, and on July 1^st immediately prior to opening. In the liners wherein the oxygen level had dropped below 2%, holes were made in the liners with a syringe.

            On July 1, 2001, three cartons of apricots were taken from each bin (two cartons that had been in a modified atmosphere and one carton from the control group) to the Volcani Center for testing.

The fruit was tested upon its removal, again two days later, and finally after an additional two days, the latter two tests being performed after the fruit had been stored at shelf temperature (20^o c.) for those four days. The properties tested for were:

1.     Internal and external damage - The degree of internal darkening (the main problem) was defined as either mild, medium, or severe.

2.     Decay

3.     Skin color on the “a” scale of a Minolta chromometer, and based on a visual ranking of greenish yellow, yellow, or bright yellow

4.     Firmness, using a Penifil penetrometer with a head 8 mm thick on peeled fruit samples

5.     Sugar level - Soluble Assimilated Quantity (SSC) in the juice of 10 apricots, using an Atago refractometer

6.     Acidity (TA) - The level of malic acid in the juice as measured by an automatic Metrohm titrator

 Three repetitions from each carton were performed on each testing date.

 Results

The treatments and the gas levels found in the bins are shown in Table 1.

The Grofit Plastics Bio Fresh liners maintained CO₂at levels below 20% and oxygen at a level over 2% throughout the storage period—the range of levels of CO₂ and of oxygen that we aimed for. Likewise, in the Xtend liners in the individual cartons, CO₂ levels between 10% and 15% were found. The oxygen levels were higher in the Xtend liners as compared to the Grofit Plastics Bio Fresh liners, because Xtend liners are microperforated (have tiny holes). In the PE liners, the desired modified atmosphere was not achieved.

In the liners of a 70 μ thickness, CO₂ levels exceeding 20% were produced, and the addition of microperforation did not bring down the CO₂ levels, but rather merely prevented their increase. It was not possible to seal the liners of a 150 μ thickness at the beginning of the experiment, and this is the reason for the differences between bins of the same treatment group. However, these liners also allowed the production of excessive levels of CO₂.

Upon removal from refrigeration, all of the fruit looked healthy except the fruit from the bin in which the CO₂ level was above 20%. This fruit showed brown bruise marks on its skin, a sign of CO₂ damage. In all of the treatment groups, the fruit’s skin was bright yellow, firm, and showed little decay (Table 2).

In most of the treatment groups, the firmness and acidity levels of the fruit were higher in the fruit stored in the modified atmosphere as compared to the control group fruit in regular air. Skin color and SCCs were similar in both the control group and the modified atmosphere groups.

The fruit from the Xtend-lined bins maintained higher levels of firmness and acidity than the fruit in the other treatment groups. There was little internal darkening in the fruit upon its removal from refrigeration except for the fruit in the bins lined with PE at a thickness of 150 μ, which showed slight darkening of the flesh (data not shown).

The quality of the fruit after two days’ and after four days’ storage at 20^o c. is shown in Tables 1 and Figure 3.

The fruit in all of the treatment groups in which a modified atmosphere was produced maintained its firmness, showed bright skin color, and showed lessened or delayed internal darkening and gel on the flesh. Decay was low in the fruit stored in the bins lined with Xtend and Grofit Plastics Bio Fresh liners, but not in the bins lined with PE liners, where damage was caused by the high level of CO₂.

Covering the bins in plastic for pears did not produce a modified atmosphere, and therefore did not offer the positive effects of the other coverings. High levels of internal darkening were found in this fruit after two days of shelf life, similar to the levels found in the control group.

 Conclusions

Two bins, those lined with Xtend and Grofit Plastics Bio Fresh liners, maintained the quality of their contents throughout the 34 days of storage at 0^o c., and for two more days of storage at 20^o c. of shelf life. In these treatment groups, the CO₂ levels achieved ranged from 10% to 20%. The fruit in these treatment groups maintained adequate firmness even after four days of shelf life. The decay level, darkening of the flesh, and the development of gel after two days of shelf storage at 20^o c. were low, if existent at all. In contrast, after four days of shelf storage, internal darkening was high, if lower than that in the control group.

It can be concluded that storage in modified atmosphere conditions results in higher quality fruit even after five weeks, yet allows a short shelf life.

We would like to thank the Rafkor Packing House staff for their assistance and their contribution to the conducting of this experiment.

  Table 1. Treatments and composition of gases inside the bags of apricots with modified atmospheres.

Treatment		CO2 levels			O2levels
	Date	17.6	19.6	1.7	17.6	19.6	1.7
	Repetition
Grofit Plastics Bio Fresh	1	11.3	15.8	19.7	6.1	2.6	2.4
	2	13.2	15.4	16.5	2.5	3.6	3.6
	3	12.4	12.8	16.9	4.3	7.5	5.1
	4	13.4	15.2	18.4	4.1	4.8	2.1
PE 70 μ	1*	11.1	22.8	23.1	9.5	2.7	2.1
	2*	14.0	22.7	28.2	5.3	2.1	1.0
	3*	15.3	18.9	21.7	2.6	2.8	2.3
PE 150 μ	1	7.2	7.54	10.3	13.3	13.7	12.9
	2	7.1	9.9	24.5	13.5	11.5	3.9
	3*	14.9	21.1	22.9	5.1	2.1	3.2
Xtend	1	15.3	13.9	15.0	3.1	9.4	9.5
	2	14.1	14.0	12.7	3.8	10.3	7.2
	3	12.9	13.8	12.2	7.2	9.2	9.8
	4	14.8	16.2	15.8	4.4	9.8	12.0
	5	10.9	12.4	15.0	8.4	9.8	11.0
	6	13.3	13.7	13.2	6.4	8.1	9.3
Pear PE	1			0.4			20.6
	2			0.6			20.6
	3			0.5			20.5

*The bags were perforated with a needle following the June 19^th testing. Between 20 and 30 holes were made.

 Table 2. Apricot quality after 34 days’ storage at 0^o c. in regular air or in a modified atmosphere.

Treatment	Firmness		SCC (%)		Acidity (%)		“a” color		CO2 damage
	air	MAP	Air	MAP	Air	MAP	Air	MAP
Grofit Plastics Bio Fresh	4.1	5.5	14.2	14.3	1.0	1.2	7.0	5.5
	6.8	6.5	13.1	14.6	1.1	1.1	2.9	7.9
	6.7	4.5	13.7	12.6	1.0	1.4	3.3	2.1-
	6.9	8.5	14.0	15.5	1.0	1.3	1.4	3.2
PE 70μ	7.2	8.5	13.3	13.5	0.95	1.3	1.9-	3.2	+
	7.7	8.4	13.7	13.2	1.1	1.3	2.8	3.2	+
	6.9	5.5	15.2	15.6	0.9	1.4	2.7	5.6
PE 150μ	6.9	6.3	15.2	14.2	0.9	1.4	2.7	2.7	+
	6.9	6.5	16.3	13.4	1.2	1.2	1.8	1.3	+
	5.8	7.8	15.0	13.4	1.0	1.7	1.0	0.6
Xtend		8.6		12.0		1.3		1.6
		8.7		12.9		1.4		2.6
		8.3		15.0		1.4		3.9-
		9.4		11.8		1.4		2.6
		7.9		13.9		1.4		3.5
		8.1		13.4		1.4		3.5-
								1.4
Pear PE	6.4		13.5		0.8		2.4
	6.5		12.3		1.2		0.8-
	6.2		12.6		1.0		2.6

Table 3. Apricot quality after two and four days’ storage at 20^o c.

Treatment Firmness(co re) Soft fruit (%) Yellow skin Bright yellow skin Decay (%) Darkening of flesh Gel on flesh   2 days 4 days 2 days 4 days 2 days 4 days 2 days 4 days 2 days 4 days 2 days 4 days 2 days 4 days                               Grofit Plastics Bio Fresh 5.3 5.0 16 30 27 78 2 0 0 4 12 40 0 5 Control group 4.2 3.8 29 92 12 50 4 50 6 30 75 98 10 22                               PE 70 5.7 4.7 19 33 23 91 4 9 0 20 22 51 0 20 Control group 4.6 3.6 -- 81 -- 33 -- 67 7 31 57 92 25 37                               PE 150 6.3 6.5 33 49 16 36 0 41 0 32 69 50 0 49 Control group 5.0 4.7 39 75 -- 100 -- 0 3 31 82 89 13 53                               Xtend 8.0 7.9 0 4 28 41 0 0 0 8 13 49 0 18                               Pear PE 5.1 4.4 25 77 25 90 0 0 5 28 78 91 0 41

 [Fig. 1 - could not copy]

Firmness, decay, and darkening of flesh in apricots after 35 days’ shelf storage