effect of carbon dioxide-enriched atmosphere …ahmed, 2001; kader, 2002; and al-redhaiman, 2005)....

JKAU: Met., Env. & Arid Land Agric. Sci., Vol. 20 No. 1, pp: 3-22 (2009 A.D. / 1430 A.H.)

3

Effect of Carbon Dioxide-Enriched Atmosphere during

Cold Storage on Limiting Antioxidant Losses and

Maintaining Quality of ‘Barhy’ Date Fruits

D.A. El-Rayes

Department of Plant Production and Protection,

College of Agriculture and Veterinary Medicine,

Qassim University, Al- Qassim, Kingdom of Saudi Arabia

[email protected]

Abstract. Mature ‘Barhy’ date fruits (Phoenix dactylifera L.) were

stored under different storage temperatures (0, 2, 4, 6°C) under

modified atmosphere (MA) conditions with 0.03, 5, 10, or 20% carbon

dioxide concentrations (balance air). Fruit total phenolic content

(TPC), flavonoids content, carotenoids content, total sugar %, SSC %,

and fruit skin color (L*a*b*c* and h*) were determined. Total

phenolic content (TPC) was determined by the Folin-Ciocalteu

method, and antioxidant capacity was determined using ferric

reducing antioxidant power (FRAP). A clear integration was observed

between modified atmosphere and cold storage treatments regarding

maintaining fruit quality during the storage period. Fruits stored under

low temperature conditions (0°C) or relatively high CO2 concentration

(20% CO2) did not show any chilling or CO2 injury symptoms. Fruits

kept under MA conditions with 20% CO2 at cold storage (0°C)

showed brightest yellow color, and highest storage ability among all

stored fruits. All MA conditions investigated extended date storability

by maintaining fruit quality. The effect of MA conditions on

maintaining fruit quality was magnified when fruits were stored under

cold temperature. Fruit quality was maintained for 173 days when

stored in 20% CO2 at 0°C, whereas it did not exceed 60 days when

stored under common air composition (containing 0.03% CO2) at 0°C.

Treatments with high CO2 concentrations (20% CO2) under cold

storage conditions (0°C) maintained fruit total phenolic content,

SSC%, total sugar content, and total tannins.

D.A. El-Rayes

4

Keywords: Barhy date fruits, Phoenix dactylifera L., modified

atmosphere, cold storage, fruit quality, total phenolic

content (TPC), antioxidant activity.

Introduction

Date palm is the major fruit tree in most Arabian Gulf countries and it is

widely grown in the middle-eastern countries. ‘Barhy’, one of the most

popular cultivar worldwide, is marketed and consumed at the full mature

stage of development (Bisr or Khalal). However, its economical value

decreases sharply when it ripens as surplus production has to be sold at

lower prices. Some trials have been carried out to maintain fruit quality

during storage of dates, including coating with polypropylene films

(Thompson and Abboodi, 2003), or using polyethylene bags (Attia, et al.,

1997). However, responses to these treatments have been limited.

Temperature is the environmental factor that most influences the

deterioration rate of harvested commodities. Temperature management is

the most effective tool for extending the shelf life of fresh horticultural

commodities (Kader, 2002). Some trials have been carried out to

maintain dates fruit quality during storage by using low temperature

(Hassan and El-Sheemy, 1989 and Hegazy, et al., 2003), however, no

published research are available indicating the optimum storing

temperature for Barhy dates at full mature stage.

The use of elevated CO2 at storage atmosphere for preserving fruit

quality and delaying fruit deterioration has been described (El-Rayes and

Ahmed, 2001; Kader, 2002; and Al-Redhaiman, 2005). Elevated

concentrations of CO2 inhibited decay and retarded softening without

impairing the flavor of many fruits (Kader, 2002). Moreover, CO2

significantly inhibited botrytis in Red Globe table grapes (Carlos, et al.,

2002). Although the effect of modified atmosphere (MA) treatments on

quality preservation of dried date fruit has been studied (Navarro, et al.,

1998), no information about responses of soft fully mature dates is

available.

Interest in phytochemical content and antioxidant activity of fruits

and vegetables has been very high in recent years. Recent studies have

shown that the majority of antioxidant activity in fruits or vegetables may

originate from the polyphenolic compounds (Wang, et al., 1996).

Effect of Carbon Dioxide-Enriched Atmosphere… 5

Date fruits are an excellent source of phenolics and therefore possess

an extremely high antioxidant capacity. The presence of phenolic

compounds in fruits and vegetables has been studied fairly well. In

addition to their important functions in plant defense mechanisms and

external stresses (Wang, et al., 1994), they also affect the quality, color

and taste of fruits and their products like juice and fruit slice (Van der

Sluis, et al., 2002). In low concentration, phenolics may protect food

from oxidative deterioration; however at high concentration, they (or

their oxidation products) may participate in discoloration of foods. For

example, the brown color development (known as enzymatic oxidation)

is mainly due to the polyphenol peroxides (PPO) activity and the amount

of the polyphenol substrates. As shown for apple fruits, the coloration

after oxidation depends on the balance between the phenolics:

hydroxycinnamics, and flavonols (Frankel, 1995).

Flavonoids exist widely in the plant kingdom and are especially

common in leaves, flowering tissues and fruits (Larson, 1988). Plant

flavonoids are an important part of the diet because of their effects on

human nutrition (Frankel, 1995).

Known properties of the flavonoids include: free radical scavenging,

and strong antioxidant activity (Frankel, 1995). Some evidence suggests

that the pharmacological effects of flavonoids are correlated with their

antioxidant activities.

The objective of this study was to evaluate the possibility of using

modified atmosphere conditions with high carbon dioxide-enriched under

relatively low temperature to maintain fruit quality and extend storage

ability of Barhy date fruits at full mature stage of development.

Materials and Methods

Plant Material

Fifteen years old ‘Barhy’ date palms (Phoenix dactylifera L.)

grown at the Research and Experimental Station, College of Agriculture

and Veterinary Medicine, Qassim University, Buraydah, Al-Qassim, the

Kingdom of Saudi Arabia, were selected for the study. All palms were

mature, of the same age and almost uniform in growth. The palms were

in good physical condition, free from insect damage and diseases and

were subjected to the same horticultural management treatments.

D.A. El-Rayes

6

Fruits were harvested at full mature stage, according to skin color

(the whole fruit should be yellow, and the yellowish green area should

not exceed 10%) and the percentage of soluble solids content (SSC%)

greater than 28% (Hegazy, et al., 2003). Immediately after harvest, fruits

were transported to the postharvest laboratory where those fruits of

similar shape, color, and degree of development were divided into groups

and were wiped free of dirt.

Treatments

Fruits were divided into 16 groups, each group representing a

different treatment. These treatments included four different storage

temperatures (0, 2, 4, and 6 + 2°C), each of storage temperatures was

divided into 4 groups, each group received one of the following CO2

treatments: 5%, 10%, 20% or 0.03% CO2, which represents room

ambient air.

Five replicates of each treatment were stored in well sealed gas

tight glass containers equipped with inlet and outlet valves, and CO2

was injected from gas cylinders to provide concentrations of 5%, 10%,

or 20% CO2 in air. Supply and exhaust CO2 gas composition was

monitored using a gas chromatograph (Carle Analytical series S, NY,

USA).

Analyses

Monthly samples (ten fruits per replicate) were removed and

frozen immediately for determinations of total tannin, sugars (total,

reducing and non-reducing), and SSC% contents. Each treatment was

terminated when the number of ripe fruits in each spike exceeded the

number of the unripe fruit.

SSC% was measured with a temperature compensated RFM 110

Bellingham + Stanley LTD refractometer (Lawrenceville, GA, USA).

Reducing and non-reducing sugars were determined colorimetrically

according to Dubios, et al. (1956) using Perkin Elmer Ez301 spectro-

photometer (Shelton, CT, USA). Total tannin content was determined

according to A.O.A.C. (1975). At the end of the experiment, fruit peel

color was measured by using Lovibond Tintometer GmbH.


Antioxidants and Phenolics Extraction Method

There are no satisfactory solvent extraction methods suitable for the

isolation of all classes of food antioxidants and phenolics or even for a

specific class of these components. This is due to the chemical nature of

food antioxidants and phenolics, which vary from being simple to being

very highly polymerized (Shahidi and Naczk, 2004). Therefore, the

extraction of antioxidant compounds and total phenolics for untreated

fruits was carried using five different solvents which have been used in

other studies (Ou, et al., 2001; Vinson, et al., 2001; Kalt, et al., 2001;

Huang, et al., 2002). The fruit sample was extracted using 40 ml of

water, phosphate buffer 75 mM, pH 7.4, ethanol (containing 0.1% formic

acid), or ethanol: water(1:1, v/v).

A 150 µl sample extract was introduced into a 3 ml fluorescence

cell, followed by 150 µl of 0.12 150 µM disodium FL solution, and 2055

ml 75 mM phosphate buffer was used as a blank. Trolox (a water-soluble

α tocophenol analogue) at 2.5, 5, and 10 µM was used as a standard. The

cell was incubated at 37°C for 15 min in a water bath. The initial

fluorescence (ƒ0) was measured at the excitation wavelength of 515 nm

using an RF-540 Shimadzu spectrofluorophotometer (Shimadzu, Kyoto,

Japan). After ƒ0 was recorded, 150 µl of 320 mM AAPH reagent, as a free

radical generator, was added into a cell and mixed well using a glass rod.

Fluorescence was measured and recorded every 5 min (ƒ5, ƒ10, ƒ15, …,

ƒ20) until the fluorescence of the last reading declined by >95 % from

the first reading (~60 min). The relative Oxygen Radical Absorbance

Capacity (ORAC) values were calculated according to the method of

Wang, et al. (1996). Values are expressed as micromoles of Trolox

equivalents (TE) per gram of fresh weight.

Measurements of Total Phenolics

Total phenolics were determined calorimetrically using Folin-

Ciocalteau reagent as described by Velioglu, et al. (1998). Two hundred

milligrams of sample were extracted for 2 h with 2 ml of 50% methanol

at room temperature on an orbital shaker set at 200 rpm. The mixture was

centrifuged for 15 min, and the supernatant was decanted into 4 ml vials.

The supernatant was used for total phenolics assay. The extract (200 µl)

was mixed with 1.5 ml of Folin-Ciocalteau reagent (previously diluted

D.A. El-Rayes

8

10-fold with distilled water) and allowed to stand at room temperature for

5 min. A 1.5 ml sodium bicarbonate solution was added to the mixture.

After 90 min at 22°C, absorbance was measured at 725 nm using a UV-

1601 Shimadzu spectrophotometer. Total phenolics were quantified from

a calibration curve obtained by measuring the absorbance of known

concentrations of ferulic acid standard.

Extraction and Determination of Flavonoids

Powdered oven-dried Barhy date fruits (1g) were extracted in a

Soxhlet extractor with 100 ml ethanol for 1 hour and the extract filtered.

A known volume of extract was placed in a 10 ml volumetric flask.

Distilled water was added to make 5 ml, and 0.3 ml NaNO2 (1:20) were

added. Five minutes later, 0.3 ml AlCl3 (1:10) were added. After 6 min,

2 ml 1 mol litre−1

NaOH were added and the total was made up to 10 ml

with distilled water. The solution was mixed well again and the

absorbance was measured against a blank at 510 nm with a M8500 UV-

visible spectrophotometer (Taizhou Radio Factory) (Zhuang, et al.,

1992).

Measurement of Total Carotenoids

Total carotenoids were extracted according to the method of

Talcott and Howard (1999). Two grams of the sample were extracted

using 25 ml acetone/ethanol (1:1, v/v) with 200 mg/l butyl hydroxyl

toluene (BHT). Samples were centrifuged at 1500 g for 15 min. The

supernatant was brought to 100 ml with the extraction solvent, and

absorbance at 470 nm was measured using a UV-1601 Shimadzu

spectrophotometer. Total Carotenoids were calculated according to the

method of Gross (1991).

Statistical Analysis

Data were analyzed using a factorial design with five replicates per

treatment, using the Student-Newman-Keul’s Test. The least significant

differences were used to compare means at P ≤ 0.05 according to the

procedure outlined by Snedecor and Cochran (1980). The experiment was

carried out for two successive seasons.


Results and Discussion

Storage Period

A great deal of extension had occurred in the storage period of full

mature ‘Barhy’ date fruits stored at 0ºC under modified atmosphere

conditions (Fig. 1). Data revealed that modified atmosphere and cold

storage treatments retarded effectively ripening and senescence of ‘Barhy’

full mature dates. All CO2 enriched treatments significantly improved the

storage ability of the fruits. Evidently, elevating CO2 concentration inside

the storing containers to 20% at 0ºC resulted in extending the storage

period of the date fruits 2.8 times than those stored at the same temperature

(0ºC) under common atmosphere conditions. ‘Barhy’ fruits stored at 0ºC

under common atmosphere conditions were discarded totally after two

months. On the contrary, fruits stored under modified atmosphere

containing 20% CO2 at 0ºC maintained their quality and showed longer

storage ability achieving 173 days.

Fig. 1. Effect of different storage temperatures and CO2 concentrations on storage ability of

Barhy date fruits.

Each value in the figure is a mean of five replicates, and three measurements were conducted for each

replicate. Means followed by the same letter, within a curve line are not significantly different (p ≥ 0.05). The

least significant differences at P ≤ 0.05 were: Storage temperature: 8.213, carbon dioxide concentration:

12.571, and the interaction: 13.875.

D.A. El-Rayes

10

Longest storage period occurred when date fruits were stored at 0ºC

under MA containing 20% CO2, followed by those containing 10% and

5% CO2, respectively. On the contrary, shortest storage period was

observed in fruits stored at 6ºC under common air atmosphere. A clear

relationship was observed between CO2 concentration inside the storing

containers and the storage ability of the fruits. The higher the CO2

concentration, the longer the storage period.

Elevated carbon dioxide during storage delays fruit ripening and

reduces respiration rate of the fruits, which extends storage life and

maintains quality. The use of elevated CO2 at storage atmosphere for

preserving fruit quality, reducing respiration rate of the fruits, and

delaying fruit deterioration has been described (Al-Redhaiman, 2005;

Attia, et al.,1997; El-Rayes and Ahmed, 2001; and Kader, 2002).

Soluble Solid Content

The percentage of soluble solids content in Barhy date fruits was not

affected significantly by CO2 or cold storage treatments (Fig. 2).

Fig. 2. Percentage of soluble solid contents in Barhy date fruits stored at different storage

temperatures under different carbon dioxide concentrations.

The least significant differences at P ≤ 0.05 were: Storage temperature 0.387, carbon dioxide concentration

0.422, and the Interaction 0.498.

Perhaps because ripening processes after "Bisr" stage of fruit

development have only a slightly effect on SSC%. A slight increase in

SSC% occurred in most treatments under investigation. This increase

could be due to the conversion of some insoluble compounds into soluble

compounds (such as the conversion of protopectin into pectin), or as

10

15

20

25

30

35

0 2 4 6

Storage temperature ( º C)

Perc

enta

ge o

f so

luble

soli

d c

onte

nts

0.03% carbon dioxide

5 % carbon dioxide

10 % carbon dioxide

20 % carbon dioxide


a result of the water loss from the fruits. Lower moisture contents could

affect SSC% positively as shown by Thompson and Abboodi (2003).

Total Tannin Contents

Both modified atmosphere conditions and cold storage temperature

affected tannin content in Barhy date fruits during storage (Fig. 3). Fruit

total tannin contents showed an inversely proportional values to the

storage period. At the end of the experiment, lowest fruit tannin content

values were observed in fruits stored at 6ºC under common atmosphere

conditions. Data indicated that fruit total tannin contents were closely

associated with fruit ripening process during the storage period, the more

advanced stage of ripening, the lower the fruit tannin content.

00 2 4 6

0.03% CO2

5% CO2

10% CO2

20% CO20.5

1

1.5

2

2.5

3

3.5

4

4.5

5

Storage temperature (°C)

Tota

l tan

nin

cont

ents

(µ m

ol.g

.-1)

Fig. 3. Total tannins contents (μ mol.g–1) in Barhy date fruits stored at different storage

temperatures under different carbon dioxide concentrations.

The least significant differences at P ≤ 0.05 were: for storage temperature 0.251, for carbon dioxide

concentration 0.232, and for the interaction 0.311.

Tannin contents of date fruits were at maximum concentration in the

Khalal (Bisr) stage (full mature stage of development) and gradually

decreased to reach a minimum concentration in the ripe stage (Rutab)

(Sawaya and Mashadi, 1983). At the beginning of the experiment, Barhy’

date fruits in the Khalal stage contained 4.2% tannins on dry weight basis

(Fig. 3). However, at the end of the experiment total tannins in fruits

stored at 6ºC under common atmosphere conditions decreased

significantly recording only 2.8%. No significant changes in tannin

content occurred in MA treated fruits supplied with 20% CO2 and stored

D.A. El-Rayes

12

at 0ºC. Moreover, fruit tannin contents showed directly proportional

values to CO2 concentration and cold storage temperature. Fruits stored at

MA and supplied with 20% CO2 at 0ºC contained the highest fruit tannin

contents compared to all other treatments and maintained, after 173 days

of storage, almost the same tannin values as it was at the beginning of the

experiment. This clearly indicates the positive effect of CO2 and cold

temperature treatments in retarding the fruit ripening process and

subsequently maintaining tannin contents. These findings are in harmony

with those of Rouhani and Bassiri, 1976 and Sawaya & Mashadi, 1983.

Total Sugar Contents

Neither modified atmosphere conditions nor cold storage temperature

treatments had any significant effect on total sugar contents of ‘Barhy’

date fruits. At the beginning of the experiment, total sugar content was

75.29% on a dry weight basis (Table 1). Evidently, at the end of the

storage period, a slight increase was observed in fruit total sugar content.

This increment occurred in all treatments under study but with different

rates. Highest rate of total sugar increment during storage period

occurred in fruits stored under common air atmosphere at 6ºC. On the

contrary, lowest rate of total sugar increment was observed in fruits

stored under MA with 20% CO2 at 0ºC. A clear relationship was

observed between fruit stage of development and total sugar content. The

more advanced stage of fruit development and ripening, the higher the

sugar content. In general, there was a slight increase in fruit total sugar

content as the fruits passed from the Khalal to Rutab (full ripen fruits)

stage. These findings are similar to those reported earlier by other

workers on various date cultivars (Coggins and Knapp, 1969; and

Sawaya & Mashadi, 1983).

Fruit Peel Color Analysis

Fruit peel color analysis indicated that both modified atmosphere

conditions and cold storage treatments influenced significantly fruit peel

lightness (L* values), the locus relative to purplish-red-bluish-green (a*

values), the locus relative to yellow-blue (b* values), the index analogous

to color intensity (c* values), and hue angle (h* values) (Tables 2-6 and

Fig. 4&5). A clear relationship was observed between CO2 concentration

inside the storing containers and the fruit peel color analysis parameters.


Fruit peel L*, a*, b*, c*, and h* values showed directly proportional

values to CO2 concentration and cold storage temperature.

Table 1. Changes in the percentage of total sugar contents in Barhy date fruits stored at

different storage temperatures under different carbon dioxide concentrations.

Each value in the table is the mean of five replicates, and three measurements were conducted for each

replicate. Means followed by the same letter, within a column are not significantly different (p ≥ 0.05) and

means followed by the same letter, within a row are not significantly different (p ≥ 0.05). LSD at 0.05 for the

interaction: NS.

Table 2. Effect of storage temperature and carbon dioxide concentrations on L* values

(lightness) of Barhy date fruit peel color. At the beginning of the experiment, fruits

were at Khalal stage, but they varied at the evaluation time between Khalal and

Rutab stages.




interaction: 4.261.

Carbon dioxide concentration Storage

temperature

(°C )

Total sugar

contents at

zero time 0.03% 5.0% 10.0% 20.0% Average

0ºC 75.6 74.9 74.8 74.3 74.9a

2ºC 77.4 77.7 75.8 75.2 76.5a

4ºC 78.2 77.8 76.7 76.1 77.2a

6ºC

74.1

79.6 78.4 78.7 77.8 78.6a

Average 77.7a 77.2a 76.5a 75.9a


temperature

(C )

Fruit color

at

zero time 0.03% 5.0% 10.0% 20.0%

Average

0ºC 37.7 40.7 41.5 65.7 46.4a

2ºC 32.7 35.1 34.1 63.8 41.4b

4ºC 31.3 33.5 33.8 43.5 35.5c

6ºC

67.1

29.4 31.6 33.1 36.4 32.6c

Average 32.8c 35.2b 35.6b 52.4a

D.A. El-Rayes

14

Fruits stored at MA and supplied with 20% CO2 at 0°C showed the

nearest values to yellow color b* compared to all other treatments. In

Barhy date fruits, decrease of fruit peel L* values in peel color is

associated with fruit ripening processes. Subsequently, the effect of both

MA conditions (at 20% CO2) and cold storage (at 0°C) on retarding the

ripening process resulted in maintaining the fruit peel lightness (L*) and

yellow color (b*) the closest to the fruit peel color at time zero.

Table 3. Effect of storage temperature and carbon dioxide concentrations on a* values (the

locus relative to purplish-red-bluish-green) of Barhy date fruit peel color.



means followed by the same letter, within a row are not significantly different (p ≥ 0.05). LSD at 0.05 (p ≥

0.05) for the interaction: 0.461.

Table 4. Effect of storage temperature and carbon dioxide concentrations on b* values (the

locus relative to yellow-blue) of Barhy date fruit peel color.




interaction: 2.151.


temperature

(ºC )

Fruit color

at

zero time 0.03% 5.0% 10.0% 20.0%

Average

0°C 2.1 3.6 4.1 4.5 3.6a

2ºC 1.8 2.9 3.0 4.3 3.0b

4ºC 1.5 2.1 2.4 2.3 2.1c

6ºC

4.7

1.3 1.4 1.8 1.8 1.6d

Average 1.7d 2.5b 2.1c 3.2a


temperature

(ºC )

Fruit color

at

zero time 0.03% 5.0% 10.0% 20.0%

Average

0ºC 16.9 18.9 22.8 27.2 21.5a

2ºC 13.2 15.5

16..2 27.5 18.8b

4ºC 8.4 12.7 15.7 18.0 13.7c

6ºC

28.2

5.1 7.3 9.5 12.8 8.7d

Average 10.9d 13.6c 16.0b 21.3a


Table 5. Effect of storage temperature and carbon dioxide concentrations on C* values (an

index analogous to color intensity) of Barhy date fruit peel color.




interaction: 2.475.

Table 6. Effect of storage temperature and carbon dioxide concentrations on h* values (hue

angle1) of Barhy date fruit peel color.




interaction: 7.562 1

hue angle is the angle between the hypotenuse and 0º on the a* (the locus relative to purplish-red-bluish-

green) axis.

Fig. 4. Storing Barhy date fruits at full mature stage (Bisr) under high CO2 concentrations

(higher than 30% CO2) could result in CO2 injury as shown above (data are not

reported).


temperature

(ºC )

Fruit color

at


0ºC 18.2 22.5 23.2 26.6 22.6a

2ºC 16.6 26.6 21.6 25.6 22.6a

4ºC 4.5 6.5 7.2 21.6 10.0b

6ºC

27.2 2.3 2.7 3.5 5.8 3.6c

Average 10.4c 14.6b 13.9b 19.9a


temperature

(ºC )

Fruit color

at


0ºC 79.9 79.9 79.5 78.5 79.5a

2ºC 31.3 52.7 61.2 59.6 51.2b

4ºC 26.9 27.9 33.8 49.5 34.5c

6ºC

80.5 24.9 26.5 30.7 38.4 30.1c

Average 40.8c 46.8b 51.3ab 56.5a

D.A. El-Rayes

16

Fig. 5. The color change during the different stages of Barhy fruit development.

Antioxidants and Phenolics Extraction Method

Data in Table 7 compares the effect of extraction methods on

antioxidant activity and content of total phenolics in Barhy date fruits

using four different solvents. Significant (p ≤ 0.05) differences existed

among different solvent used. Extraction into phosphate buffer (75 mM,

pH 7.4) gave the highest antioxidant activity (7986 µmol of TE/g),

whereas ethanol afforded the (5832 µmol of TE/g) among the solvents

used. These results suggest that most of the antioxidants in date fruits are

water soluble (hydrophilic). In contrast to antioxidant activity, ethanol/

water (50: 50, v/v) yielded the highest recovery of total phenolics (284

mg of FAE/100g). This could be due to the solubility differences of

phenolic acid in ethanol, water, or their mixture. Thus, phosphate buffer

for antioxidant activity and ethanol/ water (50: 50, v/v) for total

phenolics was selected to extract the remaining treatments.

Table 7. Comparison of extraction solvents for the contents of antioxidant activity (µ mol of

TE/g fresh) and total phenolics in Barhy date fruita.

a

Data are expressed as mean + SD on fresh weight basis. Each value in the table is the mean of five replicates,

and three measurements were conducted for each replicate. Means + SD followed by the same letter, within a

column are not significantly different (p ≥ 0.05) . b

Antioxidant activity expressed as micromoles of Trolox equivalents (TE) per gram fresh weight. c

Total phenolics are expressed as milligrams of ferulic acid equivalents (mg of FAE/100g).

Extraction solvent Antioxidant activityb

(µ mol of TE/g) Total phenolics

c

(mg of FAE/100g)

Water 7338 + 628e 226 + 7 g

Phosphate buffer (75 mM, pH 7.4) 7986 + 614d 232 + 8 f

Ethanol :Water(1:1) 6678 + 523f 284 + 11d

Ethanol 5832 + 533g 251 + 9 e


Total Phenolics

Significant differences (p ≤ 0.05) in total phenolic values were

observed among Barhy date fruits stored under different modified

atmosphere and cold storage treatments (Table 8).

Table 8. Contents of total phenolics (mg.100 g–1 dry weight) in Barhy date fruits as affected

by storage temperature and carbon dioxide concentrationsa.

a


replicate. Means followed by the same letter, within a column or a row are not significantly different (p ≥

0.05). b

Total phenolics expressed as micromoles of ferulic acid equivalents (FAE) per 100 grams of fresh weight.

The higher total phenolic values were observed in fruits at the

beginning of the experiment (at zero time before any storage treatment).

However, at the end of the experiment, no significant differences (p ≤ 0.05)

were observed between fruits stored at 0ºC under 20.0% CO2 for 173 days

and fruits at zero time regarding total phenolic values. Carbon dioxide

treatment at 20.0% maintained fruit contents of total phenolic values

significantly higher than all other CO2 treatments. Moreover, low storage

temperature (0ºC and 2ºC) maintained fruit contents of total phenolic

values significantly higher than all other cold storage treatments used in

this study. During the fruit development, the conversion of Barhy date

fruits from full mature stage to ripening stage caused a significant loss in

total phenolics (Table 8). This loss could be due to the decomposition of

natural phenolics in dates during ripening processes. The reduction in total

phenolic values during the conversion from full mature stage to ripening

stage of development has also been reported for other fruits.

Larrauri, et al., 1997, reported decreases in the total phenolic values

of red grape at high temperature during and after ripening processes.


temperature

(ºC )

Total

phenolicsb

at zero time 0.03% 5.0% 10.0% 20.0% Average

0ºC 18.7 19.4 19.5 20.8 19.6 a

2ºC 18.4 18.8 19.1 20.5 19.2 a

4ºC 14.7 16.8 17.5 19.4 17.1 b

6ºC 12.9 13.9 14.0 16.8 14.4 c

Average

21.62

16.2 b 17.2b 17.5b 19.4 a

D.A. El-Rayes

18

Contents of Flavonoids and Caroteinoids

Barhy date fruits contents of both flavonoids and caroteinoids did

not show any significant difference among different treatments stored

under different modified atmosphere and cold storage conditions (Table

9). Although a slight increase was observed in both flavonoids and

caroteinoids contents in Barhy date fruits during the storage period

compared with their values at zero time (fruits were at full mature stage

of development), however, this increment did not reach the level of

significance between the different treatments.

Table 9. Contents of total flavonoids (mg.100 g–1 dry weight) and total carotenoids (mg.100

g–1 dry weight) in Barhy date fruit as affected by storage temperature and carbon

dioxide concentrations.


replicate. Means followed by the same letter, within a column of each character are not significantly different

(p ≥ 0.05) and means followed by the same letter, within a row of each character are not significantly different

(p ≥ 0.05). LSD at 0.05 for the interaction: NS.

The lowest values of fruit contents of both flavonoids and

caroteinoids were observed in fruits at the beginning of the experiment

(at zero time before any storage treatment). In contrast, the highest values

of fruit contents of both flavonoids and caroteinoids were observed in

fruits stored at 6ºC in ambient air composition (0.03% CO2). This

increment in the values of fruit contents of both flavonoids and


temperature

Total

flavonoids

at zero time 0.03% 5.0% 10.0% 20.0% Average

Total flavonoids (mg.100 g–1 dry weight)

0ºC 2.51 2.45 2.45 2.43 2.46a

2ºC 2.58 2.56 2.52 2.49 2.54a

4ºC 2.61 2.61 2.59 2.51 2.58a

6ºC 2.64 2.62 2.61 2.55 2.62a

Average

2.38

2.59a 2.56a 2.55a 2.50a

Total carotenoids (mg.100 g–1 dry weight)

0ºC 5.83 5.79 5.72 5.67 5.75a

2ºC 6.08 5.74 5.71 5.63 5.79a

4ºC 6.15 6.04 6.11 5.81 6.03a

6ºC 6.21 6.15 6.19 6.18 6.18a

Average

5.58

6.07a 5.93a 5.94a 5.82a


caroteinoids was proportionally associated with the ripening processes

occurring in the fruits. The closer the fruit to the full ripe stage the higher

the content of both flavonoids and caroteinoids .Subsequently, the effect

of both MA conditions (at 20% CO2) and cold storage (at 0ºC) on

retarding the ripening process resulted in maintaining the fruit contents of

both flavonoids and caroteinoids closest to their values at time zero.

Conclusion

Modified atmosphere conditions maintained fruit skin color, and

overall quality parameters of date fruits. Fruits stored under MA with

high CO2 concentrations (20% CO2) looked exactly as the freshly

harvested fruits. A positive proportional relationship between CO2

concentration and both fruit quality and storage ability was recorded. The

effect of both MA conditions (at 20% CO2) and cold storage (at 0ºC) on

retarding the ripening process resulted in maintaining the fruit contents of

total phenolic, flavonoids, and caroteinoids values closest to their values

at time zero. Fruits stored under low temperature conditions (0°C) or

relatively high CO2 concentration (20% CO2) did not show any chilling

or CO2 injury symptoms. In this respect, a modified atmosphere system

could be developed for ‘Barhy’ full mature date fruits that can effectively

retard ripening and senescence, and allow shipping of the fruit to distant

markets with acceptable quality.

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