Scholarly article on topic 'Chemical quality and nutrient composition of strawberry fruits treated by γ-irradiation'

Chemical quality and nutrient composition of strawberry fruits treated by γ-irradiation Academic research paper on "Agriculture, forestry, and fisheries"

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Abstract of research paper on Agriculture, forestry, and fisheries, author of scientific article — Rabab W. Maraei, Khaled M. Elsawy

Abstract Postharvest quality losses of fruits and vegetables during storage are global horticultural problems. This study evaluates the effect of gamma irradiation doses (0, 300, 600 and 900 Gy) on quality parameters and phytochemical content of strawberry fruits during storage periods at 10 °C. The data revealed the irradiation significantly reduced the fruits weight loss and decay rate at storage periods; in comparison with control (unirradiated sample) which gave the maximum value of these quality parameters. Neither radiation treatment nor storage period had significant effect on titratable acidity and pH of fruits. All treatments decreased vitamin C levels during storage but the anthocyanin contents increased gradually during the storage period and reached its highest values near the end of the storage period. Strawberry fruits treated with 600 Gy had the highest total phenolic content and antioxidant activity followed by 300 Gy. Irradiation stimulated the biosynthesis of some phenolic compounds such as, pyrogallol, gallic, catechol, chlorogenic and ellagic acid.

Academic research paper on topic "Chemical quality and nutrient composition of strawberry fruits treated by γ-irradiation"

Journal of Radiation Research and Applied Sciences xxx (2017) 1—8

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ELSEVIER

Journal of Radiation Research and Applied Sciences

journal homepage: http://www.elsevier.com/locate/jrras

Chemical quality and nutrient composition of strawberry fruits treated by g-irradiation

Rabab W. Maraei a' *, Khaled M. Elsawy b

a Natural Products Department, National Center for Radiation Research and Technology, Atomic Energy Authority, P.O. Box 29, Nasr City, Cairo, Egypt b Regional Center for Food and Feed, Agricultural Research Center, Giza, Egypt

ARTICLE INFO

ABSTRACT

Article history: Postharvest quality losses of fruits and vegetables during storage are global horticultural problems. This

Received 29 N°vember 2016 study evaluates the effect of gamma irradiation doses (0, 300, 600 and 900 Gy) on quality parameters and

Received in re^ed form phytochemical content of strawberry fruits during storage periods at 10 °C. The data revealed the irra-

26 Deremto .2016 diation significantly reduced the fruits weight loss and decay rate at storage periods; in comparison with

Accepted 26 December 2016 j , ,■ , , ■ , , ,■ ■ ,

Available online xxx control (unirradiated sample) which gave the maximum value or these quality parameters. Neither radiation treatment nor storage period had significant effect on titratable acidity and pH of fruits. All

Keywords' treatments decreased vitamin C levels during storage but the anthocyanin contents increased gradually

Gamma irradiation during the storage period and reached its highest values near the end of the storage period. Strawberry

Phytochemical content fruits treated with 600 Gy had the highest total phenolic content and antioxidant activity followed by

Postharvest 300 Gy. Irradiation stimulated the biosynthesis of some phenolic compounds such as, pyrogallol, gallic,

Quality parameters catechol, chlorogenic and ellagic acid.

Storage © 2016 The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier

Strawberry B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/

by-nc-nd/4.0/).

1. Introduction

Strawberry fruits (Fragaria x ananassa) in family Rosaceae is an important and widely consumed fruit. The fruit is highly perishable with a shelf life of 2—3 days at room temperature and is vulnerable to postharvest decay due to its high respiration rate, environmental stresses and pathogenic attacks (Zhang, Xiao, Peng, & Salokhe, 2003). In fact, postharvest decay of fruits and vegetables triggered by inappropriate storage conditions, pathogenic attacks, mechanical injuries and environmental stresses. These factors are serious problems causing substantial losses of fresh produce every year (Zhang, Li, & Liu, 2011). Losses are generally greater in the developing countries due to their lack of experience in handling such losses and the unavailability of postharvest storage facilities as compared to the developed countries (Jeffries & Jeger, 1990).

To reduce postharvest losses and extend shelf life of fresh produce, different postharvest management techniques such as low

* Corresponding author. Scientific Divisions Building — 5th floor, 3 Ahmed ElZomor St., P.O. Box 29, Nasr City, Cairo, Egypt.

E-mail address: alrahman_27israa@yahoo.com (R.W. Maraei). Peer review under responsibility of The Egyptian Society of Radiation Sciences and Applications.

temperature storage, control atmosphere packaging and surface treatment with synthetic chemicals have been widely practiced. Controlled atmosphere packaging and low temperature storage techniques are effective and popular strategies for shelf life extension of fresh commodities however, in many reports it has been documented that these methods may not be able to control certain pathogenic fungi and bacteria in the prevailing storage conditions. Gamma irradiation has been successfully used as an alternative treatment for microbial disinfection and longevity of shelf life of fresh produce (Prakash, Inthajak, Huibregtse, Caporaso, & Foley, 2000).

Strawberry fruits are rich in natural antioxidants, including anthocyanins, flavonoids and phenolic compounds (Erkan, Wang, & Wang, 2008), which might provide human health properties. International Atomic Energy Association has recommended doses up to 3 kGy of gamma irradiation associated with low temperature storage (1—5 °C) for extending shelf life and for delaying the growth of grey mould (Botrytis cinerea) and Rhizopus rot on strawberries and fresh produce (IAEA, 1994, p. 779). Vitamin C is one of the most important free radical scavengers in plants, animals, and humans. The content of vitamin C in fruits and vegetables depends on various factors such as genotypic differences, preharvest climactic conditions, and postharvest handling procedures (Lee & Kader,

http://dx.doi.org/10.1016/j.jrras.2016.12.004

1687-8507/© 2016 The Egyptian Society of Radiation Sciences and Applications. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

2000). Flavonoids are widely distributed bioactive compounds found in plant foods and can be grouped in several structural classes including anthocyanins, flavones, flavan-3-ols, flavanones, flavonols, and tannins. Besides being closely associated with the sensory attributes of fruits, flavonoids and phenolic acids have received increased attention due to their potential antioxidant activities, which may also exert cardio protective effects in humans. Strawberries were recently reported as having the highest antiox-idant activity among 12 fruits analyzed, and the contribution of vitamin C to the total antioxidant activity was estimated as being <15% (Wang, Cao, & Prior, 1996). The amount of anthocyanins is important for the maturity evaluation of strawberries. The index of maturity used for harvesting is the red color resulting from anthocyanin synthesis corresponding to half or three-fourths of the fruit. The main anthocyanin found in strawberries is pelargonidin 3-glucoside, with cyanidin 3-glucoside and pelargonidin 3-rutinoside present as minor components.

The aim of this work was to investigate the effect of different doses of gamma rays on quality and chemical composition of strawberry fruits during storage periods.

2. Materials and methods

Fruits of freshly harvested at 3/4 red color stage from strawberry (Fragaria x ananassa cv. Festival) were collected from farm located at Qalyubia Governorate. Fruits of uniform size without any defect were packed in plastic punnets (250 g) and placed in carton boxes. The fruit samples were subjected to gamma irradiation doses (0, 300, 600 and 900 Gy) using 60Co with a dose rate of 1.9 kGy/h at the National Center for Radiation Research and Technology, Atomic Energy Authority, Nasr City, Cairo, Egypt. The irradiated and unirradiated samples were stored for 9 days at 10 °C during January. The following parameters were evaluated on day 0, 3, 6, and 9 after storage.

2.1. Weight loss %

Weight loss % was calculated by the following formula as described by Akhtar, Abbasi, and Hussain (2010).

Weight loss % = [(a-b)/a] x 100, where a and b represent initial and final fruit weights, respectively.

2.2. Decay %

Decay % was calculated by visual observation of each sample as described by Zheng, Wang, Wang, and Zheng (2007). A fruit with visible brown spot and softened area was regarded as decayed and results were expressed as percentage of decayed fruits.

2.3. Determination of pH and titratable acidity

Determination of pH and titratable acidity, 5 fruits were randomly taken from each treatment and blended in an electrical blender, then filtered to obtain clear juice of homogenate. Titratable acidity was calculated by titrating 10 ml of clear juice of strawberry diluted in 100 ml of deionized water against 0.1 N NaOH solution (AOAC, 1995) and the results were expressed as citric acid %. pH of the samples was measured by a digital pH meter. All evaluations were carried out four times during study i.e., at day 0, 3, 6 and 9 after storage at 10 °C.

2.4. Ascorbic acid content

Ascorbic acid content was determined by using 2,6-dichlorophenol indophenols titration method as described by

AOAC (2000).

2.5. Anthocyanin content

Anthocyanin content was determined colorimetrically. Results were expressed as mg cyanidin-3-O-glucoside g-1 fresh weight where the molecular weight of cyanidin-3-O-glucoside = 449.2 g mol-1 and the molar extinction coefficient = 26 900 1 mol-1 cm-1 (AOAC, 2000).

2.6. Total phenolic contents

Total phenolic contents, strawberry samples were extracted and determined according to the methods described by Toor and Savage (2005). Total phenolic contents were determined with spectro-photometer using Folin-Ciocalteu reagent and the results were expressed as gallic acid equivalents, in mg g-1 fresh weight.

2.7. DPPH radical scavenging activity assay

DPPH radical scavenging activity assay was based on the method described by Odriozola-Serrano, Soliva-Fortuny, and Martm-Bel-loso (2008). The absorption of the sample at 515 nm was measured by a spectrophotometer. Results were expressed as percentage of inhibition of the DPPH radical (antioxidant activity %).

2.8. HPLC analysis for phenolic compounds

HPLC analysis for phenolic compounds, The identification on the phenolic compounds from fruits extract were performed by HPLC according to Christine, John, and Jane (1999) in Food Technology Institute, Agricultural Research Center, Giza-Egypt. HPLC was equipped with a Hewlett- Packard 1050 photodiode array detector (Agilent Technologies, Palo Alto, Calif., U.S.A) with Hewlett- Packard HPLC ChemStation software and autosampler, using a PDS-column C18, 5 mm (150 mm x 4.6 mm, operated at 45 °C. The solvent system used was gradient of A (acetic 2.5%), B (acetic 8%) and C (acetoni-trile). The solvent flow rate was 1.0 ml/min and the injection volume was 50 ml. Phenolic compounds were calculated by external standard calibration at 280 nm.

2.9. Statistical analysis

The experiment was conducted in a randomized complete block design (RCBD) manner. Three replicates per treatment were evaluated. Data was statistically analyzed by analysis of variance (ANOVA) technique and the means were separated by Duncan (1955) Multiple Range test. All statistical tests were performed at a 5% significance level.

3. Results

3.1. Weight loss %

Effect of storage intervals and radiation doses (especially higher doses) have significant effects on weight loss of fruit. Weight loss at 3, 6 and 9th day of storage varied considerably. Maximum weight loss occurred in control and 300 Gy at 9th day of storage, which accounted 49.88 and 45.55% loss, respectively (Fig. 1). Conversely, radiation doses 600 and 900 Gy significantly reduced weight loss at different storage periods. Compared to control, weight loss in fruit samples treated with 600 and 900 Gy was 37.26 and 28.91% at the 9th day of storage period.

Days after storage

Fig. 1. Effect of different doses of gamma irradiation on weight loss % of strawberry fruits at different storage periods. Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant differences at P < 0.05.

3.2. Decay %

Radiation treatment and storage period significantly altered fruits decay %. Decay was greater in control, virtually in every assessment of storage interval than radiation treatments (except 300 Gy). In control samples, 16.67, 63.33 and 86.7% fruits rotted followed by 13.33, 60 and 83.33% decayed fruits treated with 300 Gy at 3, 6 and 9th day of storage, respectively. Increase in radiation dose to 600 and 900 Gy slowed down the decay. At these two levels of doses, percentage of decayed fruits significantly reduced at different storage days. At 9th day of storage, 73.33% fruits were recorded as decayed from samples treated with 600 Gy when compared to control (86.7%). Radiation dose 900 Gy proved effective in controlling fruit decay where only 36.7% fruits rotted (Fig. 2).

3.3. pH and titratable acidity

pH and titratable acidity (TA) of control and irradiated fruits did not change significantly during storage period. Control and irradiated fruit samples showed almost consistent values of pH and TA at different storage intervals (Figs. 3 and 4). Irradiated samples

showed similar pH values which did not differ significantly from control. Almost similar results were recorded for other treatment at different storage intervals. Results showed that TA of control and irradiated fruits remained unchanged at different storage periods. TA values of strawberry varied between 0.504 and 0.520% at different treatments and storage intervals, which revealed no significant differences. These obtained results are in agreement with those mentioned by Majeed, Muhammad, Majid, Shah, and Hussain (2014), who indicated that gamma irradiation doses up to 1.5 kGy may be effectively used for shelf life extension and for minimizing postharvest decay and weight loss of strawberry without causing drastic changes in its pH, and TA.

3.4. Ascorbic acid (vitamin C) content

In strawberry, vitamin C content was significantly affected by original content or the variety rather than treatments such as irradiation, heating or microwave. These results indicated that the losses of water soluble vitamins, especially thiamin or vitamin C, were affected by the food temperature during the irradiation process (Chung & Yook, 2003).

The data recorded in Fig. 5 shows L-ascorbic acid (Vitamin C)

Days after storage

Fig. 2. Effect of different doses of gamma irradiation on decay % of strawberry fruits at different storage periods. Vertical bars show standard deviation (n = 3). Different letters indicate statistically significant differences at P < 0.05.

Days after storage

Fig. 3. Effect of different doses of gamma irradiation on pH values of strawberry fruits at different storage periods.

- storage

Fig. 4. Effect of different doses of gamma irradiation on acidity % of strawberry fruits at different storage periods.

content (mg/100 g FW). All doses caused non-significant decrease of vitamin C content during storage except for the dose of 900 Gy which caused significant decrease in vitamin C content and a gradual decrease of vitamin C content is occurred with the increase of storage time were observed in all treatments. Similar observations were reported by Maxie, Sommer, and Rae (1964). They reported that non-significant decrease in vitamin C levels when submitted to 1.0—2.0 kGy doses, during 2 and 11 days of storage at 5 °C in Strawberries (Shasta variety, Fragaria sp.).

3.5. Anthocyanin content

The color of strawberry depends chiefly on the presence of water soluble anthocyanin pigments and among them pelargoni-dine-3-monoglucoside. Degradation of anthocyanins by irradiation was greatest in purified pigments, followed by fruit juices, and the least in whole berries (IAEA, 1994, p. 779).

Amongst strawberry, red current and raspberry fruit

exposed to doses in the range of 1.5—7.5 kGy, the least degradation of pigments occurred in strawberry. In strawberries exposed to 2.5 kGy, a dose destroyed 20% anthocyanins, total regeneration of pigments was noted during 6 days storage; however fruits exposed to higher doses did not show regeneration, possibly due to irreversible changes in the anthocyanin molecule.

The results (Fig. 6) revealed that the anthocyanin contents increased gradually during the storage period and reached its highest values near the end of the storage period. Untreated fruits had the highest anthocyanin content followed by 300, 600 and 900 Gy, respectively. These result agree with Ayala-Zavalaa, Wang, Wanga, and Gonzalez-Aguilarc (2004) who found that anthocyanin content decreased in strawberry fruit stored at 0 °C and 5 °C during the first 5 days. Meanwhile, anthocyanin content in fruit stored at 10 °C increased gradually during the storage period and reported that total anthocyanin content was significantly affected by the temperature and storage period.

Fig. 5. Effect of different doses of gamma irradiation on ascorbic acid content (mg/100 g FW) of strawberry fruits at different storage periods.

Fig. 6. Effect of different doses of gamma irradiation on anthocyanin content (mg/g FW) of strawberry fruits at different storage periods.

Fig. 7. Effect of different doses of gamma irradiation on phenolic content (mg/g FW) of strawberry fruits at different storage periods.

3.6. Total phenolic content

Total phenolic content is shown in Fig. 7. Strawberry fruits treated with 600 Gy had the highest total phenolic content followed by 300 Gy. Control fruit had the lowest total phenolic content. Total phenolic content was increased during 9 days storage period in all treatments. However, this increase was relatively lower in control fruit when compared to irradiated fruit. Such changes in the phenolic compounds in irradiated fruits may be attributed to the effect of gamma radiation on the phenolic biosynthesis and the related oxidative enzymes. These results are in concomitant with those reported by Erkan et al. (2008) on strawberry.

3.7. Antioxidant activity %

Antioxidant activity % in strawberry fruits in all treatments increased during 9 days storage at 10 °C (Fig. 8). However, this increase was relatively lower in control fruit when compared to treated fruits. Strawberry fruits treated with 600 Gy and stored for 9 days have the highest antioxidant activity (84.03%) followed by 300 Gy (82.43%) and 900 Gy (81.45%) gamma irradiation. Control fruit had the lowest antioxidant activity which was 80.08%.

3.8. HPLC analysis for phenolic compounds

Fruits and vegetables consumption is important because they prevent the occurrence of the chronic diseases, including type 2 diabetes. This is due to the abundance in composition of fiber, an-tioxidants, and other bioactive compounds with beneficial health effects (Muraki et al., 2013). With regard to the fruits, they represent a valuable source of polyphenols which contribute to the nutritive quality, and also giving some organoleptic properties. Their composition differs from one cultivar to another, also being influenced by biotic and abiotic factors (Tudor, Manole, Teodorescu, Asanica, & Barbulescu, 2015). Therefore, in this study we looked at how the different doses of gamma rays and storage period influenced the phenolic compounds in strawberry fruits.

Data presented in Tables 1 and 2 show the contents of phenolic compounds after irradiation immediately and after 9 days from storage, respectively.

Irradiation stimulated the biosynthesis of some phenolic compounds such as, pyrogallol, gallic, catechol, chlorogenic and ellagic acid. Meanwhile, ethyl vanillate appeared in the irradiated treatments only (600 and 900 Gy) after irradiation immediately. These

Table 1

Effect of different doses of gamma irradiation on phenolic compounds profile (ppm) of strawberry fruits after irradiation immediately.

Phenolic compound Irradiation dose (Gy)

0 300 600 900

Pyrogallol 165.82 373.01 269.82 203.16

Gallic 8.45 11.15 14.95 9.65

4-amino-benzoic 5.86 10.46 9.91 6.31

Protocatechuic 80.14 81.59 89.24 143.93

Catechin 810.69 619.88 988.82 415.10

Catechol 23.02 27.13 36.53 51.46

Chlorogenic 41.21 60.25 104.39 62.81

Epicatechin 33.23 93.04 25.46 36.97

p-OH-benzoic 111.71 141.00 113.00 125.26

Caffeine 9.24 55.31 34.0 27.34

Caffeic 11.08 13.26 13.97 10.09

Vanillic 46.45 25.99 15.45 38.26

p-coumaric 49.39 40.54 30.11 53.91

Ferulic 39.79 36.35 20.20 25.95

Iso-ferulic 50.40 43.99 31.39 37.98

Ethyl vanillate — — 47.09 60.11

Ellagic 338.58 661.89 555.37 377.45

a-coumaric 110.94 100.69 122.45 112.26

Benzoic 132.47 142.41 149.93 161.20

3,4,5-methoxy-cinnamic 15.75 20.39 13.80 26.65

Coumarin 44.63 40.96 41.34 45.02

Salicilic 180.33 155.66 191.60 130.81

Cinnamic 2.28 2.85 2.77 1.04

results are in agreement with those of Rabab (2012) on lavender. After 9 days from irradiation the phenolic compounds increased by storage such as pyrogallol, gallic, 4-amino-benzoic, protocatechuic, catechol, epicatechin, caffeine, ferulic and benzoic acid. There were some other phenolic compounds which increased in irradiated treatments than unirradiated one such as catechin, a-coumaric and salicylic acid. The results are similar to finding of Ayala-Zavalaa et al. (2004) total phenolic compounds are increasing continuously in berries during the storage period.

4. Discussion

Irradiation either alone or in conjunction with modified atmospheres extends the shelf life of strawberries further by providing control of grey mould rot and Rhizopus rot during refrigerated transport, storage, market display as well as in consumer households. During storage period of fresh produce, respiration rate and senescence process increases, which alter moisture contents of

Table 2

Effect of different doses of gamma irradiation on phenolic compounds profile (ppm) of strawberry fruits after 9 days from storage.

Phenolic compound Irradiation dose (Gy)

0 300 600 900

Pyrogallol 249.34 563.50 364.64 278.16

Gallic 10.21 17.52 15.40 10.78

4-amino-benzoic 6.71 18.14 12.42 7.80

Protocatechuic 91.83 113.20 125.24 98.24

Catechin 565.88 763.50 924.15 623.83

Catechol 62.20 33.53 39.56 58.54

Chlorogenic 30.15 56.35 71.86 53.72

Epicatechin 43.66 120.08 127.73 109.54

p-OH-benzoic 55.16 62.94 76.27 61.55

Caffeine 24.62 63.24 70.07 44.75

Caffeic 5.71 7.67 8.97 5.74

Vanillic 56.77 62.67 89.27 65.16

p-coumaric 80.91 105.35 126.37 95.56

Ferulic 50.22 43.66 82.99 36.25

Iso-ferulic 73.06 88.70 109.25 79.73

Ethyl vanillate 378.20 577.16 749.81 800.49

Ellagic 180.41 319.45 485.43 224.08

a-coumaric 93.99 112.59 120.94 102.15

Benzoic 156.46 175.82 168.85 170.66

3,4,5-methoxy-cinnamic 5.57 10.77 7.17 13.41

Coumarin 40.56 38.79 47.42 52.89

Salicilic 139.89 169.87 182.96 151.77

Cinnamic 1.49 2.29 1.56 0.90

produce and may cause weight loss (Ayranci & Tunc, 2003). Studies show that respiration rate often decreases with irradiation doses, with greater reductions at higher dose level, arguably due to reduced metabolic activities of irradiated samples (Boynton et al., 2005). Reduction in weight loss at high radiation doses in this study may possibly be due to reduced respiration rate and metabolic activity of irradiated fruits. These results are compared to findings of Hussain, Meena, Dar, and Wani (2008). They reported that radiation doses 1.2—1.4 kGy reduced weight loss and prolonged peach fruits decay from 6 to 20 days at room temperature and refrigerator respectively.

Efficacy of gamma irradiation on minimizing decay of fruits and vegetables may be associated to its ability of penetration deep into tissues and destroying spoilage microorganism harbored in wounds or inside host tissues, thus preventing or minimizing the decay process by inhibiting the growth of these microbes (Barkai-Golan, 2001, pp. 418—442). Previously, significantly reduced rotting (decay) has been reported in strawberries treated with 2.0 and 2.5 kGy, stored for two weeks and in peach (Prunuspersica) exposed to gamma irradiation doses ranging 1.0—2.0 kGy (Hussain, Meena, Dar, & Wani, 2008). It is widely accepted that physico-chemical changes of fresh produce during storage are linearly correlated to nature of fruit, senescence, respiration rate and storage environment (Lee, Arul, Lencki, & Castaigne, 1995).

Increasing the radiation dosage gradually decreased the fruits vitamin C concentration, (Wen, Chung, Chou, Lin, & Hsieh, 2006). The loss of vitamin C of fresh-cut lettuce irradiated with 1.0 kGy was significantly lower than that of non-irradiated. The best treatment of maintaining quality of the fresh-cut lettuce appeared to be 1.0 kGy irradiation (Zhang, Lu, Lu, & Bie, 2006). Ascorbic acid is one of the most sensitive vitamins to irradiation (Kilcast, 1994). Irradiation causes oxidation of ascorbic acid to dehydroascorbic acid, which is also active biologically. It can thus be concluded that at dose levels of 300 or 600 Gy there is no nutritionally significant effect of irradiation on vitamin C content.

The increase in ascorbic acid content during storage suggested additional maturation and ripening occurred during storage, resulting in a net synthesis of ascorbic acid but the decrease during

ripening would be attributed to the decomposition of ascorbic acid as the fruit underwent senescence (Bolyston, Reitmeier, Moy, Mosher, & Taladriz, 2002). Varietal differences, metabolic changes in plant tissue, and storage effects are reported to have a greater impact on ascorbic acid content of fruits than irradiation treatment (Kilcast, 1994).

Anthocyanins are largely responsible for the red color of ripe strawberries. Several reports have indicated that UV light exposure promotes anthocyanin synthesis in strawberries and sweet cherries. The increase in total phenols and anthocyanins in blueberries by UV light illumination appears to be dose dependent at lower doses (0.43-2.15 kJ m~2) (Wang, Chen, & Wang, 2009). On the other hand, Pan, Vicente, Martinez, Chaves, and Civello (2004) has reported anthocyanin accumulation was delayed by UV light illumination in strawberry fruit. Also, this phenomenon has been reported in strawberries where high doses of UV light exposure are thought to cause too much stress and possibly result in injury. Phenylalanine ammonia-lyase (PAL) activity increases after UV light irradiation (Nigro, Ippolito, Lattanzio, Di Venere, & Salerno, 2000). This enzyme plays a key role in the biosynthesis of phenolic compounds, many of which were flavonoids and anthocyanins. The differences in the effect of irradiation on total phenolic content (increase or decrease) may be due to plant type, geographical and environmental conditions, state of the samples (solid or dry), phenolic content composition, extraction solvents, extraction procedures, temperature, dose of gamma irradiation, etc. (Khattak, Simpson, & Ihsanullah, 2008). Phenolic compounds in fruits and vegetables may produce the beneficial effects by scavenging free radicals (Chun, Kim, & Lee, 2003). Thus, phenolic compounds may help protect cells against the oxidative damage caused by free radicals. In this study, total phenolic and total anthocyanin contents were variable in strawberry extracts treated with different doses of gamma rays. Strawberries stored at 10 °C for 9 days have a higher total phenolic content than strawberries stored for 3 and 6 days. This increase with the storage duration occurred in all treatments. Previous studies have shown that the amount of total phenolic content in strawberries depends on the storage temperature and atmospheric compositions (Wang & Zheng, 2001).

The main characteristics related to the quality of ripe strawberry fruits are texture, flavor and anthocyanin content. Anthocyanins are a group of phenolic compounds responsible for the red-blue color of many fruits and vegetables, and provide beneficial effects to human health (Garcia-Alonso, Rimbach, Rivas-Gonzalo, & Pascual-Teresa, 2004). The amount of anthocyanin is important for the attractiveness and maturity assessments of strawberries as well. Anthocyanin content increased in all treatments during storage period. That means the strawberries became darker with storage as ripening progresses.

Regarding the behavior of the bioactive compounds and their interaction with irradiation and storage time, many factors that can influence, such as the radiation dose, solvents used in the extraction, treatment and technological processes, during storage and mainly the characteristics of each phenolic compound and each product (Ito et al., 2016). Also, This behavior of phenolic compounds be due to the destructive processes of oxidation and gamma radiation, which are able to break the chemical bonds of polyphenols, releasing soluble phenols with low molecular weight and increasing these compounds with antioxidant action (Adamo et al., 2004).

5. Conclusion

This study showed that strawberries treated with gamma rays had higher antioxidant activity and less decay than control fruits. These results suggest that gamma rays treatments may be a useful

non-chemical way for maintaining strawberry fruit quality and extending their postharvest life.

Acknowledgments

This work was supported by the Atomic Energy Authority and Agricultural Research Center.

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