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Title: Effects of Co-60 gamma-irradiation and refrigeratedstorage on quality of Shatang mandarin
Author: Ke Zhang Yueye Deng Haohao Fu Qunfang Weng
PII: S2213-4530(14)00003-2DOI: http://dx.doi.org/doi:10.1016/j.fshw.2014.01.002Reference: FSHW 30
To appear in:
Received date: 21-10-2013Revised date: 7-1-2014Accepted date: 17-1-2014
Please cite this article as: K. Zhang, Y. Deng, H. Fu, Q. Weng, Effects of Co-60 gamma-irradiation and refrigerated storage on quality of Shatang mandarin, Food Science andHuman Wellness (2014), http://dx.doi.org/10.1016/j.fshw.2014.01.002
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Effects of Co-60 gamma-irradiation and refrigerated storage 1
on quality of Shatang mandarin 2
Ke Zhang1, Yueye Deng2, Haohao Fu2, Qunfang Weng*3
1 Key Laboratory of Pesticide and Chemical Biology, Ministry of 4
Education,Guangzhou 510642, China; Emails: [email protected] (K. Z.); 5
[email protected] (Y. D.);[email protected] (H. F.). 6
2 The authors who equally contribute this research. 7
* Author to whom correspondence should be addressed; E-Mail: [email protected]
(Q. W.); 9
Tel.: +86-20-8528-0308; Fax: +86-20-8528-0292. 10
Received: / Accepted: Published: 11
12
13
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Abstract: The effectiveness of Co-60 gamma irradiation in controlling citrus red 1
mite (Panonychus citri McGrego) had been proved in our earlier work, however,2
whether it could be used as an alternative method to replace the current way of 3
quarantine treatment against citrus red mites depends on the performances of 4
those effective doses on citrus fruits. This study was conducted to explore the5
effects of Co-60 gamma irradiation on nutrient composition of citrus (Shatang 6
mandarin), selected fruits were divided into different groups and each group were 7
irradiated at 0.0 kGy, 0.2 kGy, 0.3 kGy, 0.4 kGy, 0.5 kGy, 0.6 kGy, respectively, 8
then the treated fruits were stored at temperature of 4 � and the nutrient 9
composition were studied in the following days. The results showed that the 10
shelf-life could be extended when fruits were irradiated at a dose range of 0.2-0.411
kGy, while most unirradiated citrus decayed by 15 days. It also turned out that the 12
citrus irradiated at 0.5 and 0.6 kGy were fully decayed within 45 days of 13
refrigerated storage. Total soluble solids (TSS), total sugar, ascorbic acid (AA),14
and titrable acidity had no significant differences against control during the 15 15
days storage period. Nevertheless, the activities of peroxidase (POD) and 16
superoxide dismutase (SOD) decreased after 15 days; the improvement of storage 17
quality and shelf life may be explained by the change of the protective enzyme 18
activity. As a conclusion, the results of citrus fruit under irradiation at a certain19
dose indicating the potential use of Co-60 gamma irradiation as a safe quarantine 20
treatment.21
Keywords: Shatang mandarin; irradiation; cold storage; nutrient composition22
23
1. Introduction24
Shatang mandarin (Citrus reticulate Blanco) is a kind of characteristic fruit in25
Southeast China, mainly grows in Guangdong Province, South China. It is one of the 26
best commercial fruits of Guangdong Province. Due to the fruit tastes as sweet as 27
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sugar, it’s also called Mitangju. It is cultivated on a large area which accounts for 1
about 80% of citrus planting area in Guangdong Province, due to its reasonably higher2
yield, better quality, greater taste and flavor than those of the other citrus fruits.3
Gamma radiation has been used as a post-harvest food preservation process for 4
many years[1]. Citrus is a seasonal product, which was consumed fresh or processed. 5
Gamma irradiation emerged recently as a possible alternative technology for the citrus6
post-harvest processing, in order to fulfill the requirements of international 7
phytosanitary trade laws. The goal of quarantine or phytosanitary treatments is to 8
prevent the invasion and propagate of regulated pests [2]. Phytosanitary treatments, 9
allow for the destruction or removal of pests or for making the pest reproductively 10
sterile, to achieve the goal of control pest. There are various types of disinfestation 11
treatments including cold, hot water immersion, heated air, methyl bromide 12
fumigation and irradiation [3]. In addition, some of these techniques could help to 13
minimize the loss of quality in terms of flavor, color and nutritional value [4]. Studies 14
have showed that ‘Clemenules’ is a mandarin cultivar highly tolerant to X-ray 15
irradiation and the commercial quality of the fruit was not adversely affected by 16
postharvest quarantine applications that effectively controlled the Medfly [5]. Miller 17
found that grapefruit irradiated at 0.3 kGy resulted in minimal injury to the fruit [6]. 18
Furthermore, studies have demonstrated that ‘Rio Red’ grapefruit exposed to 19
irradiation doses of up to 0.5 kGy did not affect soluble solids, titratable acidity, 20
appearance, and organoleptic quality compared to untreated fruit[7]. Ascorbic acid is 21
water-soluble vitamin, which is present in fresh fruit, especially citrus fruit and 22
vegetable. In addition, ascorbic acid shows antioxidative effects and under certain 23
conditions can protect against oxidativlely induced DNA damage [8]. Khalil reported 24
that citrus fruits with doses of 0.25 and 0.5 kGy alone packed in cellophane bags and 25
stored at room temperature for 42 days, acidity and ascorbic acid values were higher 26
for the oranges irradiated at 0.5 kGy, weight loss decreased and total soluble solid 27
(TSS) increased during storage period[9]. Girennavar studied the influence of E-beam 28
irradiation on bioactive compounds of grapefruits, found that the acidity decreased 29
slightly with an increasing E-beam dose, whereas the total soluble solids increased 30
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and irradiation did not affect the vitamin C content at doses up to 1.0 kGy[ 10].1
Irradiation for postharvest disinfestation has been investigated for various fruits 2
and vegetables and shows great promise in that it sterilizes insects at doses that are 3
low enough not to be detrimental to most fruits and vegetables [11, 12]. The United 4
States Department of Agriculture-Animal and Plant Health Inspection Services 5
(USDA-APHIS), together with other international regulatory bodies, such as the 6
International Atomic Energy Agency (IAEA) and the International Plant Protection 7
Convention (IPPC), have issued guidelines for irradiation treatments to meet export 8
and quarantine restrictions [13].9
The benefits of using irradiation are that the cold treatment allows quality to be 10
maintained, leaves no residue on the product, and reduces the use of fumigants and 11
pallet loads can be treated at a time. Low dose gamma irradiation (1.0 kGy or less) 12
has been shown to control insect pests with little quality loss to fresh produce [14];13
however, energy is imparted into metabolically alive tissues of the commodities, so 14
undesirable damage could be occurred [15]. In 2006, the USDA-APHIS approved 15
generic treatments of 0.15 kGy for fruit flies and 0.40 kGy for all insects except pupa 16
and adult Lepidoptera [16]. However, there are few reports on irradiation quarantine 17
treatments on controlling pest mites. Similarly, the content of health-promoting 18
compounds in citrus fruit may be altered by postharvest treatments such as irradiation. 19
For instance, recent studies showed that irradiation of citrus fruit significantly reduced 20
the total ascorbic acid (TAA) content when irradiation doses were high[10, 17]. 21
However, information is still scarce on the effect of Co60-γ irradiation on nutritional 22
quality of many citrus cultivars.23
The objectives of this research were to evaluate the dose response of quality 24
factors of Shatang mandarin to irradiation at 0.2-0.6 kGy. Meanwhile, we found the 25
irradiation treatment extend the shelf life and delay fruit senescence of the citrus fruit.26
2. Materials and methods27
2.1. Fruits and Reagents28
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Shatang mandarin samples were obtained from a certain supermarket, the citrus 1
fruits were harvested in a commercial orchard in Shaoguan city, Guangdong Province. 2
The uniform size, maturity and fresh citrus were selected.3
Bovine albumin was purchased from Shanghai Fanke Biological Technology Co., 4
Ltd, Guaiacol was purchased from Tianjin Kemiou Chemical reagent Co., Ltd. SOD 5
enzyme kit was purchased from Nanjing Jiancheng Bioengineering Institute, and6
other chemicals and solvents were purchased from Guangzhou Chemical reagent 7
Factory. Water was treated in a water purification system, Unique + UV + UF, 8
Research Scientific Instruments Co., Ltd.9
2.2. Exposure to Co60γ Irradiation10
The experimental material was irradiated by Co60γ-rays at the Furui high-energy 11
Technology Co. Ltd., a Canadian company Nordion Co60γ radiation source, Nansha 12
District, Guangzhou Guangdong Province, China. The samples were divided into six 13
groups to be exposed to different radiation doses (0, 0.2, 0.3, 0.4, 0.5 and 0.6 kGy, 14
and the dose rate was 4 Gy/min, using Fricke dosimeter calibration) with 100 units 15
per group. The groups 2-6 were placed into polyethylene plastic bags and irradiated 16
with 0.2, 0.3, 0.4, 0.5 and 0.6 kGy, respectively. Group 1 was the control sample. The 17
control and the treated samples were then packed in plastic bags and stored at 4 � for 18
45 days.19
2.3. Analysis of major individual quality after Co60γ radiation20
2.3.1.Analysis of weight loss and decay rates21
Each treatment contained 10 fruits and their weight loss were tested. The 22
percentage of weight loss was calculated by following formula:23
[(Fresh weight -Weight at storage interval)/Fresh weight] ×100. 24
Similarly, the decay rate was calculated by (decayed fruits number/total tested 25
fruits number) ×100.26
2.3.2. Total sugar27
Total sugar was determined by saccharimeter (LB32T, Guangzhou Mingrui28
Electronic Technology Co., Ltd.) , measuring refractive index of fruit juices, the 29
concentration of sugar was calculated.30
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2.3.3. Titrable acidity1
1.0 mL fresh juice was added into bidistilled water of 10 mL, titrable acidity was 2
determined according to the AOAC methods[18]. 3
2.3.4. Ascorbic acid4
Ascorbic acid was determined by direct iodine titration. Each 25 ml of the herbal 5
fresh juice was transferred into a 250 ml Erlenmeyer flask. Twenty-five milliliter of 26
N sulfuric acid was added, mixed, diluted with 50 ml of water and 3 ml of starch T.S. 7
was added as an indicator. The solution was directly titrated with 0.1 N iodine 8
previously standardized with primary standard arsenic trioxide. A blank titration was 9
performed prior titration of each sample (n=5). Each ml of 0.1 N iodine is equivalent10
to 8.806 mg ascorbic acid[19].11
2.4. Analysis of protective enzyme activities12
The pulp (1.00 g) of citrus tissues with 10mL 5mM phosphate buffer (pH 7.8 or 13
pH 6.8) in a cold mortar, to grind. The seriflux was then centrifuged at 12,000×g at 4 14
℃ for 15 min. The supernatant was used as the crude enzyme extract. Peroxidase 15
(POD) activity was assayed by measuring the increase in absorbance at 470 nm using 16
4-methylcatechol as a substate prepared in a buffer solution with a pH of 6.8. The 17
reaction was carried out in a 10 mm light path quartz cell. One unit (U) of POD was 18
defined as the amount of enzyme that caused the increase of one absorbance unit (AU) 19
at 470 nm in 10 min. Superoxide dismutase (SOD) activity was assayed by SOD 20
enzyme kit. SOD activity was assessed by measuring the dismutation of superoxide 21
radical generated by xanthine oxidase and hypoxanthine, colormetric analysis. 22
2.5. Statistical analysis23
Statistical analysis was conducted for each of the measured traits by analysis of 24
variance(ANOVA) and the means were separated by Duncan Multiple Range test 25
using the SPSS software, version 18.0 (SPSS, Inc.). In addition, a linear discriminant 26
analysis (LDA) was used to assess the influence of either different storage times or 27
irradiation doses on proximate composition profiles as well as in major individual 28
quality (weight loss, decay rate, total sugar, titrable acidity, ascorbic acid and 29
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protective enzyme activities). All statistical tests were performed at a 5% significance 1
level. All the assays were carried out in triplicate. The results were expressed as mean 2
values with standard deviation (SD).3
4
3. Results and Discussion5
3.1 Physical Properties6
There were little influence on the index of Shatang mandarin when treated at the 7
dose of 0.2-0.4 kGy. The shelf life of Shatang mandarin could be prolonged by dose8
of 0.2-0.4 kGy, and only slight changes of weight losses were observed during the 9
whole experimental process. There was no significant difference between irradiated 10
citrus and the control in weight loss after 7 days, also, weight loss rates of groups 11
treated at 0.2-0.4 kGy, which was no more than 0.01%, were significantly lower than 12
the control after 15, 30 and 45 days by irradiation, respectively(Table 1.), while 13
groups treated by 0.5 and 0.6 kGy were almost decayed, indicating that the irradiation 14
treatment at 0.2-0.4 kGy could prolong the shelf life of Shatang mandarin, and the 15
high dose (0.5-0.6 kGy) would cause damage to fruit.16
Decay rates of groups treated by 0.5 kGy and 0.6 kGy reached 21% and 35% after 17
7 days of treatment, respectively (Table 2.), while, the control and the citrus treated by 18
0.2-0.4 kGy, no rotted fruit was appeared. 15 days after irradiation, 0.5 kGy and 0.619
kGy irradiated citrus decay rates were both more than 50%, while it was only 2.00% 20
and 1.67% in the control group and 0.4 kGy treated group, respectively. There were21
no decay fruit in 0.2 kGy and 0.3 kGy irradiated groups. 30 days after 22
irradiation, the decay rates of 0.5 kGy and 0.6 kGy irradiated groups were more than 23
90%, while the 0.2 kGy and 0.3 kGy treated groups still kept the lowest decay 24
rates, less than 5%, and the decay rates of 0.4kGy irradiated group was 5.3%, as 25
compared to the control 6.7%. The decay rates reached 100% after 45 days26
irradiation, with 0.5 kGy and 0.6 kGy, but they were less than 10% in 0.2 kGy and 0.327
kGy irradiated groups, and the 0.4 kGy irradiated group was lower than that of 28
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control. The irradiation dose below 0.4 kGy (including 0.4 kGy), had a preservative 1
effect on Shatang mandarin, while high doses would cause serious damage to 2
the Shatang mandarin.3
The effect of gamma irradiation on total sugar under different doses was carried 4
out in this study. The results showed that the total sugar content decreased with the 5
extension of storage time (Table 3.). There were no significant differences between 6
treated fruits and the control group in the content of total sugar after 30 7
days. Irradiation dose above 0.5 kGy had cause great damage to the citrus fruit, while 8
0.2-0.4 kGy irradiation treatment had little effect on total sugar content.9
It turned out that citrus fruits treated at doses of 0.2-0.4 kGy had no significant 10
differences in weight loss, soluble solids content, total sugar content and titratable 11
acid content compared with the control group. Fernandes[20] studied the effects of 12
irradiation on chestnut fruits and found that the gamma irradiation doses ≤ 3 kGy did 13
not affect the nutritional and chemical quality of chestnut fruits, which indicated that 14
fruits irradiated at suitable doses would have little harm on its physical properties. 15
According to Farkas[21] , irradiation could reduced storage losses, extended shelf life 16
and/or improved microbiological and parasitological safety of foods. In this study, the 17
similar phenomenon was observed, showing that irradiation doses at proper level18
could prolong the shelf life of Shatang mandarin as well as enhance its appearance 19
quality. We also found that the citrus fruit treated at 0.5 kGy and 0.6 kGy completely 20
decayed in 45 days, suggesting that high dose irradiation treatment had a damaging 21
effect on Citrus fruits, however, at which exactly dose would this happen is still 22
unknown, further studies would be needed to carried out to conform the dosage.23
No significant differences in ascorbic acid between treated fruits and the control 24
were observed in the first 7 days yet it was increased a little bit in control group, 25
which, then sharply decreased on the 30th day and increased again on the 45th26
days. Nevertheless, the ascorbic acid of irradiation treatment groups kept decreasing 27
during the whole experimental period, and this kind of change was much faster in the 28
control than it in irradiation treatment. There were no significant differences between 29
treated groups and the control in ascorbic acid after 15 days and 30 days,30
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respectively.When tested on the 30th day, the ascorbic acid of the treatment groups1
was slightly higher than control but it in groups irradiated at 0.2-0.4 kGy then became 2
lower than control after 45 days treatment. The results illustrated that irradiation 3
treatment doses of 0.2-0.4 kGy on citrus fruits could somehow affect its ascorbic acid 4
content; however, the difference between irradiated samples and the control was not 5
obvious after 30 days of storage at 4 �. 6
The results showed that titratable acid of Shatang mandarin decreased as the 7
storage time extended. There was no significant difference between groups treated by 8
0.2 kGy and 0.3 kGy in titratable acid content when tested on the 7th day and 15th day, 9
but it significantly decreased after 30 and 45 days irradiation treatment in these two 10
groups when it was compared with control (Figure 1.), and the content of titratable 11
acid in groups treated at a dose at 0.3 kGy or higher than it were less than a half of 12
control. It indicated that the irradiation effect on titratable acid content of Shatang 13
mandarin would become serious after 30 days.14
Figure 2 showed that although irradiation treatment had a certain impact on the 15
ascorbic acid content, the ascorbic acid content of irradiation treatment group reduced16
much slower than that of the control. Kaewsuksaeng[22] reported that UV-B treatment 17
induced a gradual increase in citric acid and suppressed the increase of sugar contents 18
during storage. In addition, the ascorbic acid content with or without UV-B treatment 19
decreased during storage, but the decrease in the control was faster than that with 20
UV-B treatment. Others also pointed that irradiation not only affected seed formation 21
in the fruit, but also lowed acidity [23]. From figure 1 we can conclude that titratable 22
acid of Shatang mandarin decreased with the extension of storage time, which 23
revealed that irradiation treatments had significant effect on titratable acid content of 24
Shatang mandarin.25
26
27
Table 1. Weight loss Rate（%）of the citrus fruits after different gamma irradiation 28
treatments.29
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Days in storageSample
7 15 30 45
Control 0.17±0.03a 0.64 ±0.09a 0.96±0.10c 1.22±0.02a
0.2 kGy 0.16±0.05a 0.35±0.01d 0.56±0.03d 0.75±0.02c
0.3 kGy 0.16±0.05a 0.36±0.03d 0.59±0.01d 0.79±0.02bc
0.4 kGy 0.16±0.02a 0.40±0.05cd 0.65±0.05d 0.83±0.004b
0.5 kGy 0.18±0.02a 0.44±0.05bc 1.26±0.09b —
0.6 kGy 0.18±0.02a 0.49±0.01b 1.57±0.07a —
1
Table 2. Decay Rate（%）of the citrus fruits after different gamma irradiation 2
treatments.3
Days in storageSample
7 15 30 45
Control 0.00±0.00c 2.00±1.00c 6.67±1.15c 14.67±2.52b
0.2 kGy 0.00±0.00c 0.00±0.00c 3.00±1.00d 8.00±2.00d
0.3 kGy 0.00±0.00c 0.00±0.00c 3.67±1.15cd 8.33±1.15d
0.4 kGy 0.00±0.00c 1.67±0.58c 5.33±0.58cd 11.33±1.53c
0.5 kGy 21.00±3.61b 55.00±5.00b 92.33±2.52b 100.00±0.00a
0.6 kGy 35.00±5.00a 69.67±4.73a 97.67±2.52a 100.00±0.00a
4
Table 3. Total sugar（g/100 ml）of the citrus fruits after different gamma irradiation 5
treatments.6
Days in storageSample
7 15 30 45
Control 15.42±0.42a 15.11±0.38a 14.99±0.38a 14.65±0.33a
0.2 kGy 15.40±0.42a 15.08±0.38a 14.77±0.37a 14.24±0.29ab
0.3 kGy 15.40±0.42a 14.93±0.37a 14.68±0.35a 14.02±0.26ab
0.4 kGy 15.39±0.42a 14.84±0.35a 14.49±0.32a 13.69±0.29bc
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0.5 kGy 15.37±0.42a 14.66±0.34a 14.16±0.33a —
0.6 kGy 15.07±0.38a 14.15±0.25a 13.98±0.28a —
Note: Date(Table 1, 2 and 3) are presented as the mean±standard deviation of 1
triplicate measurements. Days in storage (7, 15, 30, 45.) mean the days after treatment. 2
Values in the same column with different letters are significantly different (p<0.05).3
4
Figure 1.Chang in content of Titrable acidity after 7, 15, 30, 45 days of different 5
gamma irradiation treated samples and control as compared to time 0 day. Values 6
with an asterisk differ significantly (p < 0.05) from the start of the experiment [CK7
（control）; 0.2 kGy treatment, 0.3 kGy treatment, 0.4 kGy treatment, 0.5 kGy treatment and 0.68
kGy treatment, for parts A=7 days after treatment, B=15 days after treatment, C=30 days after 9
treatment, and D=45 days after treatment respectively].10
11
Figure 2.Chang in content of Ascorbic acid of the citrus fruit after 7, 15, 30, 45 12
days of different gamma irradiation treated samples and control as compared to time 0 13
A B
C D
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day. Values with an asterisk differ significantly (p < 0.05) from the start of the 1
experiment [CK（control）; 0.2 kGy treatment, 0.3 kGy treatment, 0.4 kGy treatment, 0.5 kGy 2
treatment and 0.6 kGy treatment, for parts A=7 days after treatment, B=15 days after treatment, 3
C=30 days after treatment, and D=45 days after treatment respectively].4
5
6
3.2 Enzyme Activities7
Results of the enzymatic analyses in Figure 3 and 4 illustrated that the SOD 8
enzyme activity of citrus fruits with or without irradiation all increased greatly at the 9
first 7 days, and the control showed the highest activity than other irradiation 10
treatment groups (Figure 3). This may attibute to free radicals induced by 11
irradiation. The SOD activity of all groups dropped to a low level after 15 days, it 12
might because the free radical were cleared by SOD enzyme increased before.13
After 30 days, SOD enzyme activity of all groups bounded back to a relatively higher 14
leve again, in which, the value of 0.4 kGy and 0.5 kGy treatment groups 15
A B
C D
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increased greatly. 45 days after irradiation treatment, 0.5 kGy and 0.61
kGy irradiated citrus fruit decayed completely, and the SOD activity of other groups 2
decreased, and the SOD activity of irradiation treatment groups were lower than the 3
control, showing that irradiated fruit produced more free radicals , however, the 4
treated groups had a larger fluctuations in SOD activity than the control group during 5
the whole experimental process; overall, low dose (�0.4 kGy) irradiation could play 6
a role in delaying Citrus Reticulate Blanco fruit senescence as well as in prolonging 7
the storage shelf. 8
SOD catalyzes the dismutation of superoxide anions to produce hydrogen peroxide, 9
which is then removed by catalase, and the two enzymes are thought to extend food 10
freshness by protecting the integrity of membranes [24]. SOD activity in the citrus fruit 11
increased with or without irradiation treatments, but the activity of the enzymes 12
significantly lower than that in the control throughout 7 days of storage at 4� (Figure 13
3.). It may result of free radicals induced by irradiation . SOD is a primary scavenger 14
for superoxide free radicals, which plays a role in the dismutation of superoxide 15
radicals, whereas catalase (CAT), ascorbate peroxidase (APX) and glutathione 16
reductase (GR) activities would contribute, at least to some extent, to the elimination 17
of hydrogen peroxide[25].18
Studies have been carried out a certain correlation browning of fresh fruits and 19
vegetables with tissue POD, POD through the oxidation reaction can lead to 20
deterioration of the quality of fruits and vegetables. The results of Fig. 2 showed 21
that POD activity of Shatang mandarin fruit increased at first place, then decreased as 22
the storage time extended. The POD activity of all experimental groups increased23
after 7 days irradiation, showing a dose-dependent manner; The POD enzyme activity24
of 0.2-0.4 kGy treatment groups were significantly lower than control after 45 days 25
irradiation, And the 0.5 kGy and 0.6 kGy irradiation groups showed the highest POD 26
activity of the whole experiment process, indicated that high dose 27
irradiation would cause damage to the citrus fruit.28
With regard to the effects on enzyme activity, a study by Falguera et al. [26] found a 29
slightly decrease in the activity of POD in fresh apple juices from Golden, Starking 30
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and Fuji, in UV irradiation treatments, this value slightly decreased during the 1
experiment. Meanwhile, in the juice from King David the loss was 70.0%. In this 2
study, a decrease of POD activity was also observed (Figure 4), Shatang 3
mandarin, low acidity, contained ascorbic acid isn't enough to inhibit the activity of 4
POD for long time, a large number of high active POD will lead to deterioration 5
of the quality. The reason of gamma irradiation to extend the shelf life of the 6
fruit might be due to the influence of the basic metabolism of the fruit, 7
suppressing respiratory enzyme activity, inhibiting the release of CO2 and ethylene 8
production, resulting in delayed ripening and senescence; secondly, irradiation could 9
kill microbial spoilage of fruit, and irradiation played a role in preservation. And it 10
suggested that the SOD and POD enzymes played important roles in the citrus fruit 11
senescence, while the mechanism needed to be further explored.12
13
Figure 3.Effect of Co60γ irradiation on the superoxide dismutase (SOD) of the citrus 14
treated with or without irradiation after 7, 15, 30, 45 days at different dose during 15
storage at 4 �.16
17
18
Figure 4.Effect of Co60γ irradiation on the peroxidase (POD) activity of the citrus 19
treated with or without irradiation after 7, 15, 30, 45 days at different dose during 20
storage at 4 �.21
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1
2
The results of effects of Co-60 gamma-irradiation on the quality index and the 3
protective enzyme activities of the citrus fruit during storage. Our studies showed that 4
low dose irradiation (0.2-0.4 kGy) treatments could prolong the shelf life of the citrus 5
fruit and these doses would slightly affect the quality of citrus fruits with an 6
acceptable level. These results showed that certain Co-60 gamma-irradiation could be 7
a promising safety method to control insect pests and extend the shelf life and delay 8
senescence of other kinds of fruits and vegetables.9
4. Conclusions10
Our results suggested that irradiation at the dose range of 0.2-0.4 kGy and in 11
combination with refrigerated storage is an effective post-harvest technique in 12
mitigating the risk of pest and decay of quarantined fruit.13
Acknowledgments14
The researchers gratefully acknowledge the grants from the International Atomic 15
Energy Agency under Research Contract No.15630.16
Conflicts of Interest17
The authors declare no competing financial interest.18
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physico-chemical, nutritional and antioxidant parameters of chestnuts - a review.3
Food Chem Toxicol, 2012.50(9): p.3234-42.4
2. Food, F. and A. Organization., Phytosanitary treatments for regulated pests. 5
ISPM\# 28.. 2009, Food and Agricultural Organization Rome, Italy.6
3. Hallman, G.J., Phytosanitary Applications of Irradiation. COMPREHENSIVE 7
REVIEWS IN FOOD SCIENCE AND FOOD SAFETY, 2011. 10(2): p. 8
143-151.9
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