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Radiation Physics and Chemistry 81 (2012) 1076–1078
Contents lists available at SciVerse ScienceDirect
Radiation Physics and Chemistry
journal homepage: www.elsevier.com/locate/radphyschem
Effect of gamma irradiation on microbiological, chemical, and sensory
properties of fresh ashitaba and kale juices
Cheorun Jo a, Dong Uk Ahn b, Kyung Haeng Lee c,n
a
Department of Animal Science and Biotechnology, Chungnam National University, Daejeon 305-764, South Korea
Department of Animal Science, Iowa State University, Ames, IA 50011, USA
c
Department of Food Science and Nutrition, Chungju National University, Jeungpyeong 368-701, South Korea
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 19 May 2011
Accepted 26 November 2011
Available online 4 December 2011
Due to the popularity of health effects upon intake of fresh fruits and vegetables, the demand for fresh
vegetables and fruit juices has rapidly increased. However, currently, washing is the only procedure for
reducing contaminated microorganisms, which obviously limits the shelf-life of fresh vegetable juice
(less than 3 days). In this study, we examined the effects of irradiation on the microbiological, chemical
and sensory properties of ashitaba and kale juices for industrial application and possible shelf-life
extension. Freshly made ashitaba and kale juices already had 2.3 105 and 9.5 104 CFU/mL, respectively. Irradiation of 5 kGy induced higher than 2 decimal reductions in the microbial level, which was
consistently maintained during storage for 7 days under refrigerated conditions. Total content of ascorbic
acid in vegetable juice decreased upon irradiation in a dose-dependent manner. However, the content of
flavonoids did not change, whereas that of polyphenols increased upon irradiation. In sensory evaluation,
the ashitaba and kale juices without irradiation (control) scored lower than the irradiated samples after
1 and 3 days, respectively. This study confirms that irradiation is an effective method for sterilizing fresh
vegetable juice without compromising sensory property, which cannot be subjected to heat pasteurization due to changes in the bioactivities of the products.
& 2011 Elsevier Ltd. All rights reserved.
Keywords:
Gamma irradiation
Vegetable juice
Microbiological properties
Chemical properties
Sensory properties
1. Introduction
The association of high consumption of vegetables and fruits
and low incidence of certain chronic diseases (Byers and Perry,
1992) is evidence of the health effects upon consuming fresh
fruits and vegetables. Vegetable juice is manufactured by pressuring minced vegetables without cooking to provide easier absorption of nutrients and bioactive compounds (Song et al., 2007).
However, food safety is always one of the most important
issues in the food industry. Since there is no heat processing in
the manufacturing of vegetable juice, more hygienic procedures
during manufacturing should be employed. In current processing
procedures, washing is the only step that can reduce the number
of contaminating microorganisms. Thus, with increasing demand
for nutritious, fresh-like food products with high organoleptic
quality and adequate shelf-life, non-thermal inactivation methods
have become necessary, especially for industrial applications (Lee
et al., 2009).
Non-thermal sterilization methods have been developed,
including irradiation, high pressure, pulsed electric fields, low-
n
Corresponding author. Tel.: þ82 43 820 5334; fax: þ82 43 820 5850.
E-mail address: leekh@cjnu.ac.kr (K.H. Lee).
0969-806X/$ - see front matter & 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.radphyschem.2011.11.065
temperature plasma, and others (Yun et al., 2010). Each nonthermal method has its own advantages and disadvantages.
Among them, irradiation can be one of the most effective and
safe technologies for decontamination of vegetables, but research
on this particular food category is still limited.
The objective of this study was to examine the effects of
irradiation on the microbiological, chemical, and sensory properties of fresh ashitaba and kale juices for industrial applications.
These vegetable juices are successfully commercialized and currently available in Korea.
2. Materials and methods
Ashitaba (Angelica keiskei) juice was made from 100% fresh
ashitaba while kale (Brassica loeracea var. acephala) juice
was made from fresh kale juice (75%), apple juice concentrate
(69.0 Brix, 6%), pineapple concentrate (60.0 Brix, 5%), and water
(4%). The samples were the same as those available in the market
and were purchased from a local production company. The
samples were packaged in a polyethylene pouch and irradiated
in a cobalt-60 gamma irradiator. The applied doses in this study
were 0, 1, 3, and 5 kGy. The actual doses were within 75.4% of
the target dose.
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C. Jo et al. / Radiation Physics and Chemistry 81 (2012) 1076–1078
1077
105 CFU/mL) (KFDA, 2008). This must have been due to microorganisms in the soil that attached to the vegetables. During the
washing process, pressured water and air droplets are used to
decontaminate the microorganisms, but if they are poorly managed, the original contamination can remain very high even in
freshly made vegetable juice (Cho et al., 2009). From the results,
it was thought that sterilization process is necessary to ensure
minimal adverse changes in quality.
When fresh ashitaba juice was irradiated, the number of TAB
decreased in a dose-dependent manner after irradiation and grew
very slowly during storage thereafter (Fig. 1). Fresh kale juice
showed 9.5 104 CFU/mL at the beginning, but this increased
to higher than the legal limit just after 1 day (1.1 105 CFU/mL).
Higher than 2 decimal reductions in TAB in kale juice were
obtained upon irradiation at 5 kGy.
The number of coliforms in the ashitaba and kale juices were
102 CFU/mL after manufacturing, but 90% of the coliforms were
inactivated by 3 kGy of irradiation in both the vegetable juices
(Fig. 2). No detectable viable cells were found at 5 kGy. The
sudden increase in the number of coliforms in the fresh ashitaba
juice at day 5 might be due to the insufficient inactivation at the
initial stage after 1 kGy of irradiation.
The contents of the main bioactive compounds, including
ascorbic acid, flavonoids, and polyphenolics, in both the vegetable
juices were measured to examine the effects of irradiation. The
ascorbic acid content of ashitaba juice was 8.47 mg% after manufacturing, which was not different from the sample irradiated at
Media for the enumeration of total aerobic bacteria (TAB) and
coliform bacteria were standard plate count agar and eosin
methylene blue agar, respectively. The contents of ascorbic acid,
flavonoids, and total polyphenols in the two different vegetable
juices were measured by the methods of Jagota and Dani (1982),
Moreno et al. (2000), and AOAC (1995), respectively, to verify the
changes in chemical properties of the irradiated vegetable juices.
Sensory evaluation was conducted by 12 semi-trained panelists
0, 1, and 3 days after the irradiation process. The panelists were
educated, and they evaluated the preference of each sample
individually. Preference is the overall acceptance of panelists for
the samples including color, taste, odor, and mouthfeel. The acceptance was recorded on a 5-point hedonic scales (1¼extremely
dislike, 5¼extremely like).
The data were collected and analyzed by SAS software (version
8.02; SAS Institute, Cary, NC, USA). Mean values and standard
errors of the mean (SEM) are reported, and significant difference
was defined at Po0.05. Differences among the mean values were
analyzed by Duncan’s multiple range test.
3. Results and discussions
Ashitaba and kale are the most widely used raw materials in
the fresh vegetable juice industry. The total aerobic bacteria (TAB)
number in fresh ashitaba juice was 2.3 106 CFU/mL (Fig. 1),
which was already higher than the legal standard (less than
1e+8
No. of viable cell (CFU/mL)
Ashitaba
Kale
Control
1 kGy
3 kGy
5 kGy
1e+7
1e+6
1e+5
1e+4
1e+3
1e+2
0
1
2
3
4
5
6
Storage period (day)
7 0
1
2
3
4
5
6
Storage period (day)
7
Fig. 1. Total aerobic bacterial count (CFU/mL) in fresh ashitaba and kale juices after gamma irradiation and during storage at 4 1C.
No. of viabla cell (CFU/mL)
10000
Ashitaba
Control
1 kGy
3 kGy
1000
Kale
100
10
1
0
1
2
3
4
5
6
Storage period (day)
7 0
1
2
3
4
5
6
Storage period (day)
7
Fig. 2. Coliforms (CFU/mL) in fresh ashitaba and kale juices after gamma irradiation and during storage at 4 1C.
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C. Jo et al. / Radiation Physics and Chemistry 81 (2012) 1076–1078
Content of flavonoid (mg%)
Content of ascorbic acid (mg%)
Ascorbic acid
10
8
6
4
2
0
Control 1 kGy 3 kGy 5 kGy
Treatment
80
Ashitaba
kale
Flavonoid
60
40
20
0
Control 1 kGy 3 kGy 5 kGy
Treatment
Content of polyphenols (υg/mL)
120
12
Polyphenols
100
80
60
40
20
0
Control 1 kGy 3 kGy 5 kGy
Treatment
Fig. 3. Contents of ascorbic acid (mg%), flavonoids (mg%), and polyphenols (mg/mL) in gamma irradiated ashitaba and kale juices.
1 kGy (Fig. 3). However, the content of ascorbic acid was reduced
significantly when 3 and 5 kGy of irradiation were applied. On the
other hand, the flavonoid content did not change, whereas the
amount of polyphenols increased slightly but significantly upon
irradiation of 3 and 5 kGy. Previous increases in biological activity
upon irradiation of biomaterials have been reported (Kim et al.,
2011; Jo et al., 2008).
Kale juice originally had higher content of ascorbic acid than
ashitaba juice, but irradiation decreased the content of ascorbic
acid to 54% of the original amount (Fig. 3). The results show that
the ascorbic acid content of kale juice irradiated at 5 kGy was
similar to that of ashitaba juice at 3 kGy. The content of flavonoids
did not change, but that of polyphenols was higher in kale juice
irradiated at 5 kGy, which was similar to that in ashitaba juice
(Fig. 3).
In general, sensory evaluation showed that both the vegetable
juices displayed no significant differences (data not shown). As
storage period progressed the sensory scores were lowered, and
the irradiated samples scored slightly but significantly higher.
Irradiation may produce off-flavor and off-color problems (Yun
et al., 2010). However, vegetable juice inherently has a very
strong flavor; thus, there was no distinctive irradiation-induced
off-flavor reported in the sensory analysis when irradiation was
applied up to 5 kGy.
4. Conclusion
This study confirms that irradiation was an effective method
for sterilizing fresh vegetable juice without compromising sensory properties, which cannot be subjected to heat pasteurization
due to changes in the bioactivities of the products.
Acknowledgment
This work was carried out with the support of Technology
Development Program, Ministry for Food Agriculture, Forestry,
and Fishery, Republic of Korea.
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