ORIGINAL ARTICLE
UV-C treatment on physiological response of potato (Solanum
tuberosum L.) during low temperature storage
Qiong Lin
1
•
Yajing Xie
1
•
Wei Liu
1
•
Jie Zhang
1
•
Shuzhen Cheng
1
•
Xinfang Xie
1
•
Wenqiang Guan
2
•
Zhidong Wang
1
Revised: 28 November 2016 / Accepted: 30 November 2016 / Published online: 26 December 2016
Ó Association of Food Scientists & Technologists (India) 2016
Abstract The storage of potato tuber (Solanum tuberosum
L.) at low temperatures minimizes sprouting and disease
but can cause cold-induced sweetening (CIS), which leads
to the production of the cancerogenic substance acrylamide
during the frying processing. The aim of this research was
to investigate the effects of UV-C treatment on CIS in cold
stored potato tuber. ‘Atlantic’ potatoes were treated with
UV-C for an hour and then stored at 4 °C up to 28 days.
The UV-C treatment significantly prevented the increase of
malondialdehyde content (an indicator of the prevention of
oxidative injury) in potato cells during storage. The accu-
mulation of reducing sugars, particularly fructose and
glucose, was significantly reduced by UV-C treatment
possibly due to the regulation of the gene cascade, sucrose
phosphate synthase, invertase inhibitor 1/3, and invertase 1
in potato tuber, which were observed to be differently
expressed between treated and untreated potatoes during
low temperature storage. In summary, UV-C treatment
prevented the existence of oxidative injury in potato cells,
thus, lowered the amount of reducing sugar accumulation
during low temperature storage of potato tubers.
Keywords UV-C Cold-induced sweetening Potato
tuber Storage Gene expression
Introduction
Low temperature storage is an effective and convenient
way to prolong the processing period of potato tubers, by
inhibiting sprouting and decay. However, low temperature
storage has been shown to accelerate the cold-induced
sweetening (CIS) of potato during storage, an important
element determining the frying quality of potato tubers
(Dale and Bradshaw 2003; Vijay et al. 2016). This is
mainly because of the occurrence of Maillard reaction,
which generates dark colored products as well as the
probable carcinogen- acrylamide during frying processing,
is increased in susceptible potatoes (Mottram et al. 2002;
Qiong Lin and Yajing Xie contributed equally to this work.
Electronic supplementary material The online version of this
article (doi:10.1007/s13197-016-2433-3) contains supplementary
material, which is available to authorized users.
& Zhidong Wang
wangzhidong@caas.cn
Qiong Lin
linqiong@caas.cn
Yajing Xie
xieyajing@caas.cn
Wei Liu
liuwei@caas.cn
Jie Zhang
zhangjie@caas.cn
Shuzhen Cheng
chengshuzhen@caas.cn
Xinfang Xie
xiexinfang@caas.cn
Wenqiang Guan
gwq18@163.com
1
Institute of Food Science and Technology, Chinese Academy
of Agricultural Sciences/Key Opening Laboratory of
Agricultural Products Processing and Quality Control,
Ministry of Agriculture, Beijing 100193, China
2
Tianjin Key Laboratory of Food Biotechnology, College of
Biotechnology and Food Science, Tianjin University of
Commerce, Tianjin 300134, China
123
J Food Sci Technol (January 2017) 54(1):55–61
DOI 10.1007/s13197-016-2433-3
Shallenberger et al. 2002). To alleviate the problem,
research has been focused on decreasing the content of
total reducing sugars in potato tubers as the most effective
method to decrease acrylamide content in fried potatoes
(Muttucumaru et al. 2008).
CIS has been widely studied in potato tubers (Fou-
karaki et al. 2016; Mehdi et al. 2013; Wiberley-Bradford
et al. 2016), and it has been reported that CIS occurs due
to an imbalance between the metabolism of starch and
sugar (Ezekiel et al. 2010). The degradation pathway from
starch to hexoses is complex, and several enzymes are
involved in this progress, including sucrose synthase
(SuSy), sucrose phosphate synthase (SPS), ADP-glucose
pyrophosphorylase small subunit (AGPase), granule-
bound starch synthase (GBSS) (Wiberley-Bradford et al.
2014). Researchers proposed that the sucrose enters into
the vacuole, where it can be cleaved to glucose and
fructose, which was catalyzed by acid invertase (INV)
(Sowokinos 2001). However, the activity of INV, which
can be reversely regulated by invertase inhibitor (INH),
has been reported to be the most important factor in
regulating the contents of reducing sugars (Mckenzie
et al. 2005, 2013). The regulation of sugar metabolism
was clearly understood in potato tubers, but how this
process was regulated under different stress conditions or
treatments remains poorly studied.
UV-C treatment is a cheap, safe and convenient tech-
nique for postharvest storage, which has been widely used
in controlling microorganism in many fresh products
during storage (Allende and Artes 2003). UV-C is also an
effective measure to maintain the quality of fresh fruit
and vegetables, such as strawberry (Xie et al. 2015).
Researches have reported that UV-C treatment may
increase the contents of nutritional metabolites in fresh
fruits and vegetables (Cisneros-Zevallos 2003). However,
a previous report indicated that the content of vitamin C
was decreased by UV-C treatment in fresh-cut fruits
(Alothman et al. 2009). Several researches have been
conducted on potato tubers, for example, UV-C reduced
sprout growth in potato with no deleterious effects on
tuber quality (Cools et al. 2014). Little research has been
conducted on the effect of UV-C treatment on CIS of
potato tuber.
In the present study, ‘Atlantic’ potatoes were treated
with UV-C for an hour on each side, and then stored at
4 °C for up to 28 days. The variation of weight loss,
respiration intensity, sugars and expressions of starch-
sugar metabolism related genes were analyzed. The
objective is to investigate the effects of UV-C treatment
on physiological response of potato during low tempera-
ture storage.
Materials and methods
Plant material and treatments
Tubers of ‘Atlantic’ potato (Solanum tuberosum L.) with
uniform size were harvested from orchards in Zhangjiakou,
Beijing. After curing for seven days under room tempera-
ture, potatoes were placed at 20 cm below UV-C lamps,
with 254 nm UV photons, and irradiated for 1 h on each
side. After irradiation, both the treated and untreated
potatoes were stored at 4 °C with 85–95% relative
humidity (RH) and sampled at 0, 3, 7, 14 and 28 days after
treatment. Each sample consisted of twelve potatoes, which
were divided into three replicates. The peeled flesh of
potatoes at each sampling point was stored at -80 °C.
Weight loss analysis
The weight for each potato was recorded at each sampling
point. The weight loss rate was calculated according to the
following algorithm: Weight loss (%) = (m
0
- m)/
m
0
9 100%, where ‘m
0
’ represents the potato weight at the
first day, ‘m’ represents weight of potato at each sampling
point of both control and treatments.
CO
2
production analysis
Three potatoes were sealed in one bottle. The gas con-
stituents of each treatment were analyzed by gas analyzer
(checkmate 3, PBI-DanSenser, Denmark) after an incuba-
tion of 2 h at 4 °C on each sampling day. The respiration
rate was calculated based on the gas constituent variation.
Four replicates were used in this analysis.
Sugar content analysis
A total of 0.2 g (dry weight) sample powder was homog-
enized with 4 mL of 80% ethanol. The mixture was
extracted with ultrasonic for 30 min at room temperature,
and centrifuged at 10,0009g for 15 min. Aliquots of 1 mL
of the upper phase were dried under pure nitrogen. The
residue was dissolved in 1 mL ddH
2
O and filtered through
a membrane with 0.22 lm pore size.
A volume of 10 lL for each sample was injected into
the ion chromatograph (ICS-3000, Dionex, USA) fitted
56 J Food Sci Technol (January 2017) 54(1):55–61
123
with Carbo PacTMPA20 column (3 mm 9 150 mm). The
column temperature was 35 °C, and the flow rate was
0.5 mL min
-1
. The gradient elution buffer was used as
follows: A, ddH
2
O; B, 250 mmol L
-1
NaOH; Equal gra-
dient of 92.5% A and 7.5% B were used for elution. A
pulsed amperometric detector with gold electrode was
used. Identification of the substances was according to the
retention time (RT) of standard compounds. The contents
of glucose, fructose, sucrose and galactose were calculated
by comparison with standard curves. Total reducing sugar
was calculated as total amount of glucose, fructose and
galactose.
MDA content analysis
Malondialdehyde (MDA) content was determined based on
the method described by Heath and Packer 1968 with modi-
fications. One gram (dry weight) of each sample was
homogenized in 10 mL 10% (w/v) trichloroacetic acid, and
then centrifuged at 10,0009g for 10 min. Thiobarbituric acid
(3 mL 0.67%) were added into 3 mL of supernatant. The
mixture was incubated in a boiling water bath for 15 min, and
then centrifuged. The MDA content was calculated based on
the absorbencies at 450, 532 and 600 nm, according to the
following formula: MDA (mol L
-1
) = [6.45 9 (-
A
532
- A
600
) - 0.56 9 A
450
] 9 10
-6
. The MDA contents
in the samples were calculated and used for analysis.
RNA extraction and cDNA synthesis
Total RNA of the potato tuber was extracted using RNA prep
Pure Plant Kit (Tiangen, China). First strand cDNA was
synthesized from 1 lg RNA, after digestion of genomic
DNA, using iScriptTM cDNA Synthesis Kit (Bio-Rad).
Three biological replicates were included in this analysis.
Quantitative real-time PCR (qRT-PCR)
Primers used in the research were included in supplemen-
tary Table 1. The b-tubulin2 gene was included as an
internal control, and was shown to be stable in the condi-
tions used (data not shown). The SuSy, SPS, AGPase,
GBSS, INV and INH gene expression studies were con-
ducted on Power SYBR
Ò
Green PCR Master Mix kit
(Applied Biosystems) and ABI 7500 instrument (Applied
Biosystems).
Data analysis
The figures were drawn using Origin 8.6 software (Mi-
crocal Software Inc., Northampton, MA, USA). Least
significant difference (LSD) at the 0.05 level was calcu-
lated by SPSS Statistics 22 Software.
Results
Physiological response of potato under UV-C
treatment
Weight loss rate was observed to increase continuously in
both the control and the UV-C treated potatoes during the
whole storage period, with 0.67 and 0.77% weight loss on
28 days storage in control (CK) and UV-C treated potatoes,
respectively. No significant difference was observed
between the control and the UV-C treated potatoes during
storage (Fig. 1a). A rapid drop of CO
2
production (3.6- and
2.6-fold in CK and UV-C treated potatoes, respectively)
occurred on 3 days storage and was relatively remained
stable during the subsequent low temperature storage. No
significant difference was observed between the control
and UV-C treated potatoes (Fig. 1b).
Resistance response of potato under UV-C
treatment
Malondialdehyde is the main product of cell membrane
lipid peroxidation. Throughout the storage period, MDA
content increased in both the control and the treated sam-
ples. Compared with the UV-C treated potatoes, the MDA
content in the CK samples increased more rapidly. Sig-
nificant differences were observed between the treatments
at 7 and 14 days storage, with 1.28 9 10
-6
and
Fig. 1 Effects of UV-C treatment on weight loss (a) and CO
2
production (b) in potato tubers during low temperature storage. The
error bars represent the standard errors. LSDs represent least
significant differences at the 0.05 level
J Food Sci Technol (January 2017) 54(1):55–61 57
123
1.48 9 10
-6
mol kg
-1
higher MDA content than control,
respectively (Fig. 2). These results indicated that UV-C
treatment could prevent the existence of the potato oxida-
tive injury during storage.
Total reducing sugar levels increased in the potato
tubers of both the control and the UV-C treatment during
storage. Compared with UV-C treated potatoes, total
reducing sugar in control potatoes increased more rapidly,
reaching a content of 6.48 g kg
-1
on 28 days storage,
which was 1.65 times higher than that in UV-C treated
potatoes at the same stage. Total reducing sugar in control
samples was constantly higher than that of the UV-C
treated samples, by 1.65–2.02-fold, during the whole
storage period. Thus, UV-C treatment was observed to be
effective in alleviating the reducing sugar accumulation in
potato tubers during low temperature storage (Fig. 3).
Individual sugar contents variation
Four soluble sugar compounds were measured in present
research, including fructose, glucose, sucrose and galactose,
with sucrose being considered as the predominant soluble
sugar in the mature potato tuber. Fructose and glucose con-
tents during postharvest storage of potato increased contin-
uously in both CK and UV-C treated samples. The fructose
and glucose contents in the CK samples increased more
rapidly than UV-C treated samples, and significant differ-
ences were observed between the CK and the UV-C treated
potatoes. After 28 days storage, fructose and glucose in CK
potatoes were 0.92 and 1.62 g kg
-1
higher than that in UV-C
treated potatoes, respectively (Fig. 4a, b). Sucrose content
increased continuously during the whole storage period in
both samples, while galactose decreased slightly and then
increased during the later storage stages. No significant
difference was observed in sucrose and galactose contents
between CK and UV-C treated potatoes (Fig. 4c, d).
Expressions of sugar metabolism related genes
Expression of PtAGPase was irregular in both control
and UV-C treated potatoes during storage, no signifi-
cant difference was observed between two treatments
(Fig. 5a). PtGBSS expression increased rapidly during
the early storage stage and dropped rapidly during the
later stage, no significant difference was investigated
between CK and UV-C treated samples (Fig. 5b). The
expression of PtSPS increased continuously during the
whole storage period in both control and treatment.
Significant differences between CK and UV-C treated
samples were observed on 28 days storage, where
expression of PtSPS in the CK was 2.41 times higher
than that in the UV-C treated samples (Fig. 5c). The
expression of PtSuSy was similar with PtGBSS
(Fig. 5d).
PtINH1 increased continuously during the posthar-
vest storage in both potato samples, significant differ-
ences in PtINH1 expression were observed at 28 days
storage, where PtINH1 expression in the CK was 1.95
times higher than that in UV-C treated potatoes
(Fig. 6a). PtINH2 expression increased during the later
storage, but no significant difference was observed
between samples (Fig. 6b). Significant differences in
PtINH3 expression were observed on 3 and 28 days
storage, which showed 68 and 20% higher expressions
in UV-C treated potatoes than control samples 3 and
28 days storage, respectively (Fig. 6c). The expression
of PtINV1 was induced, by 6.3-fold, by UV-C treatment
at 3 days storage, but showed a relatively constant
trend during later storage period in the UV-C treatment.
Significant difference was observed between samples at
28 days storage (Fig. 6d).
Fig. 2 Effects of UV-C treatment on MDA content in potato tubers
during low temperature storage. The error bars represent the standard
errors. LSDs represent least significant differences at the 0.05 level
Fig. 3 Effects of UV-C treatment on total reducing sugar content in
potato tubers during low temperature storage. The error bars
represent the standard errors. LSDs represent least significant
differences at the 0.05 level
58 J Food Sci Technol (January 2017) 54(1):55–61
123
Discussion
UV-C significantly decreased the MDA content in potato
tubers during cold storage. Such a response could indicate a
reduction in membrane injury by UV-C pretreatment.
Previously it has been reported that UV-C could increase
the ability of stress resistance in various products. For
example, UV-C treatment has been shown to modify the
cell structure in tomato fruit surface and thereby could play
an important role in the resistance of infection (Charles
et al. 2008). UV-C has also been shown to increase the
levels of reactive oxygen species (ROS) in both eukaryotic
and prokaryotic organisms (Salma et al. 2016), change the
membrane fatty acid composition of cells (Ghorbal et al.
2013), and enhance the antioxidant activity of products
(Wu et al. 2016). Thus, it can be concluded that UV-C
pretreatment promotes the ability of stress resistance in
potato tuber during cold storage.
Sugar accumulation is a response phenomenon under
different stresses, such as cold stress (Malone et al. 2006),
osmotic and salinity stress (Watanabe et al. 2012), and
water stress (Kameli and Lo
¨
sel 1996). This may related to
the fact that the sugars are effective in the regulation of
osmotic pressure in plant cells. Researchers have also
shown that over-expression of vacuole sugar transporter
AtSWEET16 may modify the process of stress tolerance in
Fig. 4 Effects of UV-C
treatment on fructose (a),
glucose (b), sucrose (c) and
galactose (d) contents variation
in potato tubers during low
temperature storage. The error
bars represent the standard
errors. LSDs represent least
significant differences at the
0.05 level
Fig. 5 Expressions of
PtAGPase (a), PtGBSS (b),
PtSPS (c) and PtSuSy (d)in
control and UV-C treated potato
tubers during low temperature
storage. The error bars
represent the standard errors.
LSDs represent least significant
differences at the 0.05 level
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123