全 文 ：316 2014, Vol.35, No.02 食品科学 ※包装贮运
Physiological and Biochemical Responses of Gynura bicolor D.C to
Phytic Acid during Storage
JIANG Li, JIANG Juan, ZHANG Li, FU Lin-ran, YU Zhi-fang*
(College of Food Science and Technology, Nanjing Agricultural University, Nanjing 210095, China)
Abstract: The effect of pretreatment with phytic acid (PA) on physiological and biochemical changes of Gynura bicolor
D.C during storage was investigated. Gynura bicolor D.C leaves were treated with 0.1, 0.5 and 1 mmol/L PA, respectively
and control samples were those treated with water. Both experimental and control samples were wrapped in 15 μm thick
high-density polypropylene (HDPE) bags and stored at 0 ℃ for 15 days. Physiological and biochemical indices, including
decay index, respiration rate, relative leakage, the activities of polyphenol oxidase (PPO), peroxidase (POD), catalase (CAT)
and superoxide dismutase (SOD), and the contents of malondialdehyde (MDA) and superoxide anion free radicals (O2－·),
were tested every 5 days. All PA treatments inhibited obvious physiological and biological reactions in Gynura bicolor D.C
leaves. Particularly, 0.5 mmol/L PA delayed the senescence of Gynura bicolor D.C leaves effectively by decreasing the
incidence of decay, maintaining low relative leakage, retarding the accumulation of O2－· and MDA, inhibiting respiration
rate and PPO activity, and enhancing the activities of POD and SOD. Therefore, PA treatment is potentially applicable in
extending the storage life of Gynura bicolor D.C.
Key words: Gynura bicolor D.C; phytic acid; storage
采后植酸处理对紫背天葵贮藏期间生理生化反应的影响
姜 丽，蒋 娟，张 丽，傅淋然，郁志芳*
(南京农业大学食品科技学院，江苏 南京 210095)
摘 要：以紫背天葵为试材，采用不同浓度（0.1、0.5 mmol/L和1 mmol/L）植酸处理后，高密度聚乙烯袋（15 μm
厚）挽口包装，并置于0 ℃条件下贮藏15 d，每5 d测定一次生理指标，包括腐烂率、呼吸强度、细胞膜渗透率、
多酚氧化酶（PPO）、过氧化物酶（POD）、过氧化氢酶（CAT）、超氧化物岐化酶（SOD）的酶活力和丙二醛
（MDA）和超氧阴离子自由基（O2－·）含量。结果表明，所有植酸处理组均可不同程度的抑制采后紫背天葵的生
理生化反应，并延缓衰老。其中，0.5 mmol/L植酸处理有效减小MDA和O2－·的积累，维持了较好的细胞膜的完整
性，在抑制呼吸速率和PPO活性、增强POD和SOD活性方面也效果显著，由此说明，0.5 mmol/L植酸处理可以有效
提高紫背天葵贮藏生理品质，延缓衰老。
关键词：紫背天葵；植酸；保鲜
中图分类号：TS255.3 文献标志码：A 文章编号：1002-6630（2014）02-0316-06
doi:10.7506/spkx1002-6630-201402062
收稿日期：2013-02-22
基金项目：南京农业大学青年发展基金项目（KJ2011015）；江苏高校优势学科建设工程资助项目（PAPD）；
国家自然科学基金青年科学基金项目（31301576）；中央高校基本科研业务费专项（KYZ201319）
作者简介：姜丽（1982—），女，讲师，博士，研究方向为食品科学。E-mail：jiangli@njau.edu.cn
*通信作者：郁志芳（1960—），男，教授，博士，研究方向为新鲜农产品采后生物学和处理技术。E-mail：yuzhi88@yahoo.com.cn
Gynura bicolor D.C (Gynura, Composite Gynura cass),
a perennial wild leafy vegetable in subtropical and temperate
zones, is widely distributed in south China[1]. Gynura is rich in
crude protein, edible fiber, fat, amino acid and flavonoid[2-3],
and has been used as folk medicines, antioxidant, and natural
pigment throughout Asia for centuries[4]. Recently, particular
attention has been paid to its nutritional value, antioxidant
activities[1] and anthocyanin extracts[4]. However, postharvest
decay limits the commercial application of Gynura, and the
mechanism of senescence has not yet been reported.
※包装贮运 食品科学 2014, Vol.35, No.02 317
Vegetables slathered with chemical preservatives
may cause allergic reactions with cancerogenic potential in
sensitive individuals. Therefore, natural preservatives have
been preferred by consumers and industry for preserving
fresh vegetables and treating minimally processed ones.
Phytic acid (PA, myo-inositol hexaphosphate acid), as a
secondary metabolite in plant, is a highly phosphorylated
molecule abundant in edible legumes, cereals, oil seeds
and other plants[5]. PA is also applicable in food industry
as a chemopreventive agent against cancers[6]. Graf et al.[7]
considered that PA might play an important role in the
natural and artificial preservation of oxidized materials as an
available natural antioxidant.
PA is an anti-browning and senescence agent for
several harvested vegetables[7], but it has never been used for
postharvest Gynura. Thus, this study focused on investigating
the physiological response of Gynura leaves to exogenous PA
as well as the suitable concentration for practice.
1 Materials and Methods
1.1 Material and treatment
Gynuras were harvested from a commercial farmland in
Shanghai, China. The leaves were pre-cooled to 2–5 ℃ and
transferred to the laboratory by refrigerated vehicle. Leaves
without defects (pest-damaged, bruised and defective) were
selected and randomly divided into 4 lots, and then treated
with water (control), and PA at 0.1, 0.5 mmol/L or 1 mmol/L
for 10 min at 20 ℃, respectively. After drying the surface in
air at room temperature, each treatment was packaged with
high-density polypropylene (HDPE, thickness: 15 μm;
size: 25 cm × 38 cm) plastic bags and stored at (0 ± 1) ℃
for 15 days. All the parameters were measured every 5 days
and only the leaves of Gynura were used.
1.2 Methods
1.2.1 Decay
According to Jiang Li et al.’s[8] method, about 500 g
leaves from each treatment were used, and the decay states
were graded as: 0, no decay; 1, decay rate lower than l/3;
2, 1/3–2/3 decay; 3, decay>2/3. Decay rate was calculated
according to the following formula:
Decay index/% = (1×N1＋2×N2＋3×N3/(3×N)) ×100
where N is the total number of leaves showing different
degrees of decay.
1.2.2 Respiration rate
A glass plate containing 20 mL 0.4 mol/L NaOH was
added, which was used to absorb the CO2 produced by leaves
during respiration process, to the bottom of an glass jar. Then
leaves (300 g) was transferred into the jar to separate sample
material and NaOH solution; and fi nally, the jar was sealed by
glass cover. After 1 h, the NaOH was transferred into beaker
and titrated with 0.2 mol/L oxalic acid. The respiratory rate
was expressed as the moles of CO2 produced per kilogram in
an hour (mmol/kg·h)[9].
1.2.3 Relative leakage rate
Relative leakage rate was determined according to the
method of Li Hesheng[10]. Leaf discs (1 g) were rinsed and
incubated in 20 mL of distilled water for 1 h, and then the
initial electrolyte leakage was monitored with a conductivity
meter (DDS-11A, China). Each sample was continually
rinsed for 4 h after being boiled for 5 min and the final
electrolyte leakage (total electrolyte) was monitored again.
Relative leakage rate was defined as the percent of initial
electrolyte.
1.2.4 Malondialdehyde
To measure malondialdehyde (MDA) content[11], 1 g
tissues were homogenized in 5.0 mL of 10% TCA. After
centrifugation (10 000 r/min for 15 min at 4 ℃), 2.0 mL of
supernatant was mixed with 2.0 mL of 0.67% TBA in a test
tube, and then water-bathed at 100 ℃ for 30 min, which
was followed by cooling and centrifugation (10 000 r/min,
15 min). Then the supernatant was measured at 450, 532 nm
and 600 nm with distilled water as the blank.
1.2.5 Superoxide anion radical
To measure O2
－� content[12], 1 g tissues were
homogenized in 5.0 mL of 65 mmol/L PBS (pH 7.8), added
1.0 mL of 10 mmol/L muriatic acid hydroxylamine and
1.0 mL of 0.1 mol/L EDTA, and rubbed in dark. After
centrifugation (10 000 r/min for 15 min at 4 ℃), 2.0 mL of
supernatant was water-bathed with 2.0 mL of 17 mmol/L
para-aminobenzene sulfonic acid and 2.0 mL of 7 mmol/L
α-naphthylamine for 15 min at 40 ℃, and then fully
mixed with 3 mL of ether. After another centrifugation
(10 000 r/min, 15 min), the water phase was sucked out to be
measured at 530 nm (distilled water was used as the blank), and
a standard curve was established with sodium nitrite.
1.2.6 Polyphenol oxidase
Polyphenol oxidase (PPO) activity was detected by
the Xu Langlai et al.[13] method. Briefly, 0.5 g tissues of the
leaves were homogenized in 6 mL of 50 mmol/L phosphate
buffer (pH 6.4) and supernatant from the homogenate after
centrifugation (10 000×g for 30 min at 4 ℃) was collected
318 2014, Vol.35, No.02 食品科学 ※包装贮运
as the crude enzyme. PPO activity was determined in 3.1 mL
of reaction mixture containing 2 mL of 0.1 mol/L acetate
buffer (pH 5.4), 1 mL of 50 mmol/L catechol and 0.1 mL of
enzyme. Oxidation of guaiacol was followed by the increase
of absorbance at 460 nm (Unic-2802).
1.2.7 Peroxidase
Peroxidase (POD) activity was detected by determining
guaiacol oxidation at 460 nm by H2O2
[14]. Briefly, 0.5 g tissues
of the leaves were homogenized in 6 mL of 50 mmol/L
phosphate buffer containing 50 mmol/L NaHSO3 (pH 8.7)
and supernatant from the homogenate after centrifugation
(10 000×g for 30 min at 4 ℃) was collected as the crude
enzyme. POD activity was determined in 3.2 mL of reaction
mixture containing 2 mL of 0.1 mol/L acetate buffer (pH 5.4),
1 mL of 0.25% guaiacol, 0.1 mL of extract and 0.1 mL of
0.75% H2O2, and was followed by the decrease of absorbance
at 460 nm.
1.2.8 Catalase
The procedure of Zheng Xiaolin et al.[14] was modified
slightly to measure catalase (CAT) activity. Briefly, 0.5 g leafy
tissues were homogenized in 6 mL of 50 mmol/L phosphate
buffer (pH 7.8) and the supernatant after centrifugation
(10 000 r/min for 15 min at 4 ℃) was collected as enzyme
extracts. CAT activity was determined in 3.1 mL of reaction
mixture containing 2 mL of distilled water, 1 mL of 0.2%
H2O2 and 0.1 mL of enzyme, and was followed by the
decrease of absorbance at 240 nm.
One unit (U) of PPO, POD and CAT activities was
defined as the amount that enzyme decreased the absorbance
by 0.001 per minute[15].
1.2.9 Superoxide dismutase
To measure superoxide dismutase (SOD) activities[16], 0.5 g
tissues were homogenized in 6 mL of 50 mmol/L phosphate
buffer (pH 7.8) and the supernatant after centrifugation
(10 000 r/min for 15 min at 4 ℃) was collected as enzyme
extracts. The reaction mixture (3.3 mL), which contained
2.4 mL of 65 mmol/L sodium phosphate buffer (pH 7.8),
0.2 mL of 13 mmol/L methionine, 0.2 mL of 75 nmol/L
nitroblue tetrazolium (NBT), 0.2 mL of 10 μmol/L EDTA,
0.2 mL of 2 μmol/L riboflavin and 0.1 mL of the enzyme
extract, was illuminated by light (60 mol/(m2·s)) for 30 min,
and the absorbance was then determined at 560 nm. Identical
solutions held in dark served as the blank. SOD activity
was expressed as U/(h·g), where one unit was defined as
the amount of enzyme that caused a 50% decrease of SOD-
inhibited NBT reduction per mass of fresh fruit flesh.
1.3 Statistica l analysis
A completely randomized design was used for this
study, and the analysis was carried out in triplicate. The data
were expressed as means ± standard deviation. An ANOVA
test (using SAS 9.0 statistical software) was used. Signifi cant
differences between the means of parameters were determined
using the LSD test at 5% level.
2 Results and Analysis
2.1 Effect of PA on decay
Research shown that, low temperature[9], coating[17] or
the packing[18] could be effective in reducing decay incidence.
The decay indices of all Gynura leaves during storage
increased consistently, which were significantly inhibited by
PA (Fig. 1a). The similar effects of PA on Chrysanthemum
nankingense[19] indicate PA can inhibit the decay of leafy
vegetables. Besides, 0.5 mmol/L PA, which reduced the
decay index of Gynura leaves most effectively from 10%
(control) to 5% on day 15 with significant difference, is
much higher than the optimum concentration (0.1%) reported
previously[19], suggesting that the inhibited decay of leafy
vegetables may be related to PA concentration.
a
a
a
b
b
b
d
d
d
c
c
c
0
2
4
6
8
10
12
0 5 10 15
Storage time/d
D
ec
ay
in
de
x/
%
control 0.1 mmol/L PA
0.5 mmol/L PA 1.0 mmol/L PA
a
0
50
100
150
200
250
300
0 5 10 15
Storage time/dR
es
pi
ra
tio
n
ra
te
/(C
O
2 n
m
ol
/k
g)
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
b
Fig. 1 Effects of PA pretreatment on decay index (a) and respiration
rate (b) of Gynura bicolor D.C leaves during storage at 0 ℃. Values are
the means ± SE of triplicate assays. Vertical bars represent the standard
errors of the means
2.2 Effect of PA on respiration rate
Respiratory rate changes of Gynura during storage
at 0 ℃ are shown in Fig. 1b. The respiratory rates of all 4
※包装贮运 食品科学 2014, Vol.35, No.02 319
treatments rose consistently with largest elevation for control
and smallest for PA treatments, and there were significant
differences between the PA treatments. The results reveal that
0.5 mmol/L PA affected Gynura respiratory inhibition more
evidently than others.
2.3 Effect of PA on production of O2
－·, MDA and
relative leakage rate
O2
－· production in Gynura leaves all decreased within
the first 5 days, increased during the next 5 days and reduced
thereafter (Fig. 2a). Significantly less O2
－· was produced in
the Gynura leaves treated with PA than that in control, and
minimum O2
－·was produced 15 days after 0.5 mmol/L PA
treatment with significant difference (P＜0.05). The results
are similar to the influences of 0.1% PA on Chrysanthemum
nankingense[19]. Since the level of O2
－· produced during
bioprocesses indicates velocity, lower O2
－· production based
on postharvest PA means slower quality loss and longer
storage life of Gynura leaves.
a
0
200
400
600
800
1 000
1 200
1 400
0 5 10 15
Storage time/d
O
2－
g
c
on
te
nt
/ (m
m
ol
/g
)
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
b
8
10
12
14
0 5 10 15
Storage time/d
M
D
A
c
on
te
nt
/(n
mo
l/g
)
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
c
0
10
20
30
40
50
0 5 10 15
Storage time/d
R
el
at
iv
e
le
ak
ag
e
ra
te
/%
Fig. 2 Effects of PA pretreatment on the levels of superoxide anion radicals (a)
and malondialdehyde (b), and relative leakage rate (c) in Gynura bicolor D.C
leaves during storage at 0 ℃. Values are the means ± SE of triplicate assays.
Vertical bars represent the standard errors of the means
The MDA levels in Gynura leaves during storage at
0 ℃ are shown in Fig. 2b. MDA production in all leaves
gradually decreased within the first 10 days and changed
slightly thereafter. Notably, the MDA values were lower
in all PA-treated Gynura leaves than that in control at the
same determined time. Since MDA is the product of lipid
peroxidation that results in the leakage of cells, the above
results show that lipid oxidation was inhibited maximally by
0.5 mmol/L PA (P＜0.05).
Relative leakage represents the vigor of plant tissues
or cells. As shown in Fig. 2c, the relative leakage rates of all
treated Gynura leaves decreased within the first 5 days and then
gradually increased. The decrease of relative leakage rate may
be attributed to the transfer of Gynura leaves harvested from
trees that were then stored under cold condition (0 ± 1) ℃.
Fig. 1b exhibits that Gynura leaves treated with PA were less
prone to relative leakage than control, and 0.5 mmol/L PA
treatment with minimum relative leakage reached significant
difference (P＜0.05). The results suggest that PA managed
to slow down the changes of cell relative leakage and to
postpone the senescence of tissues.
2.4 Effect of PA on PPO, POD, SOD and CAT activity
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
a
4 000
6 000
8 000
10 000
12 000
0 5 10 15
Storage time/d
PP
O
a
ct
iv
ity
/(U
/(m
in
·
g))
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
b
0
5 000
10 000
15 000
20 000
25 000
0 5 10 15
Storage time/d
PO
D
a
ct
iv
ity
/(U
/(m
in
·
g))
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
0
1 000
2 000
3 000
4 000
5 000
0 5 10 15
Storage time/d
C
AT
a
ct
iv
ity
/(U
/(m
in
·
g)) c
320 2014, Vol.35, No.02 食品科学 ※包装贮运
control
0.1 mmol/L PA
0.5 mmol/L PA
1.0 mmol/L PA
d
120
140
160
180
200
220
240
0 5 10 15
Storage time/d
SO
D
a
ct
iv
ity
/(U
/(h
·
g))
Fig. 3 Effect of PA on the activities of polyphenoloxidase (a),
peroxidase (b), catalase (c), and superoxide dismutase (d) in Gynura
leaves during storage at 0 ℃. Values are the means ± SE of triplicate
assays. Vertical bars represent the standard errors of the means
PPO activities of PA-treated and CK Gynura leaves
remained almost constant over the first 5 days, and increased
slightly afterwards, with lowest PPO activity after 0.5 mmol/L
PA treatment (P＜0.05) (Fig. 3a). The results are also
consistent with the impact of PA on Chrysanthemum
nankingense[19]. All these suggest that PA can regulate the
PPO activity and then affect the color changes (normally
browning and dull) of leaves.
As a crucial enzyme of plants, POD can reduce H2O2
with a variety of co-reducing agents available in cells. The
changing model of POD activity was similar in all treatments
(Fig. 3b). POD activity of Gynura leaves treated with
0.5 mmol/L PA changed significantly differently from those
of other treatments (P＜0.05) during 15 days of storage, from
2.47×103 U/(min·g) on Day 5 to 15.34×103 U/ (min·g) on
Day 15.
Although the CAT activities of PA-treated Gynura
leaves all gradually decreased during 15 days of storage
(Fig. 3c), the activity of 0.5 mmol/L PA-treated Gynura
leaves was significantly higher, inferring that PA at
suitable concentration can continuously deactivate oxygen
efficiently in Gynura leaves without undesirable damages to
cells/tissues.
SOD activities of Gynura leaves were continuously
lowered throughout storage (Fig. 3d) from 201.2 U/(h·g) at
harvest to 151.4 U/(h·g) for control, 168.3 U/(h·g) for 0.1
mmol/L PA, 177.8 U/(h·g) for 0.5 mmol/L PA and 165.3 U/
(h·g) for 1.0 mmol/L PA on Day 15. Compared with control,
treatments with PA, especially with 0.5 mmol/L PA, significantly
reduced the loss of SOD activity during storage (P＜0.05).
The above results suggest that PA can keep significantly
stronger antioxidation capability of treated Gynura leaves.
Although antioxidative activity decreased during storage,
the enhanced system delayed the senescence of harvested
leaves[20]. Further studies, such as the indirect or/and direct
effects of PA on postponed Gynura leafy senescence during
storage, are still in need.
3 Discussion
3.1 Effects of PA on decay of gynura leaf during cold storage
Decay of vegetable, including browning, yellowing
and putrescence, often leads to quality loss, being
predominantly responsible for its short shelf-life and
unfavorable marketability[21]. In this research, browning
played an important role in quality loss and limited Gynura
storage life. The decay values of all PA-treated Gynura
leaves were lower than that of control during storage with 0.5
mmol/L PA-treated ones being minimum (P＜0.05). The
results support an earlier study that suitable exogenous
application of phytochemicals (e.g. salicylic acid) boosted
eating quality, for instance, by inhibiting browning and
effectively maintaining eating quality of Chinese water
chestnut[22]. In this study, PPO activity was significantly
inhibited and increased by 0.5 mmol/L and 1.0 mmol/L
PA respectively. Similar to the results of Zhao Yonggan
et al.[19], we found that excess (higher concentration than
necessary) PA may conversely accelerate decay. The
negative correlation between PPO activity and decay index
(P＜0.05) indicates that PA delayed the decay of Gynura
by low-level PPO. However, PA at higher concentration
was not suitable for inhibiting PPO activity.
3.2 Effects of PA on antioxidant enzymes in relation to
postponed senescence of gynura leaves during storage
In higher plants, senescence is characterized by
breakdown of cell wall components and membrane disruption
resulting in cellular decompartmentation and loss of tissue
structure, all the characteristics of which originate from active
oxygen accumulation. Antioxidant enzymes such as SOD,
POD and CAT are critical in antioxidant defense while being
involved in tissue browning during the storage of leaves[23].
SOD converts O2
－· to H2O2 that can be further scavenged
by CAT and POD. Lacan et al.[24] have reported that high
SOD/CAT ratio delayed the senescence of muskmelon
(cv. Clipper) during storage. In this study, 0.5 mmol/L PA
apparently increased the activities of SOD and POD, and
retarded O2
－· accumulation and MDA production. The
results indicate that under 0.5 mmol/L PA stress, O2
－·
and MDA hardly accumulated, and antioxidant enzymes
such as SOD and POD were subject to being activated,
which eliminated endogenous active oxygen efficiently and
※包装贮运 食品科学 2014, Vol.35, No.02 321
thus reduced membrane-lipid peroxidation. Therefore, 0.5 mmol/L
PA maintained the membrane integrity and delayed the decay
of Gynura leaves during storage at low temperature (0 ℃), which
significantly lowered the relative leakage rate of Gynura
leaves with PA treatments.
3.3 Hypothetical model of PA action
In the present study, PA may delay the senescence
of Gynura leaves by disrupting membrane transport and
permeability. Plants respond to environmental stress
following a complex paradigm. The hypothetical model of
salicylic acid action on environmental stress responses was
described as inhibition of the H2O2-degrading activity of
CAT, which is in accordance with the results herein. Hence,
we also ascribed the Gynura responses to senescence stress
to inhibited H2O2-degrading activity of CAT by PA
[25], thus
increasing the accumulation of endogenous H2O2 from
which other reactive oxygen species may activate and
strengthen the expression of plant defense-related genes as
second messengers. Nevertheless, mechanisms regarding the
transformation of H2O2 and other derivative reactive oxygen
species are required to verify our hypothesis.
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