EAEF 13 (4) : 98-104, 2020 Research Article Impact of Electric Field on Physicochemical Properties and Antioxidant Activity of Persimmon (Diospyros kaki L.) Naruesorn JAISUE 1, 2 , Sutthiwal SETHA 1, 2 , Daisuke HAMANAKA 3 , Matchima NARADISORN 1, 2 * Abstract The aim of this study was to investigate the effect of electric field on physicochemical properties and antioxidant activity of persimmon (Diospyros kaki L.). Persimmons were exposed to electric field strength of 7 kV / cm for 3, 6 or 9 d during 15 d of storage at 10 ℃. Persimmons without electric field treatment was considered as a control. The results showed that fruits received electric field for 9 d remained firmer, contained higher total phenolic content and had higher antioxidant activity than the untreated control after storage for 15 d. This suggests that exposure to electric field during storage may be useful for prolonging the shelf life of persimmon; and for producing and preserving persimmon product with high total phenolic content and antioxidant capacity. [Keywords] electric field, non-thermal technology, persimmon, total phenolic content, antioxidant activity I Introduction Persimmons (Diospyros kaki L.) are climacteric fruit that differ from other climacteric fruit in which persimmons pro- duce a low amount of ethylene at mature stage (Ramin, 2008). Persimmon fruit rapidly soften when the climacteric stage begins; consequently, they become unmarketable within a few days due to its jelly-like flesh (Ramin, 2008). Rapid softening after harvest is the limitation for storage and distribution of persimmons. Several attempts have been made to reduce respiration rate, extend shelf life, maintain quality and im- prove bioactive compounds in persimmons, e.g., the use of CO2 (Min et al., 2018), 1-MCP (Luo, 2007; Min et al., 2018), calcium lactate in combination with hot water treatment (Naser et al., 2018) and high electric field (HEF) (Liu et al., 2017). Electric field technology is a non-thermal preservation method (Atungulu et al., 2005; Dalvi-Isfahan et al., 2016), which has been investigated as alternative means for pre- serving quality of agricultural produce and food product. The high voltage electric field has showed its potential application in food processing efficiency; for example, increase food dehydration or drying and improve juice yield and polyphenol extraction in apricot, orange, pomelo and lemon (Dalvi-Isfahan et al., 2016). In wine making, the high electric field was applied to inactivate microorganisms before bottling and im- prove wine quality; however, it degraded phenolic compounds and modified the physicochemical composition of wine (Zeng et al., 2008). There have been some reports on the effect of electric field on texture of some fruits and vegetable, such as carrots, potatoes and apples, and with high intensity of electric field, it causes loss of turgor and collapse of cell membranes (González-Casado et al., 2018; Kharel et al., 1996; Lebovka et al., 2004; Puértolas et al., 2017). However, the application of high electric field (430 kV / m) treatment during preclimacteric period suppressed the respiration rate of pears, plums and bananas; and delayed ripening in banana and sweet peppers (Kharel et al., 1996). In addition, electric field may act as abiotic stress that induces the production and accumulation of secondary metabolites involved in defence mechanisms in plants (González-Casado et al., 2018). The objective of this study was to investigate the effect of electric field on physicochemical properties and antioxidant activity of persimmon. II Materials and Methods 1. Persimmon fruit Persimmon fruit at commercial stage (mature and deep yellow colour) with a good quality and uniform size were purchased from a local market in Kagoshima, Japan and treated on the day of purchase. 2. Electric field treatment The electric field generating device was set up in the labo- ratory using a refrigerator (KuraBan KB-120F-IF4D, MARS 1 School of Agro-Industry, Mae Fah Luang University, Thailand 2 Research Group of Postharvest Technology, Mae Fah Luang University, Thailand 3 Faculty of Agriculture, Kagoshima University, Japan * Corresponding author: [email protected]
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EAEF 13 (4) : 98-104, 2020 Research Article
Impact of Electric Field on Physicochemical Properties and
Antioxidant Activity of Persimmon (Diospyros kaki L.)
The aim of this study was to investigate the effect of electric field on physicochemical properties and antioxidant
activity of persimmon (Diospyros kaki L.). Persimmons were exposed to electric field strength of 7 kV / cm for 3, 6 or 9 d
during 15 d of storage at 10 ℃. Persimmons without electric field treatment was considered as a control. The results
showed that fruits received electric field for 9 d remained firmer, contained higher total phenolic content and had higher
antioxidant activity than the untreated control after storage for 15 d. This suggests that exposure to electric field during
storage may be useful for prolonging the shelf life of persimmon; and for producing and preserving persimmon product
with high total phenolic content and antioxidant capacity.
[Keywords] electric field, non-thermal technology, persimmon, total phenolic content, antioxidant activity
I Introduction
Persimmons (Diospyros kaki L.) are climacteric fruit that
differ from other climacteric fruit in which persimmons pro-
duce a low amount of ethylene at mature stage (Ramin, 2008).
Persimmon fruit rapidly soften when the climacteric stage
begins; consequently, they become unmarketable within a few
days due to its jelly-like flesh (Ramin, 2008). Rapid softening
after harvest is the limitation for storage and distribution of
persimmons. Several attempts have been made to reduce
respiration rate, extend shelf life, maintain quality and im-
prove bioactive compounds in persimmons, e.g., the use of
CO2 (Min et al., 2018), 1-MCP (Luo, 2007; Min et al., 2018),
calcium lactate in combination with hot water treatment (Naser
et al., 2018) and high electric field (HEF) (Liu et al., 2017).
Electric field technology is a non-thermal preservation
method (Atungulu et al., 2005; Dalvi-Isfahan et al., 2016),
which has been investigated as alternative means for pre-
serving quality of agricultural produce and food product. The
high voltage electric field has showed its potential application
in food processing efficiency; for example, increase food
dehydration or drying and improve juice yield and polyphenol
extraction in apricot, orange, pomelo and lemon (Dalvi-Isfahan
et al., 2016). In wine making, the high electric field was
applied to inactivate microorganisms before bottling and im-
prove wine quality; however, it degraded phenolic compounds
and modified the physicochemical composition of wine (Zeng
et al., 2008). There have been some reports on the effect of
electric field on texture of some fruits and vegetable, such as
carrots, potatoes and apples, and with high intensity of
electric field, it causes loss of turgor and collapse of cell
membranes (González-Casado et al., 2018; Kharel et al.,
1996; Lebovka et al., 2004; Puértolas et al., 2017). However,
the application of high electric field (430 kV / m) treatment
during preclimacteric period suppressed the respiration rate of
pears, plums and bananas; and delayed ripening in banana and
sweet peppers (Kharel et al., 1996). In addition, electric field
may act as abiotic stress that induces the production and
accumulation of secondary metabolites involved in defence
mechanisms in plants (González-Casado et al., 2018). The
objective of this study was to investigate the effect of electric
field on physicochemical properties and antioxidant activity
of persimmon.
II Materials and Methods
1. Persimmon fruit
Persimmon fruit at commercial stage (mature and deep
yellow colour) with a good quality and uniform size were
purchased from a local market in Kagoshima, Japan and
treated on the day of purchase.
2. Electric field treatment
The electric field generating device was set up in the labo-
ratory using a refrigerator (KuraBan KB-120F-IF4D, MARS
1 School of Agro-Industry, Mae Fah Luang University, Thailand 2 Research Group of Postharvest Technology, Mae Fah Luang University, Thailand 3 Faculty of Agriculture, Kagoshima University, Japan * Corresponding author: [email protected]
JAISUE, SETHA, HAMANAKA, NARADISORN : Impact of Electric Field on Physicochemical Properties
and Antioxidant Activity of Persimmon (Diospyros kaki L.) 99
Company, Japan) equipped with electrode plates. The
schematic diagram of the device is shown in Fig. 1. Fruits
were divided into four groups based on electric field
treatments: 1) control (no electric field treatment); 2) 3-day
electric field treatment; 3) 6-day electric field treatment and
4) 9-day electric field treatment. For electric field treatment,
fruit were treated with electric field strength of 7 kV / cm for
either 3, 6 or 9 d during 15 d of storage at 10 ℃. The whole
experiment was conducted at 10 ℃ and 85 ± 5 % relative
humidity. Quality assessment was conducted every 3 d during
storage. There were 10 fruits per treatment for each assess-
ment.
3. Weight loss
Persimmon fruit were weighed using a digital balance
(PB3002-S / FACT, Mettler Toledo Inc., USA) before and
after the storage period to calculate percentage of fresh weight
loss as:
𝑊𝐿𝐼𝑊 𝐹𝑊
𝐼𝑊100 1
where, WL is the weight loss (%), IW is the initial weight (g)
of persimmon and FW is the final weight (g) of persimmon on
sampling date.
4. Firmness
Fruit firmness was determined at four different locations on
fruit using a Creep Meter RE2–3305C (YAMADEN Co. Ltd.,
Japan) with 4 mm diameter tip and expressed in N.
5. CO2 production
CO2 production was measured by sampling 1 mL of two
persimmons incubated for 2 h in a sealed barrier film bag
(Vinyl Alcohol-Based Polymeric Film, AS ONE Corp., Japan).
CO2 production (mL / kg h) was measured on a gas chroma-
tography (GC-8 A, SHIMADZU Corp., Japan).
6. Total soluble solids content
Total soluble solids (TSS) content was determined by using
a hand-held digital refractometer (PAL-BX / Acid F5, ATAGO
Co. Ltd., Japan) and expressed as degree Brix (°Brix).
7. Colour
Peel colour was determined using a colorimeter (COLOR
READER CR-10 Plus, KONICA MINOLTA Inc., Japan).
Readings were taken at four random locations on each fruit
and recorded in L* (brightness), a* (red) and b* (yellow)
units. The hue angle h (°) was calculated according to the
equation:
ℎ tan𝑏∗
𝑎∗ 2
8. Total phenolic content analysis
Total phenolic content (TPC) was determined by following
the Folin–Ciocalteu method (ISO 14502–1, 2005). An aliquot
of persimmon extract (500 μL) was diluted with distilled
water (500 μL). Then, 200 μL of the solution was added to a
test tube and mixed with 1,000 μL of 10 % v / v Folin-Ciocalteu
phenol’s reagent and 800 μL of sodium carbonate solution.
After 1 h of incubation at ambient temperature, the absor-
bance was measured at 765 nm with a spectrophotometer
(U-2900, Hitachi High-Tech Science Corp., Japan). The TPC
was calculated and expressed as mg gallic acid equivalent
(GAE) per 100 g fresh weight (FW).
9. Antioxidant activity analysis
The antioxidant radical scavenging of persimmon extract
was measured using the DPPH (2,2-diphenyl-1-picrylhydrazyl)
nitrogen free radical according to the method of Molyneux
(2004). Persimmon extract (200 μL) was diluted with distilled
water (200 μL), then 50 μL of the solution was mixed with
1950 μL of DPPH solution and kept in the dark condition for
30 min. The absorbance was measured at 517 nm with a
spectrophotometer. Trolox was used as a standard and the
results were expressed as μmol trolox equivalent (TE) per
100 g fresh weight (FW).
The Ferric Reducing Antioxidant Power (FRAP) assay was
determined according to the method of Benzie and Szeto
(1999). FRAP solution was prepared by mixing 300 mM
Fig. 1 Schematic diagram of equipment installation
100 Engineering in Agriculture, Environment and Food Vol. 13, No. 4 (2020)
acetate buffer (pH 3.6), 10 mM TPTZ in 40 mM HCl and
20 mM FeCl3 in a ratio of 10 : 1 : 1 (v / v / v). Persimmon
extract (250 mL) was diluted with distilled water (4,750 mL),
400 μL of the solution was then mixed with 2.6 mL of FRAP
solution and incubated at 37 ℃ in water bath (Personal-11,
TAITEC Corp., Japan) for 30 min. The absorbance was
measured at 595 nm with a spectrophotometer. Ferrous sulfate
was used as standard and the results were expressed as μmol
Fe(ll) per 100 g fresh weight (FW).
10. Statistical analysis
Data were subjected to statistical analysis using SPSS
software version 20. The significant differences among the
treatments were compared using analysis of variance (ANOVA)
followed by Duncan’s multiple range method. Differences
were considered significant at p < 0.05.
III Results and Discussion
1. Weight loss
An increase in weight loss during storage was observed in
both untreated and electric field treated fruit (Fig. 2). Similar
to previous reports, the use of electric field with high voltage
did not affect weight loss in apple, pear, plum, banana and
sweet pepper (Kharel et al., 1996). Weight loss during storage
may be possibly due to an increase in moisture loss from fruit
caused by transpiration and respiration. In this study, the
weight loss was not due to respiration activity as there was no
difference in CO2 production among electric field and
non-electric field treatments during storage at 10 ℃ (Table 1).
2. Fruit firmness
Fruit firmness in all treatments decreased continuously over
the storage period of 15 d (Fig. 3). After 12 and 15 d of storage,
fruit firmness was higher in persimmon fruits treated with
electric field for 9 d compared with the untreated control. This
result was contrary to the other reports in which electric field
treatment causing tissue softening as a consequence of cell
membrane permeabilisation induced by the electric field. The
application of pulsed electric field resulted in loss of turgor
and rupture of cell membranes in apple (Lebovka et al., 2004)
and reduction in firmness values in tomato (González- Casado
et al., 2018). However, the higher firmness following electric
field treatment obtained in this study was probably due to the
membrane recovery after the treatment which is called revers-
ible electroporation. Depending on the electric field treatment
intensity, the membrane can recover its integrity and structure
once the electric field treatment has finished (Puértolas et al.,
2017) and this possibly results in firmer tissues.
3. CO2 production
The effect of electric field on CO2 production of per-
simmon fruits is shown in Table 1. The electric field of 7 kV /
Each bar represents the mean from n = 10. Vertical bars
represent the standard deviation (SD) of the mean.
Fig. 2 Effect of electric field (EF) on weight loss in persim-
mon during storage at 10 ℃
Table 1 Effect of electric field (EF) on CO2 production by
persimmons during storage at 10 ℃
Days of Storage CO2 production (mL / kg / h)
Control EF treatment
0 16.14 ± 5.90
3 0.41 ± 0.17a 0.18 ± 0.14a
6 5.59 ± 1.48a 6.27 ± 0.13a
9 2.84 ± 0.58b 4.84 ± 0.14a
12 0.94 ± 0.23a 1.61 ± 1.03a
15 2.95 ± 0.24b 4.52 ± 0.61a
Data shown are mean ± SD. Different letters in the same row
indicate statistically significant differences (p < 0.05) among
treatments in the same storage period.
Each bar represents the mean from n = 10. Vertical bars
represent the standard deviation (SD) of the mean. Fig. 3 Effect of electric field (EF) on fruit firmness of persim-
mon during storage at 10 ℃
JAISUE, SETHA, HAMANAKA, NARADISORN : Impact of Electric Field on Physicochemical Properties
and Antioxidant Activity of Persimmon (Diospyros kaki L.) 101
cm did not influence respiration rate of persimmon fruits as
no difference in CO2 production between the treatments,
except those in Day 9 and Day 15 of storage. Persimmons
treated with electric field generally had a higher CO2 pro-
duction than the controls; however, there was no increase in
CO2 production in both treatments during storage at 10 ℃ for
15 d, compared with the initial day. In contrast, CO2
production markedly increased in tomato (González-Casado
et al., 2018) and fresh-cut apples (Dellarosa et al., 2016)
following application of electric field. However, the decrease
of CO2 production may occur as a consequence of a severe
loss of cell viability due to high intensity of electric field
(Dellarosa et al., 2016).
4. Colour
Persimmon fruit ripening shows a characteristic change in
skin colour from yellow to deep yellow or yellow-red during
ripening. Fig. 4 shows the effect of electric field treatment on
persimmon peel colour assessed by using the CIELAB colour
space. There was no difference in a* and b* values between
the fruits in electric field treatment and control. Peel lightness
as indicated by L* value decreased during storage in all
treatments with no difference among the treatments. Similarly,
a reduction of hue angle values during storage was observed
in all treatments, representing the colour changes from the
green region to yellow and red. However, the peel of un-
treated fruit (47.93 ± 4.92) had a lower hue angle compared to
electric field-treated fruit for 9 d (52.14 ± 2.72) after storage
for 15 d, where the low hue angle value indicated less green
(yellow) skin. This result suggested that the 9-day electric
field treatment could possibly delay ripening of persimmons
by preserving their green colour. This observation was in ac-
cordance with the result obtained in fruit firmness in which
the 9-day electric field fruits remained firmer than the control,
where the firmness decreased as the degree of ripening increased.
5. Total soluble solids
Total soluble solids (TSS) value is an important parameter
that influences the flavour of fruit. In general, TSS increases
with the advancement of ripening process and storage period.
Fig. 5 shows that TSS of persimmon fruit in all treatments did
not change over time in storage at 10 ℃. After 15 d of storage,
fruits treated with electric field for 3, 6 or 9 d (15.9 ± 0.21,
14.8 ± 0.10, 15.6 ± 0.15 °Brix, respectively) showed similar
TSS values with respect to value of the control (15.7 ±
0.10 °Brix). This result suggested that TSS content was not
influenced by electric field.
6. Total phenolic content
Total phenolic content of persimmon fruit was higher in
Vertical bars represent the standard deviation (SD) of the mean from n = 10. Fig. 4 Effect of electric field (EF) on lightness, a*, b* and Hue angle of persimmon peel colour during storage at 10 ℃
(a) Lightness
(b) a*
(c) b*
(d) Hue angle
102 Engineering in Agriculture, Environment and Food Vol. 13, No. 4 (2020)
peel than in pulp and was affected by electric field treatment
(Fig. 6). At the end of storage duration of 15 d, electric field
treatment for 9 d significantly increased (p < 0.05) total
phenolic content in pulp and peel by 55.76 and 41.09 %,
respectively, in comparison to the control (non-electric field
treatment). In pulp, electric field treatment increased total
phenolic content of persimmon from 184.01 ± 5.46 mg GAE /
100 g FW (control) to 286.62 ± 5.79 mg GAE / 100 g FW
(9-day electric field treatment). Similar result was obtained by
Shivashankara et al. (2004) in which high electric field
increased total phenolic content in ripe mangoes. An increase
in total phenolic content in electric field treatment is probably
due to the response of plants to stress induced by electric field.
However, many studied suggested that electric field may
inactivate enzymes, such as polyphenol oxidase (PPO) and
peroxidase (POD), which involve in phenolic compound
oxidation; hence, phenolic compounds may be preserved
(Dziadek et al., 2019). Correspondingly, the use of pulses
having high electric field for a few μs to ms led to increase in
total phenolic content in various fruit products, e.g., plum and
grape peels (Medina-Meza and Barbosa-Cánovas, 2015),
grape juice (Leong et al., 2016) and orange peel (El Kantar et
al., 2018; Luengo et al., 2013). However, pulsed electric field
treatment did not affect the content of total polyphenols in
tomato juice (Odriozola-Serrano et al., 2009) and apple juice
(Dziadek et al., 2019).
7. Antioxidant activity
Antioxidant activity of persimmon was evaluated in pulp
and peel by DPPH (Fig. 7) and FRAP (Fig. 8) scavenging
ability. The DDPH radical scavenging ability of persimmons
treated with electric field for 3 and 9 d increased compared to
untreated persimmons. In pulp, at the end of storage duration
(15 d), antioxidant activity measured by DPPH radical scav-
enging ability of fruit in 9-day electric field treatment (101.23
± 1.43 μmol TE / 100 g FW) was 44.42 % higher than that in
the control (56.26 ± 1.80 μmol TE / 100 g FW). Similar result
was obtained in peel where DPPH increased by 45.74 and
23.62 % in 3-day electric field treatment (75.36 ± 5.69 μmol
TE / 100 g FW) and 9-day electric field treatment (53.54 ±
10.96 μmol TE / 100 g FW), respectively, in comparison to
untreated control (40.89 ± 8.43 μmol TE / 100 g FW). Likewise,
FRAP scavenging ability in persimmon pulp and peel treated
with electric field for 3 and 9 d was significantly higher (p <
0.05) than that in the control at the end of storage of 15 d. In
addition, the FRAP values was double in electric field treatment
compared to the control. The result suggested that application
of electric field treatment enhanced antioxidant activity in
persimmons. This result is similar to those obtained by Jeya
Shree et al. (2018) for grape extract and Rodríguez-Roque et
al. (2015) for blueberry; their findings were that the use of
short electricity pulses improved antioxidant activity in such
fruit. One of the explanations for this phenomenon is that the
accumulation of antioxidants may be due to the contribution
Each bar represents the mean from n = 10. Vertical bars
represent the standard deviation (SD) of the mean. Fig. 5 Effect of electric field (EF) on total soluble solids
content in persimmon during storage at 10 ℃
Each bar represents the mean from n = 10. Vertical bars
represent the standard deviation (SD) of the mean.
Fig. 6 Effect of electric field (EF) on total phenolic content
in persimmon pulp and peel during storage at 10 ℃
(a) Persimmon pulp
(b) Persimmon peel
JAISUE, SETHA, HAMANAKA, NARADISORN : Impact of Electric Field on Physicochemical Properties
and Antioxidant Activity of Persimmon (Diospyros kaki L.) 103
of total phenolic content, which is either greatly produced in
response to physical stress caused by electric field or pre-
served due to inactivation of enzyme involving in phenolic
compound oxidation by electric field (Dziadek et al., 2019).
Ertugay et al. (2013) reported that pulsed electric field at 100
or more pulses at 40 kV / cm completely inactivated poly-
phenol oxidase (PPO) activity in apple juice.
IV Conclusions
The results of this study demonstrate that electric field
treatment at the strength of 7 kV / cm led to an increase in
total phenolic compound content and antioxidant activity of
persimmon. The exposure to electric field did not cause major
changes in weight loss, firmness and peel colour. These
findings suggest that application of electric field strength
during storage may be useful for enhancing total phenolic
content and antioxidant capacity of persimmon and this would
meet consumer demand for healthy fruit and food products. In
addition, the mechanism of how electric field induces total
phenolic content and antioxidants may be of interest for
further investigation.
Acknowledgment
The authors acknowledge Kagoshima University, Japan and
Mae Fah Luang University, Thailand for supporting this
research project. Thanks to Fujimura Miki for providing a
schematic diagram of an electric field generator.
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