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*Manuscript
Click here to view linked References
Bioactive components analysis of two various gingers (Zingiber officinale
Roscoe) and antioxidant effect of ginger extracts
Hsiang-Yu Yeh b,*, Cheng-hung Chuang b, Hsin-chun Chen c, Chu-jen Wan d, Tai-liang
Chen a, Li-yun Lin a,*
a
Department of Food Science and Technology, Hungkuang University, 34 Chung-Chie
Road, Shalu, Taichung 43302, Taiwan
b
Department of Nutrition, Hungkuang University, 34 Chung-Chie Road, Shalu, Taichung
43302, Taiwan
c
Department of Cosmeceutics, China Medical University, 91 Hsueh-Shih Road, Taichung
433, Taiwan
d
Department of Dietetics, Tachia General Lee hospital, Taichung, Taiwan
* To whom correspondence should be addressed.
Dr. Hsiang-Yu Yeh
Department of Nutrition, Hungkuang University,
34 Chung-Chie Road, Shalu, Taichung 43302, Taiwan
Telephone: +886-4-26318652 Ex. 5037
Fax: +886-4-2631-4944
E-mail address: hyyeh@sunrise.hk.edu.tw
Dr. Li-Yun Lin
Department of Food Science and Technology,, Hungkuang
University, 34 Chung-Chie Road, Shalu, Taichung 43302,
Taiwan
Telephone: +886-4-26318652 Ex. 5043
Fax: +886-4-2633-4944
E-mail address: lylin @sunrise.hk.edu.tw
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ABSTRACT
Ginger, a medicinal herb with bioactive components, is now widely used. This study
reports the information of bioactive components in two varieties ginger root (Zingiber
officinale Roscoe), Guangdong ginger (GG) and Chu-ginger (CG) available in Taiwan
and compares their bioactive components and antioxidant properties using aqueous and
ethanolic extract. The proximate analysis of both ginger rhizomes gave similar profiles.
Total contents of organic acids were 37.33 and 91.06 mg/g dry weight for GG and CG,
respectively, with oxalic and tartaric acids being two major acids. HPLC analysis
revealed gingerols
and shogaol in both ginger were similar but curcumin content was higher in GG. The
essential oils exhibited similar volatile profiles and 60 and 65 compounds were
identified for GG and CG, respectively. Among the essential oils major components
were camphene, sabinene,α-curcumene, zingiberene, α-farnesene, βsesquiphellandrene, neral, and geranial. The antioxidant effect of ginger ethanolic
extracts were more effective than aqueous extracts in Trolox equivalent antioxidant
capacity and Ferric reducing ability of plasma. Contrarily, ginger aqueous extracts
were more effective in free radical scavenging
activities and chelating abilities. Based on the results, two ginger rhizomes exerted
protective effects and could be used as a flavouring agent and a natural antioxidant.
Keywords: ginger rhizome; composition; volatile component; antioxidant property
1. Practical application
Ginger, the rhizome of Zingiber officinale Roscoe is commonly used as a spice,
dietary supplement and medicine. is found to be effective in antioxidant, antiinflammatory and antimicrobial activities. Currently, two varieties of ginger rhizomes,
Guangdong-ginger and Chu-ginger, are available in Taiwan and found to be
comparable in carbohydrate, fat and fibre contents. Oxalic and tartaric acids were two
major acids. Gingerols, shogaol and curcumin were their active components. The
essential oils of two gingers exhibited similar volatile profiles and 60-65 compounds
were identified. Ethanolic extracts were more effective than aqueous extracts in Trolox
equivalent antioxidant capacity and Ferric reducing ability of plasma whereas aqueous
extracts were more effective in scavenging and chelating abilities. However, both
extracts were effective in antioxidant properties assayed. Based on the results obtained,
two ginger rhizomes could be used as a flavouring agent and an antioxidant.
2. Introduction
Ginger, originated in the Indo-Malayan region, is now widely distributed across the
tropics of Asia, Africa, America and Australia. Ginger is the rhizome of Zingiber
officinale Roscoe belonging to family Zingiberaceae, commonly used as a spice for
over 2000 years (Bartley & Jacobs, 2000) and contains characteristic odour and flavour
such as the pungent taste (Jolad, Lantz, Chen, Bates, & Timmermann, 2005). The root
extracts contain compounds (6-gingerol and its derivatives), which have a high
antioxidant activity (Chen, Kuo, Wu, & Ho, 1986; Herrmann, 1994). In the animal
models, gingerols are bioactive components and could increase the motility of the
gastrointestinal tract and have analgesic, sedative, antipyretic and antibacterial
properties (O’hara, Kiefer, Farrell, & Kemper, 1998). Concomitant dietary feeding of
ginger significantly attenuated malathion induced lipid peroxidation and oxidative
stress in rats (Ahmed, Vandana, Pasha, & Banerjee, 2000). Curcumin, an another active
component present in ginger, was found to be an antioxidant and anti-inflammatory
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agent and induced haem oxygenase-1 and protected endothelial cells against oxidative
stress (Motterlini, Foresti, Bassi, & Green, 2000). Overall, ginger components might be
effective in antioxidant, anti-inflammatory and antimicrobial activities (Dugasani et al.,
2009; Jolad et al., 2005; Park, Bae, & Lee, 2008).
The antioxidants inhibit the reactive oxygen species (ROS), which are capable of
causing damage to DNA, associated with carcinogenesis, coronary heart disease, and
many other health problems related to advancing age (Patel et al., 2000). Scavenging
agent also acts as inhibitors of free radical scavenging (Sherwin, 1972). In rat
experiment indicate extracts of red and white ginger protect the brain through their
antioxidant activity, Fe2 + chelating and OH_ scavenging ability and prevented
oxidative stress by dietary of ginger intake (Oboh, Akinyemi, & Ademiluyi, 2012).
Nowadays, natural antioxidants are important in the food industry because of their
healthy effects (Ibañez et al., 2003). Thus, their demand has increased for growing
interest in foods obtained from natural sources (Aruoma et al., 1995; Kim, Kim, Kim,
& Heo, 1997). The extract quality is greatly influenced by the extraction methodology
used and solvent extraction techniques. Several studies have shown that extraction
method can alter the antioxidant activity and total phenolic content in the extracts
(Chan, Lim, & Omar, 2007; Ding et al., 2012; Sikora, Cieslik, Leszcznska, FilipiakFlorkiewicz, & Pisulewski, 2008). Either Ginger ethanolic extracts inhibit tumour
promotion in SENCAR mice (Katiyar, Agarwal, & Mukhtar, 1996) or Ginger aqueous
extracts inhibits proliferation and angiogenesis of colonic adenocarcinoma cells
(Brown et al., 2009).
Currently, two varieties of ginger rhizomes (Fig. 1S, Supplementary Material),
Guangdong-ginger (GG) and Chuginger (CG), are available in Taiwan. However, the
information about their proximate composition, bioactive components are not known.
Therefore, the objectives of this research are to establish the basic information of these
two gingers, furthermore to compare their bioactive components in essential oil and
antioxidant properties using different extraction solvents.
3. Materials and Methods
3.1. Materials
Two varieties of ginger rhizomes, GG and CG, were obtained from Mingjian
Township, Nantou County, Taiwan. Fresh gingers werewashed and air-dried at 50 _C
for 18 h. Air-dried samples were then ground in an RT-34 pulverising machine (Rong
Tsong Precision Technology Co., Taichung, Taiwan), screened through a 0.6 mm sieve
and stored in a desiccator before use.
3.2. Proximate analysis
The proximate compositions of the two types of ginger samples, including moisture,
ash, fat, fibre and protein, were determined according to the methods of Association of
Official Analytical Chemists (AOAC, 1990). Moisture was determined by drying to a
constant weight at 105 ℃. The crude lipid content was determined by extracting the
sample with petroleum ether with a Soxhlet apparatus. The protein content was
determined by the micro-Kjeldahl method. The carbohydrate content (g/100 g) was
calculated by subtracting the contents of ash, fat, fibre and protein from total dry
weight. Moisture was presented based on fresh weight (g/100 g). Other contents were
presented based on dry weight (g/100 g).
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3.3. Determination of organic acids
Sample powder (500 mg) was extracted with 50 mL of 80 mL/100 mL aqueous
ethanol. This suspensionwas shaken for 45 min at room temperature and filtered
through Whatman No. 4 filter paper. The residue was re-extracted five times with
additional 25-mL portions of 80 mL/100 mL ethanol. The combined filtrate was then
rotary evaporated at 40 _C and redissolved in deionised water to a final volume of 10
mL. The aqueous extract was filtered using a 0.45-mm polyvinylidene fluoride
membrane filter (Millipore, Billerica, MA, USA) and analysed using high-performance
liquid chromatography (HPLC). The HPLC system consisted of a Hitachi L-2130
pump (Tokyo, Japan), a Rheodyne 7725i injector (Rohnert Park, CA, USA), a 20-mL
sample loop, a Hitachi L-2400 UV detector, and an RP-18 GP250
column (4.6 x 250 mm, Mightysil, Kanto Chemical Co., Tokyo, Japan). The mobile
phase was acetonitrile/deionised water, 75:25 (v/v), at a flow rate of 0.8 mL/min; and
UV detectionwas at 300 nm. Each organic acid was identified using the authentic
organic acid (all from SigmaeAldrich, St. Louis, MO, USA) and quantified by its
respective calibration curve.
3.4. Determination of gingerols, shogaols and curcumin
The extraction procedure prepared for gingerols, shogaols and curcumin analysis
was same. Sample powder (2 g) was extracted with 15 mL of 80 mL/100 mL aqueous
methanol at 4 ℃ with stirring for 24 h. After centrifugation at 3800 g for 30 min, the
residuewas re-extracted twice as described above. The combined supernatantwas rotary
evaporated at 40 ℃ and redissolved in deionised water to a final volume of 10 mL. The
aqueous extract was filtered and injected onto HPLC. Gingerols and shogaols were
analysed according to the method of Schwertner and Rios (2007); and curcumin was
determined using the method of Heath, Pruitt, Brenner, and Rock (2003). The HPLC
system was the same as for organic acid analysis but included a TSK-GEL ODS-100S
column (4.6 x 250 mm, 3 mm, Tosoh Co., Tokyo, Japan). The mobile phase for
gingerols and shogaols was methanol/water, 65:35 (v/v), at a flow rate of 1.0 mL/min;
and UV detection was at 282 nm. The mobile phase for curcumin was
acetonitrile/methanol/water/acetic acid, 41:23:35:1 (v/v/v/v), at a flow rate of 0.8
mL/min; and UV detection was at 422 nm. Each component was identified using the
authentic compound (all from SigmaeAldrich) and quantified by its respective
calibration curve.
3.5. Analysis of volatile components
Volatile components in ginger samples were isolated by the simultaneous steamdistillation and solvent-extraction (SDE) ethod using a Likens and Nickerson apparatus
(Likens & Nickerson, 1964) with some modification by Filek, Bergamini, and Lindner
(1995). Sample powder (150 g) was placed into the apparatus and deionised water
(1500 mL) was added. The solvent mixture (50 mL) of n-pentane and diethyl ether
(column distilled, 1:1, v/v, Merck, Darmstadt, Germany) was used as an extracting
solvent. The SDE process was allowed to proceed for 2 h, and the extract thus obtained
was dried over anhydrous sodium sulphate (Merck) and filtered through Whatman No.
1 filter paper. The filtered extract was then concentrated at 40 ℃ to dryness using a
Vigreux column (i.d. 1.5 x 100 cm, Tung Kawn Glass Co., Hsinchu, Taiwan) and the
resulting essential oil was weighed and stored at -20 ℃ before use.
The essential oil obtained was redissolved in the same solvent mixture mentioned
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above and analysed using an HP 6890 gas chromatograph (GC) coupled to an HP 5973
mass selected detector (MSD, EI mode, 70 eV, HewlettePackard, Palo Alto, CA, USA).
A fused silica capillary column (DB-1, J&W Scientific, Folsom, CA, i.d. 0.25 mm , 60
m, 0.25 mm film thickness) was used and interfaced directly into the ion source of the
MSD. Heliumwas used as a carrier gas at the flow rate of 1 mL/min. The column
temperature was programmed from 40 to 220 ℃ at 3 ℃/min. Temperatures for GC
injector and GC-MSD interface were 250 ℃ and 265℃, respectively. A split ratio of 50
to 1 was used.
Volatile components were identified on the basis of gas chromatographic retention
indices, mass spectra from Wiley MS Chemstation Libraries (6th edition, G1034, Rev.
C.00.00, Hewlette Packard) and the literature (Adams, 1995; Jennings & Shibamoto,
1980). Some components were further identified using authentic compounds, which
were commercially available (Sigmae Aldrich). The relative amount of each individual
component of the essential oil was expressed as the percentage of the peak area relative
to total peak area. Kovats retention indices (Kovats, 1965) were calculated for each
separate component against n-alkanes standard (C8-C25, Alltech Associates, Deerfield,
IL, USA) according to Schomberg and Dielmann (1973), using the same DB-1 column.
3.6. Assays of antioxidant properties
For ethanolic extraction, sample powder (10 g) was extracted with 100 mL of
ethanol at 25 _C with stirring for 24 h and filtering through Whatman No. 1 filter paper.
The residue was re-extracted twice as described above. The combined ethanolic
extracts were then rotary evaporated at 40℃ to dryness. For hot water extractions,
sample powder (10 g) was heated with 200 mL deionised water at reflux for 1 h,
centrifuging at 5000 x g for 15 min and
filtering through Whatman No. 1 filter paper. The residue was reextracted twice as
described above. The combined hot water extracts were freeze dried, respectively. The
dried extract was redissolved in water or ethanol to a concentration of 50 mg/mL and
stored at 4℃ before use.
Trolox equivalent antioxidant capacity (TEAC) was determinedusing the method of
Arnao, Cano, Hernandez-ruiz, Garcia-Canovas, & Acosta, (1996) with some
modification. Aqueous or ethanolic extract (0.1-20 mg/mL), 1.5 mL of deionised water,
0.25 mL of 1000 mmol/L 2,20-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS,
SigmaeAldrich), 0.25 mL of 500 mmol/L hydrogen peroxide and 0.25 mL of
peroxidase (44 unit/mL) were mixed and left to stand for 1 h in the dark to produce
blue-green colour, and the absorbance was then measured at 734 nm against a blank.
The absorbance was quantified by the calibration curve of 6-hydroxy- 2,5,7,8-tetramethylchromane-2-carboxylic acid (Trolox, Sigmae Aldrich) as a standard and
expressed as micromole Trolox per gram.
Ferric reducing ability of plasma (FRAP) was determined using the method of
Pulido, Bravo, and Saura-Calixto (2000). Aqueous or ethanolic extract in water or
ethanol (30 mL) was mixed with FRAP
reagent (SigmaeAldrich, 900 mL) and deionised water (90 mL) and left to stand for 30
min, and the absorbance was then measured at 595 nm against a blank. The absorbance
was quantified by the calibration curve of Trolox as a standard and expressed as
micromole Trolox per gram.
Scavenging ability on 1,1-diphenyl-2-picrylhydrazyl (DPPH) radicals was
determined using the method of Shimada, Fujikawa, Yahara, and Nakamura (1992).
Aqueous or ethanolic extract (0.1e 20 mg/mL) in methanol (4 mL) was mixed by
vortex with 1 mL of methanolic solution containing DPPH radicals (SigmaeAldrich),
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resulting in a final concentration of 0.2 mmol/L DPPH and left to stand for 30 min in
the dark, and the absorbance was then measured at 517 nm against a blank. The
scavenging ability was calculated as follows: Scavenging ability (%) = [(A517 of
control - A517 of sample)/ A517 of control] x 100.
Chelating ability was determined using the method of Dinis, Maderia, and Almeida
(1994). Aqueous or ethanolic extract in water or ethanol (1 mL) was mixed with 3.7
mL of methanol and 0.1 mL of 2 mmol/L ferrous chloride. The reaction was initiated
by the addition of 0.2 mL of 5 mM ferrozine (SigmaeAldrich). After 10 min at room
temperature, the absorbance of the mixture was determined at 562 nm against a blank.
EC50 value (mg extract/mL) is the effective concentration at which DPPH radicals
were scavenged by 50%; and ferrous ions were chelated by 50% and were obtained by
interpolation from linear regression analysis. Ascorbic acid and butylated
hydroxyanisole (BHA, SigmaeAldrich) were used for scavenging ability comparison
whereas ethylenediaminetetraacetic acid (EDTA, SigmaeAldrich) was used for
chelating ability comparison.
3.7. Statistical analysis
All triplicate data were subjected to an analysis of variance for a completely
randomized design using SPSS statistical software system (version 16.0, SPSS Inc,
Chicago, IL, USA). For the mean separation, Duncan’s multiple range tests were used
to determine the
mean difference at the level of P = 0.05.
4. Results and discussion
4.1. Proximate composition
Fresh Chu-gingerwas moister than fresh Guangdong-ginger (Table 1). In other words,
GG and CG contained 15.84 and 10.86 (g/100 g) of dry matter, respectively. The
profile of proximate compositions of two ginger rhizomes in carbohydrate, fat and fibre
contents was similar. However, the content of ash in CG was higher whereas that of
protein in GG was higher. Comparing to other research it revealed ginger rhizome
constitutes of essential oil (1-2.7 g/100 g), acetone extract (3.9e9.3 g/100 g), crude
fibre (4.8- 9.8 g/100 g), and starch (40.4-59 g/100 g) (Natarajan et al., 1972).
4.2. Organic acids
Two typical tastes, including sour and pungent taste, are significant in ginger
rhizomes. The contents of organic acids and their varieties are of great importance for
their application in novel functional foods or normal cuisine. Five organic acids found
in two ginger rhizomes included citric, malic, oxalic, succinic, and tartaric acids (Table
2). Contents of citric, malic and succinic acids were relatively low in ginger rhizomes
(0.02-0.12 mg/g dry weight). Oxalic and tartaric acids were two major acids in ginger
rhizomes. However, oxalic acid was higher in CG whereas tartaric acid was higher in
GG. Total contents of organic acids were 37.33 and91.06 mg/g dry weight for GG and
CG, respectively. It seems that CG would be 2.4-fold sourer than GG.
4.3. Gingerols, shogaol and curcumin
6-gingerol and 6-shogaol are the major gingerol and shogaol present in the rhizome
(Connell & McLachlan, 1972). Gingerols and shogaols in ginger rhizomes are
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responsible for the pungent taste (Kikuzaki,Kawasaki, & Nakatani, 1994). Their
contents were in the descending order of 6-gingerol, 6-shogaol, 8-gingerol and 10gingerol for two ginger rhizomes (Table 3). Although some differences in individual
component content were found, total contents of gingerols and shogaol were similar
and were 7.52 and 7.39 mg/ 100 g dry weight for GG and CG, respectively. Shogaols,
more pungent than the gingerols, are usually derived from the corresponding gingerols
during thermal processing or long-term storage (Zhang, Iwaoka, Huang, Nakamoto, &
Wong, 1994). However, only 6-shogaol was found in fresh ginger rhizomes. Another
active component found in two ginger rhizomes was curcumin and its content in GG
was much higher than that in CG (Table 3). Curcumin possess a variety of biological
activities, such as antioxidant, antiinflammatory, antiviral, antibacterial, antifungal, and
anticancer properties, etc. (Joe, Vijaykumar, & Lokesh, 2004). Curcumin was also
found to be good antioxidant and show better antioxidative efficiency when compared
to butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), a-tocopherol
and trolox in vitro (Ak & Gulcin, 2008). Previous studies have confirmed that
curcumin and its analogues show strong hepatoprotective effects against oxidative
damage caused by ethanol (Graham, 2009). In in vitro experiments too curcumin
inhibited iron catalysed lipid peroxidation in liver homogenates, scavenged nitricoxide
spontaneously generated from nitroprusside and inhibited heat induced haemolysis of
rat erythrocytes (Naik, Thakare, & Patil, 2011). It seems that the higher curcumin
content in GG would provide more beneficial effects in health.
4.4. Volatile components
Using the SDE method, the yields of the essential oil were 0.18 ± 0.02 and 0.21 ±
0.02% dry weight for GG and CG, respectively. Generally, the essential oils from two
ginger rhizomes exhibited similar volatile profiles, except for some quantitative
differences (Table 4S, Supplementary Material). Totally, 60 different compounds
identified from the essential oil of GG quantized as percent area, included 14
monoterpenoids (11.92%), 18 sesquiterpenoids (51.54%), 6 oxygenated
sesquiterpenoids (4.57%), 5 aldehydes (17.39%), 4 ketones (0.57%), 7 alcohols
(3.45%), 2 esters (0.21%), and 4 miscellaneous compounds (0.41%). In addition, 65
different compounds identified from the essential oil of CG included 14
monoterpenoids (28.22%), 21 sesquiterpenoids (16.47%), six oxygenated
sesquiterpenoids (4.92%), 5 aldehydes (14.50%), 4 ketones (0.50%), 8 alcohols
(2.91%), 2 esters (0.18%), and 5 miscellaneous compounds (0.57%). Obviously,
monoterpenoids, sesquiterpenoids and aldehydes were three major classes of
compounds found in the essential oils.
Eight major components detected in the essential oils (>4.5%) were camphene (6.27
and 9.14%), sabinene (8.16 and 10.67%), α-curcumene (8.42 and 6.66%), zingiberene
(20.85 and 17.55%), α-farnesene (7.42 and 4.77%), β-sesquiphellandrene (8.13 and
7.32%), neral (8.00 and 6.74%), and geranial (8.70 and 7.20%), for GG and CG,
respectively. Camphene shows a terpeney-camphoraceous taste whereas sabinene
exhibits a warm, oily-peppery, woody-herbaceous and spicy taste with slightly pungent
mouthfeel (Arctander, 1969). a-Curcumene shows a characteristic odour of turmeric
and slightly pungent bitter taste (Jain, Shrivastava, Nayak, & Sumbhate, 2007).
Zingiberene is a major component of ginger oil and has a warm, woody-spicy and very
tenacious odour whereas a-farnesene shows a very mild, sweet and warm odour
(Arctander, 1969). Neral and geranial are widely used as a powerful lemon-fragrance
chemical (Arctander, 1969). Overall, ginger rhizomes would give a typical spicy ginger
odour and taste. Generally, the essential oil of plants showed some antimicrobial
activities (Williams, Stockley, Yan, & Home, 1998; Zaika, 1988). In addition, gingerols
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exhibited potent antibacterial activity (Park et al., 2008). Thus, the essential oil of
ginger rhizomes with potential antimicrobial activity might be useful for therapeutic
use.
4.5. Antioxidant properties
Yields of aqueous and ethanolic extracts from GG were 11.95 ± 0.05 and 8.96 ±
0.08 (g/100 g); and those from CG were 8.44 ± 0.16 and 6.96 ± 0.13 (g/100 g),
respectively. It seems that the yields of hot water and ethanol extracts from GG were
higher from those from CG whereas the yields of ethanolic extracts from both ginger
rhizomes were lower. The antioxidant capacity of ginger rhizomes was measured by
the TEAC method and the results were expressed as the equivalent of the standard
Trolox for comparison. The TEAC values of ethanolic extracts were 5.8-fold higher
than those of aqueous extracts for both ginger rhizomes (Table 4). However, the TEAC
values from GG and CG were comparable for aqueous (0.17-0.18 mmol/g) and
ethanolic extracts (098-1.04 mmol/g).
The reducing power of ginger rhizomes was measured by the FRAP method and the
results were also expressed as the equivalent of the standard Trolox for comparison.
The FRAP values of ethanolic extracts were 7.2-8.0-fold higher than those of aqueous
extracts for both ginger rhizomes (Table 4). However, the FRAP values of ethanolic
extracts from CG and GG were comparable whereas the FRAP values of the aqueous
extract from GG was higher than that from CG (P < 0.05). With regard to the TEAC
and FRAP methods, both ethanolic extracts were more effective than both aqueous
extracts.
The scavenging ability assayed is the ability of extracts to react rapidly with DPPH
radicals and reduce most DPPH radical molecules. All EC50 values were in the range
of 2.81-5.57 mg/mL, indicating that both extracts from two ginger rhizomes were
relatively effective in scavenging abilities on DPPH radicals (Table 4). Aqueous
extracts were more effective than ethanolic extracts for both ginger rhizomes as
evidence by their lower EC50 values. In
addition, EC50 values of CG were lower than those of GG for both extracts. However,
ascorbic acid and BHA were much more effective with their EC50 values being 0.65
and 0.14 mg/mL, respectively.
Ferrous ions play an important role as catalysts in oxidative process, leading to the
formation of hydroxyl radicals and hydroperoxide decomposition by Fenton reaction.
The chelating ability assayed is the ability of extracts to inhibit the complex formation
of ferrozine with ferrous ions. Aqueous extracts were 16.8e22.9-fold more effective in
chelating abilities on ferrous ions than ethanolic extracts for both ginger rhizomes as
evidence by their lower EC50 values (Table 4). In addition, EC50 values of CG were
lower than those of GG for both extracts. However, EDTA was much more effective
with its EC50 value being 0.14 mg/mL.
With regard to four antioxidant properties assayed, two extracts from two ginger
rhizomes were relatively effective. However, both extracts from CG were slightly more
effective than those from GG. Overall, ethanolic extracts were more effective in TEAC
and FRAP values whereas aqueous extracts were better at scavenging and chelating
abilities. Fresh ginger methanolic extract exhibits hypotensive, endotheliumindependent vasodilator and cardio-suppressant properties (Ghayur, Gilani, Afridi, &
Houghton, 2005). Meanwhile, the fresh ginger aqueous extract showed it lowers blood
pressure (BP) effect through cholinergic and calcium channel blocking (CCB)
properties in experimental animals (Ghayur et al., 2005).
These results might suggest higher medical suitability of alcoholic and extracts
ethanolic in various antioxidant applications.
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5. Conclusion
In this research, two ginger rhizomes were comparable in carbohydrate, fat and fibre
contents. Oxalic and tartaric acids were two major acids in ginger rhizomes. However,
total content of organic acids was much higher in CG than in GG. Total contents of
gingerols and shogaol in two ginger rhizomes were similar but the content of curcumin
was higher in GG. Generally, the essential oils from two ginger rhizomes exhibited
similar volatile profiles andmonoterpenoids, sesquiterpenoids and aldehydes were three
major classes of compounds found. Totally, 60 and 65 different compounds were
identified from the essential oil of GG and CG, respectively. Eight major components
detected in the essential oils (>4.5%), which would give a typical spicy ginger odour
and taste, were camphene, sabinene, a-curcumene, zingiberene, a-farnesene, bsesquiphellandrene, neral, and geranial.
With regard to the antioxidant properties in terms of TEAC and FRAP methods, both
ethanolic extracts from ginger rhizomes were more effective than both aqueous extracts.
On the contrary, aqueous extracts were more effective than ethanolic extracts in
scavenging and chelating abilities. With regard to four antioxidant properties assayed,
both extracts from CG were slightly more effective than those from GG. Based on the
results obtained, two ginger rhizomes could be used as a flavouring agent in food and
also in the medicinal applications as an antioxidant.
Appendix A. Supplementary data
Supplementary data related to this article can be found at
http://dx.doi.org/10.1016/j.lwt.2013.08.003.
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