The medicinal value of plants has attained a more important dimension in the
past decade due to the fact that their extracts have been found to contain not
only minerals but also a diverse array of secondary metabolites or phytochemicals
with antioxidant potentials (Akinmoladun et al.,
2007; Ahenkora et al., 1998). Studies have
indicated that these phytochemicals especially polyphenols have high free radical
scavenging activity which helps to reduce the risk of chronic diseases such
as cardiovascular diseases, cancer, diabetes mellitus, etc. (Ames
et al., 1993).
Free radicals which have been implicated in these diseases are generated in the human body through numerous sources including normal body metabolism, exposure to toxins, etc and they exist in different forms including superoxide, hydroxyl, hydroperoxyl, peroxyl and alkoxyl radicals.
Ginger (Zingiber officinale), a widely used herb and food flavoring
agent is considered a major constituent of the diet (Sertie
et al., 1991). Its medicinal properties against digestive disorders,
rheumatism and diabetes have been reported (Afzal et al.,
2001). The medicinal value of ginger has been linked to its antioxidant
characteristics since it can scavenge superoxide anion and hydroxyl radicals
(Kar et al., 1999). In addition, its neutraceutical
properties have long been of interest to the food processing and pharmaceutical
industries. The volatile essential oils that contribute to the characteristic
flavor of ginger varies from 1.0-3.0% while the oleoresin that is responsible
for its pungent flavor ranges from 4.0-7.5% and also possesses substantial antioxidant
activity (Balachandran et al., 2006).
As the medicinal value of ginger has been linked to its antioxidant potentials
arising from the amounts of oleoresin and polyphenols present in it and being
that these are new ginger varieties, it would be worthwhile to investigate the
amounts of oleoresin and polyphenols present in it. In addition, the knowledge
of the chemical composition of a plant together with it antioxidant activity
can give a fair estimate of its therapeutic potential (Akinmoladun
et al., 2007).
This thus led to the study which was designed to investigate the physico-chemical properties and antioxidant potentials of six new varieties of ginger.
MATERIALS AND METHODS
Quercetin(3,3,4,5,7-pentahydroxyflavone), 1,1-Diphenyl-2-picrylhydrazyl (DPPH), sodium dihydrogen orthophosphate (NaH2PO4), Disodium hydrogen orthophosphate (Na2HPO4), Phenol and Ferric chloride used were products of Sigma Chemical Company (UK). All other chemicals used were purchased from Associated Laboratories, Aba, Abia State, Nigeria and were of analytical grade.
Six varieties of ginger UGII 7GY5, UGI 5GY3, UGII 11GY11, UGII 7GY25, UGII 5GY6 and UGII 9GY3, freshly harvested from the experimental farm of National Root Crops Research Institute, Umudike, Nigeria in 2011 were used for the plant experiments. They were thoroughly washed, peeled, dried in an oven at a temperature of 50°C before being ground into flour using a food processor and analyzed.
Extraction of the sample: One gram of sample was weighed accurately and suspended in 100 mL of solvent. It was shaken for 3 h in an electronic shaker at room temperature, centrifuged at 4000 rpm for 20 min and filtered with Whatman No. 1 filter paper. For all experiments, fresh extracts were used.
Physicochemical properties of ginger: The AOAC (1980)
methods was used in the determination of the phenolic, oleoresin, fat, dry matter,
crude fibre and ash contents of the six ginger varieties.
Free radical scavenging activity determination: The stable 2,2 diphenyl-1-picryldydrazyl (DPPH) radical was used for the determination of free radical scavenging activities of the extracts. A portion (1 mL) each of the different concentrations (1000, 500, 250, 125, 62.5, 31.25 ug mL-1) of the extracts or standard (Quercetin) in test tubes was added to 1 mL of 0.3 mM DPPH in methanol. The mixtures were vortexed and then incubated in a dark chamber for 30 min after which the absorbances were measured at 517 nm against a DPPH control containing only 1 mL of methanol in place of the extract. The percentage scavenging activity was calculated using the expression:
IC50 values denote the concentration of the sample which is required
to scavenge 50% DPPH free radicals. Higher IC50 values denote lower
Reducing power tests: The reducing property of the unripe plantain flour
was determined by assessing the ability of the sample extracts to reduce FeCl3
solution as described by Oluwaseun and Ganiyn (2008)
and modified by Chinedum et al. (2011). The extracts
of the ginger varieties were prepared for the assay by dissolving 2 g of the
flours in 40 mL of methanol and filtering with Whatman No. 1 filter paper. The
resulting solutions were made up to 50 mL with methanol. The absorbance was
taken at 700 nm against a reagent blank using a spectrophotometer. Increased
absorbance reading indicates increased reducing power.
RESULTS AND DISCUSSION
In recent years, phenolics have attracted the interest of researchers because
they show promise of being powerful antioxidants that can protect the human
body from free radicals, the formation of which is associated with the normal
metabolism of aerobic cells (Oboh and Rocha, 2007). That
the phenolic compounds present in plants possess antioxidant activity and may
help protect cells against the oxidative damage caused by free radicals has
been reported (Kirakosyan et al., 2003).
The high phenolic contents of the six varieties of ginger investigated is the significant finding of this study as it suggests that they may contain high quantities of antioxidants. The phenolic content of UGII7GY25, though not significantly different from that of UGII5GY6 was observed to be the highest (5.69±0.06) among other varieties studied while UGII 7GY5 had the least (4.69±0.16).
Oleoresin is responsible for the pungent flavor of ginger and it also possesses
substantial antioxidant activity in addition.Values obtained for the oleoresin
contents were below that obtained by Balachandran et
al. (2006) who reported the oleoresin contents of ginger to range from
4.0 to 7.5%. This explains the mild pungent odor of these ginger varieties.
Fat makes up about 99% of the real fraction of a food. Usually in food analysis,
total lipid content is what determined rather than the true fat content. Vadivel
and Pugalenthi (2006) reported the percentage lipid contents of ginger to
be about 0.9%. The lipid content of UGII7GY25 (0.7±0.00) was significantly
higher than other varieties studied while that of UGII 11GY11 was the least
(0.25±0.00). Values obtained were slightly higher than the recommended
daily allowance for an adult man (Deb, 1999). The low
total lipid contents of the ginger varieties as obtained in Table
1 suggests that they can be used in the management of patients with high
blood pressure and heart diseases.
Dry matter relates to good cooking qualities. Higher dry matter contents suggests
better cooking qualities and extended storage lives. UGII5GY6 had the highest
dry matter content (49.85±5.05) while UGII7GY5 had the least (22.7±3.67).
Crude fibre represents that portion of food not used up by the body but mainly
made up of cellulose together with a little lignin and is known to increase
bulk stool (Selke, 1990). In addition, crude fibre aids
digestion, absorbs water and makes stool larger and softer, so preventing constipation
(Ayoola and Adeyeye, 2009). Dietary fibre has recently
gained much importance as it is said to reduce the incidence of colon cancer,
diabetes, heart disease and certain digestive diseases.
|| Physico-chemical properties of six new varieties of ginger
|Each value in the table is the average of triple experiments±standard
deviations. Values with the same superscripts down each row are not significantly
different from each other
The crude fibre content of UGII 11GY11 though not statistically different from
that of UGII5GY6, UGII9GY3 and UGI5GY3 was the highest among other ginger varieties
studied (1.9±0.13) while UGII 7GY25 had the least (1.2±0.04).
Values obtained were lower than 2.4% being the reported values as the fibre
content of ginger.
Ash is a reflection of the quantity of minerals in a sample. Generally, the
ash content of foods is often small (less than 1% of the food). The values obtained
for UGI5GY3 (2.6±0.44) (which was significantly higher than all the varieties
studied) and UGII 11GY11 (1.5±0.03) (though not significantly different
from UGII7GY5) were higher than that obtained by Vadivel
and Pugalenthi (2006) (Table 1). However values obtained
for UGII7GY25, UGII5GY6 and UGII9GY3 were below the reported values for ginger
while values obtained for UGII7GY5 were in agreement with earlier works by Vadivel
and Pugalenthi (2006) who reported the ash contents of ginger to be around
DPPH radical scavenging activity: The effect of antioxidants on DPPH
is thought to be due to their hydrogen donating ability. The DPPH radical is
a free radical stable at room temperature. The antioxidant activities of the
extracts and Quercetin were in the order :Quercetin>UGII7GY25>UGII5GY6>UGII9GY3>UGI5GY3>UGII
11GY11>UGII 11GY11. The inhibitory activities of the extracts on DPPH free
radical indicates that the extracts have a proton-donating ability and could
serve as free radical inhibitors or scavengers, acting possibly as primary antioxidants.
The inhibitory actions of the varieties of ginger is attributed to the phenolic
content and presence of other phytochemicals in them. Kirakosyan
et al. (2003) have reported that polyphenols present in plants are
responsible for their antioxidant activities leaving us to suggest that the
antioxidant activities of these ginger varieties could have come from their
phenolic contents. The over production of reactive oxygen species following
the ingestion of certain chemicals or drugs (xenobiotics) or when the levels
of antioxidants are diminished (such as inactivation of enzymes involved in
the disposal of oxygen species) causes a shift from the antioxidants to the
pro-oxidants leading to oxidative stress which can lead to tissue damages and
necrosis in many instances. Antioxidants function in maintaining a balance between
these pro-oxidants and the antioxidant status thus protecting the body from
tissue damage arising from these pro-oxidants. Results indicate that these ginger
varieties might be useful therapeutic agents for treating radical- related pathological
damage (Table 2).
Reducing power is a measure of the ability of the extracts to reduce Fe3+
to Fe2+. Substances which have reduction potential react with potassium
ferri-cyanide (Fe3+) to form potassium ferro-cyanide (Fe2+)
which then reacts with ferric chloride to form ferric ferrous complex that has
an absorption maximum at 700 nm. Reducing power has become one of the antioxidant
capability indicators of medicinal plants (Duh and Yen,
1997) as it may accord with overall antioxidant activity.
|| DPPH radical scavenging activity of six Ginger varieties
|Linear equation: (a) y = 27.60x+9.985 (b) y = 27.09x+9.077
(c) y = 28.92x+3.718 (d) y = 30.97x-3.835 (e) y = 34.27x-17.08 (f) y = 33.93x-
21.78 (g) y = 34.28x+3.209
This is because antioxidants are strong reducing agents and this is principally
because of the redox properties of their hydroxyl groups and the structural
relationships of any parts of their chemical structure (Oboh
and Rocha, 2007; Chinedum et al., 2011).
Benzie and Strain (1996) also considered antioxidants
as any specie that reduces the oxidizing species that would otherwise damage
|| Reducing power of Ugll 7GY25 and Ugll 5GY6
|| Reducing power og Ugll 9GY3 and Ugll 7GY5
|| Reducing power of Ugl 5GY3 and Ugll 11GY11
Results obtained in Fig. 1-4 suggest that
all the flours except UGII 9GY3 have a strong antioxidant activity.
|| Correlation between percentage oleoresin and phenol content
of 6 ginger varieties
Correlation of the total phenolic content versus the total oleoresin content was negative suggesting that the oleoresin contents of the ginger varieties could not have come from the phenols present in the ginger.
The physico-chemical properties and antioxidant potentials UGII 7GY25, UGII5GY6, UGII9GY3, UGII7GY5, UGI5GY3 and UGII 11GY11 have been demonstrated in this study.
The total phenolic contents of the varieties of ginger studied were found to be quite high, suggesting their high antioxidant potentials. In addition, the oleoresin contents of the ginger varieties which were low could not have come from their total phenolic contents, explaining the mild pungent odor of the ginger varieties. The low total lipid contents of the ginger varieties suggest that they can be used in the management of patients with high blood pressure and heart diseases. In addition, the mineral contents of UGI5GY3 and UGII 11GY11 were higher than the reported mineral contents of ginger.
Finally, with the exception of UGII 9GY3, all other varieties of ginger studied
were found to possess strong antioxidant activities.
The authors wish to thank the Biochemistry department of National Root Crops Research Institute, Umudike, Umuahia, Abia State, Nigeria for the assistance they rendered during this research work.