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International Journal of Food Properties
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Screening for Antioxidant Activity,
Phenolic Content, and Flavonoids from
Australian Native Food Plants
Sarana Sommano
a
b
, Nola Caffin
b
& Graham Kerven
b
a
Science and Technology Research Institute, Chiang Mai University ,
Chiang Mai , Thailand
b
School of Agriculture and Food Sciences , The University of
Queensland , Brisbane , Australia
Accepted author version posted online: 19 Oct 2012.Published
online: 09 May 2013.
To cite this article: Sarana Sommano , Nola Caffin & Graham Kerven (2013): Screening for Antioxidant
Activity, Phenolic Content, and Flavonoids from Australian Native Food Plants, International Journal of
Food Properties, 16:6, 1394-1406
To link to this article: http://dx.doi.org/10.1080/10942912.2011.580485
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International Journal of Food Properties, 16:1394–1406, 2013
Copyright © Taylor & Francis Group, LLC
ISSN: 1094-2912 print / 1532-2386 online
DOI: 10.1080/10942912.2011.580485
SCREENING FOR ANTIOXIDANT ACTIVITY, PHENOLIC
CONTENT, AND FLAVONOIDS FROM AUSTRALIAN
NATIVE FOOD PLANTS
Sarana Sommano
1,2
, Nola Caffin
2
, and Graham Kerven
2
1
Science and Technology Research Institute, Chiang Mai University, Chiang Mai,
Thailand
2
School of Agriculture and Food Sciences, The University of Queensland, Brisbane,
Australia
Seven kinds of bush plants, namely, bush tomato (BT), lemon myrtle (LM), wild lime (WL),
finger lime (FL), wattle seed (WS), Davidson’s plum (DP), and Kakadu plum (KP) were
investigated for antioxidant capacity by 2,2-diphenyl-1-picrylhydrazyl radical, Trolox equiv-
alent antioxidant capacity assay, or 2,2’-azinobis-93-ethyl-benzothiazoline-6-sulfonic acid
radical, total polyphenols, and flavonoids. It was found that there was a positive correlation
between antioxidant activities examined by the two methods. However, there was a nega-
tive correlation between total phenol and each of the antioxidant activity tests; for example,
Davidson’s plum contained the phenolic content as high as 890 mg GAE/100 g while low
antioxidant activities were detected (23 TE /100 g and 45% for TEAC and % DPPH, respec-
tively). For the qualitative flavonoids test, bush tomato contained feulic acid, caffeic acid,
naringenin, and hesperetin. Lemon myrtle contained catechin, epicatechin, vanilic acid,
myricetin, kampferol, and naringenin. Finger lime contained caffeic acid and vanilic acid.
Wild lime contained epicatechin, vanilic acid, luteolin, and naringenin. Kakadupum con-
tain catechin and naringenin. Davidson’s plum contained naringenin and hesperetin. Wattle
seed contained naringenin. However, some other compounds could not be identified because
there was no standard to confirm the retention time available. Absorbance was changed for
the detection of anthocyanins in Davidson’s plums from 220–400 to 525 nm. It was shown
by liquid chromatography mass spectrometry that six major anthocyanidins (delphinidin,
cyanidin, petunidin, pelargonidin, peonidin, and malvidin) attached with the sugar molecules
(hexose and pentose) were found and the major anthocyanin was cyaniding-hexose-pentose.
This study suggests that regarding the antioxidant capacity, these Australian Native plants
have potential as functional food ingredients.
Keywords: Bioactive ingredient, Bush plants, Functional food, Liquid chromatography
mass spectrometry (LCMS).
INTRODUCTION
Recently, t heret has been an overwhelming number of researches on food science and
nutrition with regard to functional food. The term “functional food” refers to an antioxidant-
rich diet, which has a potential in lowering the risk of cardiovascular disease, diabetes,
Received 30 October 2010; accepted 8 April 2011.
Address correspondence to Sarana Sommano, Science and Technology Research Institute, Chiang Mai
University, Chiang Mai 50200, Thailand. E-mail: sarana.s@cmu.ac.th
1394
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AUSTRALIAN NATIVE FOOD PLANTS 1395
arthritis, and cancer.
[1]
There has also been a considerable interest in plants with a high
antioxidant capacity diet. Australian native plants are considered to be potential sources
of antioxidants.
[2–4]
The examples are ascorbic acid in Kakadu plum
[5]
and flavonoids in
Davidson’s plum.
[6,7]
In addition, lemon myrtle was found to deliver antibacterial and
antifungal activity.
[8]
Thus, the native food ingredients may be utilized as captivating
antioxidants for the preservation of foods and have application for human health.
[2]
Since polyunsaturated fatty acids are oxidized by either enzymatic or autox-
idation in free radical chain reactions, antioxidants can react against these two
reactions. Two types of antioxidants are categorized upon the ability to pro-
hibit the oxidation process in different stages. Primary antioxidants react against
the oxidation reaction by breaking chain reaction and/or scavenging free radicals.
Secondary antioxidants work by deactivation of metal, inhibition of the breakdown
of lipid hydroperoxides, regeneration of primary antioxidants, and singlet oxygen
quenching.
[9]
Antioxidant activity can be determined by measuring relatively stable. For the
2,2-diphenyl-1-picrylhydrazyl (DPPH) radical method, the remaining DPPH·,afterthe
reaction between DPPH· solution and donating antioxidant (AH), is measured at
517 nm at a certain time.
[10,11]
This method could be considered very rapid, and
no expensive reagents or sophisticated instruments are required.
[10,12]
Trolox equiv-
alent antioxidant capacity (TEAC) is one of the spectrophotometric methods that
have been used to determine the total antioxidant activity of solutions of pure sub-
stances, aqueous mixtures, and beverages.
[13]
TEAC assay measures the ability of an
antioxidant to quench a radical cation, which is generated by 2,2’-azinobis-93-ethyl-
benzothiazoline-6-sulfonic acid (ABTS). Various types of TEAC assay have also been
described.
[14]
Recent work on antioxidant activity on Australian native plants focused on those
methods used to evaluate lipid oxidation by the spectrophotometric method. Forbes-Smith
and Paton
[2]
examined the antioxidant activity of native plants by using the β-carotene
bleaching agar diffusion test and linoleic acid r eaction test. Netzel et al.
[7]
tested some
Australian native fruits for their antioxidant activity (DPPH), ascorbic acid, total phenolic
content, and anthocyanins. However, more work on bioactive compounds including
antioxidant level is required to promote the Australian native food industry on nutri-
tional benefits of native fruits and seeds. This study was conducted to evaluate antioxidant
capacity, total phenolic content, and flavonoids of seven Australian native food plants.
MATERIALS AND METHODS
Chemicals
General chemicals were supplied by the School of Agriculture and Food Sciences,
the University of Queensland: ABTS, 2,2
-Azino-bis(3-ethylbenzothiazoline-6-sulfonic
acid) diammonium salt; Trolox, 6-hydroxxy-2,5,7,8-tetramethylchromane-2-carboxylic
acid; DPPH, 2-Di(4-tert-octylphenyl)-1-picrylhydrazyl; and Folin–Ciocalteu reagent were
purchased from Sigma-Aldrich (NSW, Australia). The standard reagents: Kaemperol,
Luteolin, Naringenin, Myricetin, and Hesperetin were also from Sigma-Aldrich (Sydney,
Australia). The standard reagents: (−)-epicatachin, caffeic acid, ferulic acid, cinnamic acid,
vanilic acid, (+) catechin, quercetin, and anthocyanidin standards (cyaniding, delphinidin,
pelargonidin) were supplied by Analytical Services (University of Queensland).
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1396 SOMMANO, CAFFIN, AND KERVEN
Sample Preparation
Samples were collected from different producers who produce native food plants.
One kilogram of whole as well as a kilo gram of ground bush tomato in an air tight plastic
bag were collected at the production site of the producer (Rod Honna, Alice Springs, NT,
Australia). Kakadu plums were brought frozen from the producer site (Ray Hall, Winnellie,
NT, Australia). Frozen wild lime was collected from a distributor (Robins Foods, Braeside,
VIC, Australia). The whole fruits were packed into a plastic bag, which was stored in a box
topped with dried ice. Frozen Davidson’s plum, finger lime, and fine-ground dried lemon
myrtle (1 kg each) were sent from the producer (Sibylla Hess-Buschrann, Lismore, NSW,
Australia).
All samples, except dried bush tomato and lemon myrtle, were cut into thin pieces.
Stones were removed for Kakadu plum and Davidson’s plum. Sample slides were placed
onto the trays and kept frozen prior to freeze drying. The freeze dryer (Alpha 1-4 LSC,
Martin Christ, Gefriertrocknungsanlagen GmbH, Germany) was warmed up for 15–20 min
before use. Samples were put into the chamber and the machine was run overnight (at 20
◦
C
and 1 mbar). Moisture content was calculated after samples were taken out of the freeze
dryer and vacuumed in an oven until the weight was constant. Samples were kept in the
freezer for further analysis.
Solvent Extraction of Australian Native Plants
Dried sample (∼1.0 g) was added into a 50-mL polypropylene centrifuge tube and
mixed with 15 mL of hexane. It was then mixed on a rotating device for 35 min and cen-
trifuged at 25,000 rpm for 5 min. The extraction was done twice and the supernatant was
combined. The combined solvent was evaporated off under a nitrogen stream on a hot plate.
The residue sample was then dried under a vacuum oven to remove the tract solvent.
The extracting solvent was prepared by mixing methanol, acetone, and water
(7/7/6) with the addition of 0.05% ascorbic acid. Solvent (20 mL) was then added into
the dried residue and the mixture was mixed on a rotator for 35 min. The mixture was
centrifuged at 25,000 rpm for a further 10 min. The extraction was done twice and the
supernatant was combined. The combined supernatant was concentrated in the rotary evap-
orator to remove the organic component. The concentrated extracts were frozen before
drying in the freeze dryer. The extracts were store below 5
◦
C for further analysis. The
addition of 0.05% of ascorbic acid to eliminate dissolved oxygen in the extracting solvent
was only used for the flavonoid’s extraction. For the test of phenolic content, antioxidant
capacity by DPPH radical, and TEAC, the extracting solvent was used alone.
Antioxidant Activity Determination by DPPH Radical Method
Dry extract was dissolved in methanol. Samples with concentration series of 50, 100,
500, and 1000 μg/mL as well as BHT (positive control) with concentrations of 50, 100,
500, and 1000 μg/mL were prepared on the day of analysis. DPPH (1 mM) solution was
also freshly prepared. A sample of (4.0 mL) each concentration was added to a 20-mL
test tube and 1 ml of DPPH solution was added on top of the samples. The samples with
DPPH were mixed on a vortex mixer for 1 min and incubated in the dark for 35 min at room
temperature. After incubation, the absorbance at 517 nm (Ultrospec III UV/Vis, Pharmacia,
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AUSTRALIAN NATIVE FOOD PLANTS 1397
The Netherlands) was measured.
[15]
Methanol (4.0) was used as a negative control. % RSA
was calculated from the following equation:
%RSA =
absorbance control absorbance sample
absorbance control
× 100.
Antioxidant Activity Determination by TEAC Assay
Similarly to DPPH assay, the same sample concentration series was prepared. ABTS
radical solution (ABTS
◦+
) was prepared by mixing ABTS (7 mmol/L) with 2.45 mmol/L
of potassium persulfate (K
2
S
2
O
8
),
[13]
which obtained a molar ratio of 1:0.035. The solution
was left stand at room temperature to allow complete reaction and a stable absorbance for
12–24 h. To prepare the working solution, the mixture was then diluted with ethanol to
obtain the absorbance at 0.700 ± 0.020 at 734 nm and the dilution was recorded.
An adequate dilution (10 μL) of the sample was added to 1 mL of diluted ABTS
◦+
solution and the absorbance reading was taken immediately within 1 min after ini-
tial mixing for 1–15 min at 734 nm. A dose-response curve was derived for Trolox
(0, 25,100,400 mg/L). The percentage of exhibition of both standards and the samples
were calculated when the absorbance readings were constant (after 10 min). Values were
expressed as Trolox equivalent (TE) per gram of the sample.
Phenolic Content by Folin-Ciocalteu Method
Appropriately diluted extracts (1.0 mL) that were diluted with methanol or standard
solutions of gallic acid (20, 40, 60, 80, and 100 mg/L) were added to a 25-mL volumetric
flask containing 9 mL of deionized H
2
O (DI).One milliliter of 10% Folin-Ciocalteu reagent
was added to the mixture and shaken for 5 min. Then, 10 mL of 7% Na
2
CO
3
was added
to the mixture. The solution was finally brought to volume with DIH
2
O using a 25-mL
volumetric flask. The incubation was taken for 90 min at room temperature. The absorbance
was read at 750 nm using DIH
2
O as a blank.
[16]
Total phenolic contents were expressed as
mg gallic acid equivalents (GAE)/100 g sample.
Qualitative Screening of Flavonoids in Bush Plants
Mixed standard 1 was prepared by dissolving (−)-epicatachin, caffeic acid, ferulic
acid, cinnamic acid, vanillic acid, and (+) catechin. Each of them was prepared at a concen-
tration of 50 μg/mL in 20% acetronitrile (ACN). The concentration of 25 μg/mL of mixed
myricetin, quercetin, luteolin, and kampferol in 20% ACN were prepared and named as
mixed standard 2. Fifty μg/mL of hesperetin and naringeninin 20% ACN were also mixed
(mixed standard 3). Dried extract was redissolved with 2 mL of 20% ACN. The samples
were then dissolved in solution by a sonicator filled with warm water. The liquid samples
were filtrated through a 0.45-μm nylon filter and then injected into liquid chromatography
mass spectrometry (LCMS) (Alliance 2690 HPLC, Waters, USA) using the Electrospray
Ionisation in positive mode (ESI+). The compounds were distinguished using a mass scan
detector and were confirmed with the retention time of the standards. The separation of
the compounds was readily achieved on an X-terra column (150 × 2.1 mm, φ 3.5 μm)
with the gradient mobile phase (A: 2% ACN 0.1% formic acid; B: 80% ACN 0.1% formic
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1398 SOMMANO, CAFFIN, AND KERVEN
acid). Total running time was 35 min with a flow rate of 0.25 mL/min. The flavonoid com-
pounds were detected individually with wavelengths ranging from 220–400 nm. However,
as Davidson’s plum contains a high amount of anthocyanins and the anthocyanins are
detected at 525 nm, the standards and the methods of detection were slightly changed.
For the analysis of anthocyanin (anthocyanidins conjugated with sugars) in
Davidson’s plum, the conditions for ionization of the reference anthocyanidins (cyanidin,
delphinidin, and pelargonidin) was optimized for ESI+ mode taking advantage of the +
ionizable site present in the flavium ring structure. A cone voltage was adjusted from 25,
50, to 80 V and a better condition was chosen. In the absence of reference anthocyanidins
for other compounds, the standards of cyaniding and delphinidin were used to qualify the
peak area for all anthocyanin present.
Statistical Correlation Between the Tests for Antioxidant Activity and
Total Phenols
Statistical correlation between each of the antioxidant activity tests (DPPH radical
and TEAC) and total phenols was analyzed by Pearson analysis using Minitab
®
statistic
software, version 14 (Minitab, USA).
RESULTS AND DISCUSSION
Radical scavenging activity (%RSA) by DPPH method of some of the bush plants
is shown in Fig. 1. At the higher concentration (i.e., 1000 μg/mL), all bush plant sam-
ples gave relatively high activity (∼50–90%). The highest radical scavenging activity
was Kakadu plum followed by lemon myrtle, finger lime, bush tomato, wild lime, wat-
tle seed, and Davidson’s plum, which possibly is due to its high ascorbic acid content
(406–5320 mg/100 edible potion).
[17,18]
Moreover, DPPH assay reacts rapidly to ascorbic
acid since the condition of the assay does not have an adverse effect to ascorbic acid and
iso ascorbic acid.
[12]
Unpublished data also agree with this (Dyah, personal communica-
tion). However, Davidson’s plum showed the lowest activity. This might be due to the fact
that Davidson’s plum also contains a purple pigment that interferes with the initial color of
DPPH solution (purple).
[12]
This antioxidant study was then confirmed by TEAC assay. The
effect of time on the suppression of the absorbance of the radical was also studied. It was
observed that the absorbance of the samples appeared to be constant after 10 min (data not
shown). Consequently, the percentage of the exhibition of the samples was calculated at
10 min and expressed as Trolox equivalent. It was discovered (Table 1) that wattle seed
gave the highest antioxidant capacity followed by Kakadu plum, lemon myrtle, wild lime,
bush tomato, finger lime, and Davidson’s plum, respectively. In relation to % RSA con-
veyed by DPPH radical method, Kakadu plum still showed the highest antioxidant activity.
In contrast, the highest amount of phenols was Davidson’s plum followed by bush tomato,
finger lime, wild lime, Kakadu plum, lemon myrtle, and wattle seed, respectively. Positive
correlation between antioxidant expressed by DPPH and ABTS radical method was found
(P = 0.14). The total phenolic content is generally responsible for antioxidants and is well
correlated with other antioxidant assays.
[19,20]
However, in our study, a converse correlation
was found when comparing the amount of total phenol with the antioxidant capacity and
these two methods (P < 0.05) (Table 2).
Further analysis on other bioactive compounds and flavonoids was evaluated using
LCMS. The common standards were prepared, which were comprised of (-)-epicatachin,
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AUSTRALIAN NATIVE FOOD PLANTS 1399
0 20 40 60 80 100
BT
WL
FL
WTS
DP
LM
KKP
% radical scavenging activity (DPPH)
250 µg/mL 500 µg/mL
1000 µg/mL
Figure 1 Radical scavenging activity of bush plants at the different concentrations (unit: μg/mL). The values are
mean of the duplication.
Tab le 1 Percent radical scavenger activity (DPPH), antioxidant capacity, and total
phenol in bush plants.
Sample
% radical scavenger activity
by DDPH at 1000 μg/ml
TEAC
TE/100 g
Total Phenols
mg/100 g
BT 84.26 45.92 702.9
WL 80.74 53.09 451.6
FL 87.20 28.46 457.5
DP 48.82 23.39 893.1
KKP 91.47 61.24 307.6
WTS 81.17 64.21 265.6
LM 88.24 54.22 265.6
Values are mean of duplication.
Tab le 2 Pearson’s correlations between antioxidant potential by DPPH radical,
TEAC, and total phenols.
% RSA (DPPH) TEAC
TEAC 0.621
0.137
Phenol −0.780 −0.771
0.039 0.042
Cell Contents: Pearson correlation
P-Value
caffeic acid, ferulic acid, cinnamic acid, vanilic acid, (+) catechin, myricetin, quercetin,
luteolin, kampferol, hespertin, and naringinin. Table 3 illustrates the compounds found in
some bush plants. Flavonone (hesperetin, naringenin) was found in bush tomato. Some
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1400 SOMMANO, CAFFIN, AND KERVEN
Tab le 3 Molecular weight and retention time of some compounds found in some bush plants.
Mw
Bush plants Standards Mw-1 RT (min) detected RT (min)
Bush tomato Ferulic acid 193 18.21 193 18.23
Caffeic acid 179 12.95 179 12.99
Naringenin 271 23.79 273 24.17
Hesperetin 301 24.12 301 24.46
Lemon
myrtle Catechin 289 11.39 289 11.34
Epicatechin 289 14.89 289 14.88
Vanilic acid 167 12.35 167 12.35
Myricetin 317 21.11 317 21.07
Kampferol 285 22.76 285 22.76
Naringenin 271 23.75 271 23.8
Finger lime Caffeic acid 179 13.4 179 13.43
Vanilic acid 167 12.35 167 12.35
Wild
(round)
lime Epicatechin 289 15.32 289 15.24
Vanilic acid 167 12.35 167 12.31
Luteolin 285 24.14 285 24.21
Naringenin 271 23.79 271 23.75
Kakadu
plum Catechin 289 11.39 289 11.36
Naringenin 271 23.75 271 23.75
Davidson
plum Naringenin 271 23.79 271 23.75
Hesperetin 301 24.12 303 24.05
Wattle seed Naringenin 271 23.79 271 23.79
Standards were freshly prepared for each of the samples.
of the compounds from flava-3-ols, flavonols, and flavononeds were seen in lemon myr-
tle. Some compounds in flavan-3-ols, flavones, flavonones group were found in wild
lime, wattle seed, and Davidson’s plum was found compounds from flavonones. Kakadu
plum contained (+) catechin and naringinin, which were a member of flavan-3-ols and
flavonones, respectively. Finger lime contained caffeic and vanillic acid. However, there
were some other peaks in the samples that cannot be identified and some expected com-
pounds, such as epicatechingallate and epigallocatechingallate in Davidson’s plum
[6]
have
yet been evaluated due to the limitation of the standards.
The conditions for ionization of the reference anthocyanidins (cyanidin, delphinidin,
pelargonidin) was optimized for ESI+ mode taking advantage of the + ionizable site
present in the flavium ring structure. For the anthocyanidins tested, a Cone voltage of
50 V was found to be essential for efficient ionization. Increasing the Cone voltage to 80 V
resulted in considerable fragmentation with useful fragments for constructing a MS Library
(Fig. 2). However, an initial test with a native fruit sample where the compounds are present
as anthocyanins showed that a Cone voltage of 50 V was too high and a Cone voltage of
25 V gave the anthocyanin M
+
molecular ion plus f ragment ions for the sequential loss of
sugar molecules and finally the anthocyanidin M
+
ion (Fig. 3).
The separation of the test anthocyanidin reference compounds was readily achieved
on an X-Terra column (150 × 2.1 mm, φ 3.5 μm) with a gradient starting at 95% A and
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AUSTRALIAN NATIVE FOOD PLANTS 1401
Figure 2 Mass scans of anthocyanidins. All ESI+ capillary voltage was 3.50 kV.
0.1% formic acid (Fig. 4). However, when the native fruit sample was r un, the correspond-
ing anthocyanins eluted earlier and were not fully resolved (Fig. 5). Further development
of the gradient program or choice of a different column may achieve separation.
For quantification purposes the absorbance at 525 nm, which is associated with the
aglycone component (anthocyanidin) of the molecule, was initially investigated using the
three reference anthocyanidins. The use of the absorbance of the aglycone component to
quantify the corresponding anthocyanins is based on an equi-molar basis and is similar to
that used for the quantification of the naturally occurring isoflavones in soy flour where
they are normally present as glycosidated compounds (isoflavones conjugated with sugars)
but only standards for the free isoflavones are readily available. It has been demonstrated
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1402 SOMMANO, CAFFIN, AND KERVEN
Figure 3 Mass scans of anthocyanin peaks in Davidson’s plum extract. All run at Cone voltage 25 V.
that the UV absorbance of the free isoflavones are equivalent on a molar basis to the cor-
responding glycosidated compounds.
[21]
The detector response factors were found to be
similar for cyanidin and delphinidin but different for pelargonidin. In the absence of ref-
erence anthocyanidins for the other compounds identified an average response factor for
cyanidin and delphinidin was used to quantify the peak areas for all anthocyanins present.
Table 4 showed the relative proportion of anthocyanins in Davidson’s plum. The
highest proportion shared between Delphinidin and Cyanidin attached with the same sugar
molecule (Hexose–pentose). Petunidin-hexose-pentose, Peonidin-hexose, and malvidin-
hexose were found to be relatively the same amount. Only a little palargonidin-hexose was
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AUSTRALIAN NATIVE FOOD PLANTS 1403
Figure 4 Chromatogram of anthocyanidin standards. Delphinidin RT 15.20 min, Cyanidin RT 16.90 min, and
Pelargonidin RT 18.13 min.
found in Davidson’s plum. To compare with the other fruits, blueberries and cherries also
contain anthocyanins. Malvidin, delphinidin, and cyanidin were the three most identified
compounds. Further development work may be undertaken to use the integrated peak areas
for each of the anthocyanidin M
+
in SIM Mode run under Cone voltage conditions to fully
fragment the anthocyanins to the anthocyanidins.
CONCLUSION
The antioxidant activity conveying by two different methods (DPPH radical and
TEAC) were compared, and it was found that there was an incremental correlation between
the methods. Kakadu plum gave a high level of antioxidant activity by both methods
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1404 SOMMANO, CAFFIN, AND KERVEN
Figure 5 Chromatogram of Davidson’s plum extract.Traces for ESI+ and PDA at 525 nm.
Tab le 4 Anthocyanins identified in Davidson’s plum.
RT (min) M
+
Ion (m/z) Name
Parent anthocyanin
ion
Relative proportion
(%)
10.60 303 Delphinidin-hexose-
pentose
597 30.1
12.41 287 Cyanidin-hexose-pentose 581 30.6
13.11 317 Petunidin-hexose-pentose 611 15.0
13.80 271 Pelargonidin-hexose 433 0.7
14.65 301 Peonidin-hexose 463 12.6
15.20 331 Malvidin-hexose 493 10.9
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AUSTRALIAN NATIVE FOOD PLANTS 1405
because of the high content of ascorbic acid, which reacts rapidly against DPPH radical.
Davidson’s plum showed the lowest antioxidant activity for both techniques as the purple
pigment interferes with activity absorption reading. The study of the effect of time on the
suppression of ABTS radical for TEAC assay showed that the absorbance at 734 nm of all
samples was stable after 10 min, and thus, it was used for calculation of the percentage of
exhibition.
Selected bush plants were also tested for total poly phenol content. There was a nega-
tive correlation between antioxidant capacity by both techniques and total phenols content.
In contrast, Davidson’s plum gave the highest amount of total phenolic content. This can
be elucidated that further investigation on flavonoid and anthocyanin was required.
Some flavonoids were found in the bush plants, which may also perform as natu-
ral antioxidants. The anthocyanins in Davidson’s plum test gave the relative proportion
of the anthocyanins. Delphinidin-hexose-pentose was predominantly found in Davidson’s
plum. Overall, Australian native plants tested contain promising antioxidant levels as well
as the variety of flavonoids, which could be used as functional ingredients in processed
food. Further direction was to study the stability of these bioactive compounds during food
processing.
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