J. Agric. Food Chem. 2006, 54, 1271−1276
1271
Polyphenol Composition and Antioxidant Activity of Kei-Apple
(Dovyalis caffra) Juice
DU TOIT LOOTS,*,† FRANCOIS H.
VAN DER
WESTHUIZEN,‡
AND JOHANN JERLING†
School of Physiology, Nutrition and Consumer Science and School for Chemistry and Biochemistry,
North-West University, Potchefstroom Campus, Private Bag X6001, Potchefstroom 2520, South Africa
The polyphenolic and ascorbate (ASC) components as well as the antioxidant capacity of Kei-apple
(Dovyalis caffra) juice were analyzed and compared to three other fruit juices. The Kei-apple juice
had significantly the highest total polyphenolic concentrations (1013 mg gallic acid equivalent/L),
and solid phase (C18) fractionation identified the majority of these polyphenols to be phenolic acids.
The Kei-apple juice also had significantly the highest ASC concentrations (658 mg/L), which showed
exceptional heat stability with very little conversion to dehydroascorbate (DHA). Antioxidant capacities
of both the unfractionated fruit juices and their solid phase-extracted fractions, as determined by
oxygen radical absorbance capacity and ferric reducing antioxidant power analyses, correlated well
to the polyphenol concentrations. Gas chromatography-mass spectrometry analyses showed caffeic
acid as the most abundant polyphenol present (128.7 mg/L) in the Kei-apple juice; it contributed to
63% of the total antioxidant capacity (of all of the individual compounds identified). Other notable
polyphenols identified in higher concentrations included p-coumaric acid, p-hydroxyphenylacetic acid,
and protocatechuic acid. Our results therefore support the putative high antioxidant value linked to
this fruit and better define this potential in terms of the major antioxidants that exist in the Kei-apple.
KEYWORDS: Kei-apple; Dovyalis caffra; antioxidant; polyphenols; ascorbate; GC-MS; ORAC; FRAP
INTRODUCTION
Polyphenols in foods have recently gained much attention,
because of, among others, their antioxidant functions and their
possible impact on human health. This is demonstrated by
reports of their biological activity in cancer, cardiovascular
diseases, and neurodegeneration (1). Berries and fruits contain
a wide range of flavonoids and phenolic acids that show
antioxidant activity. Flavonoid subgroups in fruits are anthocyanidins, flavonols, flavones, catechins, and flavanones (2).
Phenolic acids occur as hydroxylated derivatives of benzoic acid
and cinnamic acid (3). Many of these polyphenols have redox
properties allowing them to act as reducing agents, hydrogen
donors, and singlet oxygen quenchers (4) and thus contribute
to the antioxidant capacity of teas, wines, and a range of fruits
and vegetables (5, 6). Because of the beneficial effects attributed
to polyphenols (7, 8), there is new interest in finding vegetal
species with high antioxidant content and relevant biological
activity (9).
The Kei-apple (DoVyalis caffra) is native to the Kei River
region of southwestern Africa. It also grows abundantly and
wild in the eastern regions of South Africa. The nearly-round
bright yellow fruit has a tough skin and an apricot-textured,
* To whom correspondence should be addressed. Tel: +27-18-299-2469.
Fax: +27-18-299-2466. E-mail: vgedtl@puk.ac.za.
† School of Physiology, Nutrition and Consumer Science.
‡ School for Chemistry and Biochemistry.
juicy, highly acidic flesh with 5-15 seeds arranged in double
rings in the center. Very little is known about the nutritional
value of this fruit. It has, however, been reported to be rich in
ascorbic acid (AA) (83 mg/100 g) and consists of 3.7% pectin
(10). Additionally, the fruit has a frank taste and is subsequently
thought to be rich in polyphenolic compounds, but no quantification of these has yet been reported.
In this study, we investigated and report the major compounds
associated with antioxidant function in Kei-apple juice. This
was done by evaluating the polyphenol and ascorbate (ASC)
content, as well as the total antioxidant capacity of unfractionated and C18-fractionated Kei-apple juice, and comparing these
data with that obtained from three commonly used fruit juices,
known to have a relatively high polyphenol and/or ASC content.
We additionally report a more detailed characterization of the
individual polyphenol components of the Kei-apple juice and
discuss the possible health benefits of these.
MATERIALS AND METHODS
Preparation of Fruit Juices. Fruit juices were prepared from 100
Kei-apples randomly selected from a larger batch of 500 kg picked in
the month of November from the Bloemhof area in South Africa. The
other fruits used in the comparison were purchased from various South
African fresh produce market places and included 100 strawberries,
200 red globe grapes, and 50 Valencia oranges. All fruits were
immediately frozen at -85 °C until juice preparation. Small scale juice
10.1021/jf052697j CCC: $33.50 © 2006 American Chemical Society
Published on Web 01/26/2006
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Loots et al.
Table 1. Total Polyphenols, Total ASC, ASC, and DHA Concentrations Determined in Kei-Apple, Grape, Strawberry, and Orange Juice
a
juice
total polyphenols
(mg GAE/L)a
total ASC
(mg/L)a
ASC
(mg/L)a
DHA
(mg/L)a
Kei-apple
grape
strawberry
orange
1013 ± 3.0 abc
269 ± 1.4 ad
567 ± 10.1 bde
264 ± 0.9 ce
669 ± 15.7 ab
14 ± 1.4 acd
693 ± 17.7 ce
536 ± 12.83 bde
658 ± 0.7 abc
12 ± 1.2 adf
211 ± 5.3 bde
411 ± 10.2 cee
12 ± 0.2 ab
1 ± 0.1 de
482 ± 11.6 adf
115 ± 2.9 bef
Data presented as means ± standard deviation (n ) 3). Means with a letter in common differ significantly from each other (p < 0.001).
preparation was done via a steam extraction process using a doublejacketed steam kettle. This technique of juice preparation is one of the
many methods used commercially. Various smaller scale models have
been sold for home juice production, which we used to model the large
scale industrial juicing process.
In short, fruits were cut into segments and placed into the kettle.
Oranges were the only fruit to be peeled before the juicing process.
Although this juice extraction method effectively separates the juice
from the other solid components of the fruit, various compounds in
the peels of the oranges affect juice flavor; hence, the peels were
removed before the steaming process (as done by commercial juicers).
The kettle was divided into three levels. The first, uppermost level was
a sieve/strainer onto which the cut fruits were placed. The second
compartment was the juice collection reservoir, which was situated
beneath the sieve, and the third compartment was the water reservoir
used for steam production when heated. The fruit was totally pulped
after 7 min of steaming on a hot plate. The juice was siphoned off
from the juice collection reservoir by a tap for analysis, and the pulp
(peals, seeds, etc.) remained on the sieve in compartment one.
Solid Phase Extraction. Solid phase extractions of the fruit juices
were done on C18 cartridges (Waters) by adapting a method described
by Oszmianski and co-workers (11). This method was based on multiple
elutions at different pH values with three different mobile phases and
results in four fractions containing (i) phenolic acids; (ii) procyanidins,
catechins, and anthocyanin monomers; (iii) flavonols; and (iv) anthocyanin polymers. Briefly, 1 mL of sample was introduced into
preconditioned C18 cartridges and the various fractions eluted at the
specified pH values using 5 mL of the described elution solvents (11).
Determination of Total Polyphenols. The total polyphenol content
in the fruit juices and fruit juices fractions was determined according
to Folin-Ciocalteu’s method (12). Unfractionated fruit juices were
diluted 62 times prior to analysis and filtered through a Whatman no.
1 filter (Merck). Fractionated samples were used as collected from solid
phase extraction. Samples (200 µL) were introduced into test tubes
followed by 1 mL of Folin-Ciocalteu’s reagent (Sigma). This was
allowed to stand for 8 min at room temperature. Next, 0.8 mL of sodium
carbonate (7.5%) was added, mixed, and allowed to stand for 30 min.
Absorption was measured at 765 nm (Shimadzu UV-vis 1601
spectrophotometer). The total phenolic content was expressed as gallic
acid (Aldrich) equivalents (GAE) in milligrams per liter (mg/L).
Because total AA and sugars contribute to the response of the FolinCiocalteu assay, corrections for these were done as described by Asami
et al. (13) and Slinkard et al. (14), respectively. Mean values of
polyphenol content were expressed as GAE/L ( standard deviation (n
) 3).
ASC Determination. ASC, dehydroascorbate (DHA), and total ASC
(ASC + DHA) concentrations were determined in the fruit juices
spectrophotometrically at 578 nm using a method described by Beutler
(15). These measurements were necessary not only for the nutritional
evaluation of the juice but also for correction of the polyphenol
concentrations determined by the Folin-Ciocalteu assay. Mean values
of ASC content were expressed as milligrams per liter (mg/L) (
standard deviation (n ) 3).
Total Sugar Determination. Total sugars were determined in fruit
juices according to the 16th edition of the Official Methods of Analysis
of the Association of Official Analytical Chemists (AOAC) International
(16). The sugar content for strawberry, orange, grape, and Kei-apple
juices was 6, 12, 17, and 5%, respectively, and the values were used
for the corrections for polyphenol concentrations determined via the
Folin-Ciocalteu assay.
Oxygen Radical Absorbance Capacity (ORAC). The fruit juices
were prepared as described earlier and further extractions as well as
ORAC antioxidant capacity analyses of hydrophilic and lipophilic
compounds were performed essentially as described by Prior et al. (17).
The analysis of lipophilic compounds was aided by addition of randomly
methylated β-cyclodextrin, kindly provided by Dr. Ronald Prior, as a
solubility enhancer as described by Huang et al. (18). Briefly, the assay
in a volume of 200 µL contained fluorescein (56 nM) as a target for
free radical attack by 2,2′-azobis(2-amidino-propane) dihydrochloride
(240 mM). A BioTEK fluorescence plate reader was used, and the decay
of fluorescence of fluorescein (excitation, 485 nm; emission, 520 nm)
was measured every 5 min for 2 h at 37 °C. Costar black opaque (96
well) plates were used in the assays. Trolox was used as a standard at
a range between 0 and 20 µM with a polynomial (2nd order) curve fit
analysis. Mean values of antioxidant capacities were expressed as mmol
Trolox equivalents (TE) per liter of the extracts ( standard deviation
(n ) 3).
Ferric Reducing Antioxidant Power (FRAP). FRAP values were
determined essentially as described before (19). Briefly, the reduction
of an Fe3+-2,3,5-triphenyltetrazolium complex in the assay by the
antioxidants in the samples was monitored at 593 nm. L-AA was used
as standard and the FRAP of the samples was expressed as mean
µmol/L AA equivalents (µM AA) ( standard deviation (n ) 3).
Gas Chromatography-Mass Spectrometry (GC-MS) Analysis.
Kei-apple juice extraction and derivatization were carried out as
previously described (20) and analyzed in triplicate. An Agilent 6890
GC ported to a 5973 mass selective detector (CA) was used for
identification and quantification of individual polyphenols. For the
acquisition of an electron ionization mass spectrum, an ion source
temperature of 200 °C and an electron energy of 70 eV were used.
The gas chromatograph was equipped with a SE-30 capillary column,
a split/splitless injection piece (250 °C), and a direct GC-MS coupling
(260 °C). The 10:1 split injection (0.6 µL) was used during the MS
analysis. Helium (1 mL/min) was used as the carrier gas. An oven
temperature of 100 °C, isometric for 1 min, was used as an initial
temperature after which a rise of 10 °C/min was continued until a
temperature of 200 °C was reached. This was followed by a temperature
increase of 15 °C/min until a final temperature of 300 °C was reached.
This temperature was then maintained for a further 5 min.
Statistical Analyses. Descriptive and other statistics were done using
Statistica (StatSoft Inc., United States). To determine whether differences existed between the various fruits, analysis of variation was
performed using the Tukey honest significant difference test for posthoc
comparison. ORAC, FRAP, and polyphenol Pearson correlation
analyses were performed using Statistica (Statsoft Inc., Tulsa, OK) with
significance set at p e 0.05.
RESULTS
Total Polyphenols and ASC. The total polyphenols (mg
GAE/L) and ASC values (mg/L) of the various fruit juices are
given in Table 1. The Kei-apple juice has a significantly higher
amount of total polyphenols (1013 mg GAE/L) as compared to
the other juices prepared under identical conditions. The total
ASC concentration of the Kei-apple juice is comparable to that
of strawberry and more than 100 mg/L greater than that of
orange juice. Interestingly, the ASC in Kei-apple juice is
significantly higher than any of the other juices, with a
comparable low DHA content.
J. Agric. Food Chem., Vol. 54, No. 4, 2006
Polyphenol Composition and Antioxidant Activity of Kei-Apple
1273
Table 2. Concentrations of Various Solid Phase C18 Polyphenol Fractions of Kei-Apple, Grape, Strawberry, and Orange Juices Determined by the
Folin−Ciocalteu Method
a
juice
phenolic acids
(mg GAE/L)a
procyanidins, catechins,
and anthocyanin
monomers (mg GAE/L)a
flavonols
(mg GAE/L)a
anthocyanin
polymers
(mg GAE/L)a
Kei-apple
grape
strawberry
orange
495.5 ± 16.3 abc
73.0 ± 5.2 a
86.0 ± 5.7 b
68.3 ± 2.3 c
214.9 ± 5.7 abd
101.9 ± 2.4 acf
282.0 ± 7.2 bcg
75.7 ± 0.2 dfg
13.0 ± 2.0 abd
29.6 ± 0.4 acf
34.1 ± 1.6 bce
50.5 ± 1.5 dfe
23.7 ± 0.3 bde
27.8 ± 2.6 cef
51.3 ± 0.5 bcg
41.7 ± 1.2 dfg
Data presented as means ± standard deviation (n ) 3). Means with a letter in common differ significantly from each other (p < 0.001); e (p ) 0.03).
Table 3. ORAC of Fruit Juices
juice
total
(mM TE)a
phenolic acids
(mM TE)a
procyanidins, catechins,
and anthocyanin
monomers (mM TE)a
flavonols
(mM TE)a
anthocyanin
polymers
(mM TE)a
Kei-apple
grape
strawberry
orange
43.9 ± 1.3 abc
15.7 ± 0.7 ade
33.0 ± 2.6 bdi
21.6 ± 1.4 cei
17.4± 1.0 abc
5.1 ± 1.6 af
10.3 ± 0.4 bef
4.1 ± 0.1 ce
12.3 ± 1.9 ab
5.8 ± 1.1 adg
13.2 ± 0.5 dh
2.0 ± 0.01 bgh
5.4 ± 0.1
0.9 ± 0.3
2.6 ± 0.6
1.1 ± 0.1
2.2 ± 0.2 ab
1.4 ± 0.01 dh
4.2 ± 0.7 acd
7.7 ± 0.3 bch
a Data presented as means ± standard deviation (n ) 3); mM TE, mmol/L TEs. Means with a letter in common differ significantly from each other (p < 0.002); g (p )
0.004); e (p ) 0.01); and f (p ) 0.04).
Table 4. FRAP of Fruit Juices
juice
total
(µM AA)a
phenolic acids
(µM AA)a
procyanidins, catechins,
and anthocyanin
monomers (µM AA)a
flavonols
(µM AA)a
anthocyanin
polymers
(µM AA)a
Kei-apple
grape
strawberry
orange
6100 ± 191 abc
1514 ± 61 ade
3517 ± 179 bdf
2253 ± 111 cef
2270.7 ± 26.5 abc
90.8 ± 17.4 ad
416.2 ± 40.2 bdf
97.8 ± 19.5 cf
566.4 ± 26.7 a
461.4 ± 13.4 b
1545.1 ± 88.3 abd
563.2 ± 51.6 d
109.9 ± 6.6 bc
97.7 ± 1.9 de
21.0 ± 10.6 bdf
65.6 ± 9.4 cef
82.6 ± 7.6
0.6 ± 0.2
92.1± 18.1
22.1 ± 1.2
a Data presented as means ± standard deviation (n ) 3); µM AA, µmol/L AA equivalents. Means with a letter in common differ significantly from each other (p < 0.001);
e (p ) 0.004).
Polyphenol Fractionation. Solid phase (C18) fractionation
of the juices (Table 2) shows the Kei-apple juice phenolic acids
to contribute to 66.3% of the total of the combined fractions,
followed by the procyanidin, catechin, and anthocyanin monomers (28,8%) and then by anthocyanin polymers (3.2%) and
flavonols (1.7%). Comparative to the other juices, the Kei-apple
juice had significantly higher phenolic acids (approximately
seven times more than other juices) and a relatively high
procyanidin, catechin, and anthocyanin monomer fraction, which
is comparable to that detected in strawberry juice. Its flavonols
and anthocyanidin polymer content are, however, significantly
the lowest of all of the juices used in the comparison, with
orange juice having the highest flavonols and strawberry juice
the highest anthocyanidin polymers.
Antioxidant Capacity. Antioxidant capacity of the various
fruit juices and their fractions were determined by ORAC and
FRAP analyses and summarized in Tables 3 and 4, respectively.
The Kei-apple juice showed both significantly higher total
ORAC and FRAP values as compared to the other fruits juices.
In both assays, the decreasing order of total antioxidant capacity
values was as follows: kei-apple, strawberry, orange, and grape
juice. ORAC and FRAP analyses of the fractionated samples
indicate that the Kei-apple juice phenolic acid fraction is the
highest contributor of its total antioxidant capacity, followed
by the procyanidin, catechin, anthocyanin fraction > flavonol
> anthocyanin polymers. This is notably different from the three
other juices where the procyanidin, catechin, and anthocyanin
fractions were the highest contributors to antioxidant capacity,
with the exception of the anthocyanin polymer fraction in orange
juice.
GC-MS Polyphenol Characterization of Kei-Apple Juice.
GC-MS is particularly suited for determining nonflavoniod
components, which were identified by C18 fractionation to be
the major components of the Kei-apple juice. Flavonoid
components of molecular weights below 800 are also easily
detected using this technique. A summary of the polyphenol
compounds in the Kei-apple juice sample as identified by GCMS is given in Table 5. Using the published Trolox equivalent
antioxidant capacity (TEAC) of the various compounds, the
contribution of individual polyphenols to the total antioxidant
activity (TAA) of the sample was calculated (4, 21).
Caffeic acid was by far the most prominent polyphenol
present in the Kei-apple juice (128.7 mg/L). The order of other
predominant nonflavonoid components was p-coumaric acid >
p-hydroxyphenylacetic acid > protocatechuic acid > 3-methoxy4-hydroxyphenylacetic acid. When considering the antioxidant
potential of these compounds using their TEAC values, again
caffeic acid predominates due to its high concentrations (alone
contributing to 63% of the total TAA of the GC-MS identified
polyphenols). This was followed by p-coumaric acid > protocatechuic acid > 3-methoxy-4-hydroxyphenylacetic acid. Although gallic acid was detected at much lower concentrations,
it is also a major contributor to the TAA of the mixture due to
its high antioxidant capacity.
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J. Agric. Food Chem., Vol. 54, No. 4, 2006
Loots et al.
Table 5. GC-MS Polyphenol Content, TEAC, and TAA of Kei-Apple Juicea
class
hydoxybenzioic acids
hydroxycinnamic acids
hydroxyhydrocinnamic acids
hydroxyphenylacetic acids
compound
nonflavonoids
salicylic acid
m-hydroxybenzoic acid
vanillic acid
gallic acid
R-resorcylic acid
protocatechuic acid
syringic
m-coumaric acid
p-coumaric acid
ferulic acid
caffeic acid
hydro-p-coumaric acid
p-hydroxyphenylacetic acid
3-methoxy-4-hydroxyphenylacetic acid
flavonoids
catechins
a
catechin
concn
(mg/L)
TEAC
(mM)b
TAA
(µM)c
0.35 ± 0.02
4.27 ± 0.12
3.64 ± 0.35
2.36 ± 0.11
0.57 ± 0.02
9.51± 0.13
0.66 ± 0.03
1.67 ± 0.02
15.70 ± 0.30
0.81 ± 0.02
128.7 ± 1.03
0.35 ± 0.04
10.62 ± 0.62
6.24 ± 0.11
0.04
0.84
1.43
3.01
2.15
1.19
1.36
1.21
2.22
1.91
1.26
d
0.34
1.72
0.10 ± 0.005
25.76 ± 0.07
31.01 ± 3.0
41.74 ± 1.98
5.44 ± 0.22
73.48 ± 1.01
4.93 ± 0.25
12.29 ± 0.12
212.5 ± 4.0
7.98 ± 0.19
900.8 ± 7.19
d
23.76 ± 1.38
58.94 ± 1.0
2.71 ± 0.02
2.4
22.49 ± 0.18
Concn, concentration expressed as mean ± standard deviation (n ) 3). b Ref 4. c TAA determine by calculation (4). d Data unavailable.
Correlation Analyses. Comparing the unfractionated fruit
juice samples, ORAC (r ) 0.95) and FRAP (r ) 0.98) both
correlated significantly with the polyphenol content. In the
fractionated samples, slightly lower ORAC and FRAP correlations with polyphenols were observed (r ) 0.87 and 0.96,
respectively); however, they were still highly significant (p e
0.05). To compare the two methods used for determining
antioxidant capacity, all ORAC and FRAP values were compared and showed significant correlations (r ) 0.97).
DISCUSSION
Over the past 10 years, there has been a growing interest in
the value of polyphenols among researchers and food manufacturers. This is mainly because of their antioxidant properties,
their abundance in our diet, and their probable role in the
prevention of various diseases associated with oxidative stress,
such as cancer, cardiovascular disease, and neurodegeneration
(22). The Kei-apple is a fruit that has been associated with high
antioxidant properties, although little scientific data exists to
support anecdotal reports. In this study, we investigated the
major compounds associated with the antioxidant potential in
the fruit juice. Total polyphenol and ASC content of the Keiapple juice was determined and antioxidant capacities evaluated
using two separate techniques. To better interpret the data
obtained from the Kei-apple juice, we compared these values
with that of three commonly used fruit juices.
The total polyphenol content of the Kei-apple juice was
almost twice that of strawberry juice and almost four times that
of grape and orange juice. The low polyphenol content of the
grape juice can be attributed to the fact that ∼70% of its total
polyphenol content occurs in the seeds and the majority of the
remaining ∼30% occurs in the peel (23). Both of these fruit
components are excluded during the juicing process. The total
ASC content of the Kei-apple juice compared well to that of
strawberries and was 100 mg/L more than that of orange juice.
Of particular interest, however, was that the Kei-apple juice ASC
showed exceptional stability with very little oxidation to DHA.
This is of particular importance to both health and industry.
Although DHA is easily taken up by erythrocytes and other
cells in vivo and reduced to ASC, which is the active form of
vitamin C (24), it is not readily absorbed across the intestinal
mucosa (25) and has little antiscorbutic activity (26).
The crude polyphenol composition of the various fruit juices
was compared by C18 fractionation. The majority of the
polyphenols in the Kei-apple juice was identified as phenolic
acids, followed by procyanidins, catechins, and anthocyanin
monomers > anthocyanin polymers > flavonols. This is in line
with a report by Miller et al. associating acidic fruits with a
high phenolic content (27). The low flavonol content of the
grape juice can be attributed to the fact that these polyphenols
are concentrated in the seeds of these fruits (23), which are
excluded in the juicing method. High concentrations of polyphenols were measured in the strawberry juice fractions containing
anthocyanins, which are associated with the rich red color seen
in these fractions (28).
Both the ORAC and the FRAP analyses of the unfractionated
fruit juices showed that, in comparison to the other juices
included in this study, Kei-apple juice has a significantly higher
antioxidant capacity. It has been reported that total polyphenol
content correlates well with antioxidant capacity (29). This high
correlation of ORAC and FRAP analyses with the polyphenol
concentration of the unfractionated samples was indeed also
observed in our study (r ) 0.95 and r ) 0.98, respectively).
The amount of polyphenols is, however, not the only factor
influencing antioxidant capacity. The structural arrangements
(number and position of hydroxyl groups, double bonds, and
aromatic rings) of the various individual polyphenols also play
a role (4). This would explain some of the slightly lower
correlations observed with ORAC or FRAP and polyphenol
content correlation analyses (r ) 0.87 and r ) 0.96, respectively) for the fractionated fruit juice samples. An example of
these variations is the higher ORAC value in the Kei-apple
flavonol fraction (Table 3) despite it having the lowest
concentration (Table 2) as compared to the same fraction of
the other fruit juices. A similar anomaly can be seen in the
anthocyanin polymer fraction of orange juice. Another clear
correlation was obtained when comparing all ORAC and FRAP
values for the combined samples (r ) 0.97), indicating both
ORAC and FRAP to be good predictors for measuring antioxidant capacity. Similar correlations are reported by Moyer et al.
(29). Ou et al. (30), however, showed discrepancies in these
comparisons with certain fruit and vegetables showing exceptionally good correlations and others showing the opposite. In
our study, trend outliers showing a higher FRAP and a lower
Polyphenol Composition and Antioxidant Activity of Kei-Apple
ORAC value (Kei-apple phenolic acid and orange juice flanonol
fractions) or a higher ORAC and a lower FRAP value (orange
juice anthocyanin polymer fraction) may be attributed to the
varying composition of the individual components of these
fractions. As the FRAP value is an indication of the ferric ion
reducing power of the mixture and the ORAC value indicates
ability to scavenge free radicals, the various individual polyphenol components of the mixture may have stronger free radical
scavenging abilities than a ferric ion reducing power or visa
versa.
Further characterization of the individual polyphenols components by GC-MS showed caffeic acid to be the most
prominent compound contributing to 63% of the TAA of all of
the individual compounds identified using this technique. Caffeic
acid, in addition to other polyphenols, has been associated in
the possible preventions of cancer, cardiovascular disease, and
neurodegeneration. It has been reported to inhibit the growth
of human-derived breast and colon cancer cells (31). Cancer is
a hyperproliferative disorder, in which invasion and angiogenesis, leading to tumor metastasis by the activation of nuclear
transcription factor κΒ (NF-κB) occurs (32). There are various
mechanisms by which caffeic acid may exert its proposed health
benefits. It is seen to have a direct interaction with the aryl
hydrocarbon receptors, nitric oxide inhibition, and proapoptotic
effects in cancer cells (31), and it has been shown to inhibit
tumor cell invasion and metastasis by the inhibition of methalloproteinase-2 and -9 (33). Caffeic acid has also been reported
to protect DNA against damage by nitrite and proxynitrite (34).
Furthermore, it is thought to promote health due to its antioxidant effects. It is seen to strongly inhibit lipid hydroperoxide
formation, lipid hydroperoxide formation, and aqueous peroxyl
radical-induced oxidation of low-density lipoproteins while
sparing R-tocopherol (35). Apart from being able to act as a
free radical scavenger, caffeic acid is shown to inhibit monoamine oxidase (36) and 5-lipoxygenase (37) implicated in
various neurodegenerative diseases.
Although the results indicate caffeic acid to be by far the
most predominant polyphenol component of Kei-apple juice,
the other polyphenol components occurring also contribute to
possible health-promoting effects of this juice. It is well-known
that the protective health benefits of polyphenols are mainly
through a combination of additive and/or synergistic effects (38).
Additionally, other polyphenol compounds, which were detected
in the Kei-apple juice, have also been associated with various
beneficial health effects (1) and, although these occur in lower
concentrations, may also prove to be beneficial.
From this study, we conclude that Kei-apple juice is a rich
source of plant-derived antioxidant compounds (polyphenols and
vitamin C) with strong antioxidant capacity, which is generally
associated with health-promoting properties. Although the plant
is not widely known or cultivated, it may be an interesting
alternative natural source of these compounds.
ABBREVIATIONS USED
ASC, ascorbate; DHA, dehydroascorbate; ORAC, oxygen
radical absorbance capacity; FRAP, ferric reducing antioxidant
power; GC-MS, gas chromatography-mass spectrometry; GAE,
gallic acid equivalents; AOAC, Association of Official Analytical Chemists, TE, trolox equivalent; AA, ascorbic acid; TEAC,
trolox equivalent antioxidant capacity; TAA, total antioxidant
activity.
ACKNOWLEDGMENT
We thank the following institutions and persons for their kind
contributions: Dr. Ronald Prior for kindly donating the ran-
J. Agric. Food Chem., Vol. 54, No. 4, 2006
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domly methylated β-cyclodextrin for the ORAC analyses and
Chricilia Visser at J. Muller Laboratories (PTY) Ltd. (Cape
Town, South Africa) for sugar analyses.
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Received for review October 31, 2005. Revised manuscript received
December 5, 2005. Accepted December 6, 2005.
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