Available via license: CC BY 4.0
Content may be subject to copyright.
Food and Nutrition Sciences, 2018, 9, 1273-1284
http://www.scirp.org/journal/fns
ISSN Online: 2157-9458
ISSN Print: 2157-944X
DOI:
10.4236/fns.2018.911091 Nov. 12, 2018 1273 Food and Nutrition Sciences
Antioxidant Activity of Methoxylated
Flavonoids in Oils in Deep Frying Processes
Onesmus Maina Wanjau1*, Symon Maina Mahungu2, Josphat Clement Matasyoh1
1Department of Chemistry, Faculty of Science, Egerton University, Nakuru, Kenya
2Deparment of Dairy and Food Science, Faculty of Agriculture, Egerton University, Nakuru, Kenya
Abstract
Methoxylated flavonoids isolated from cold acetone leaf wash of
Polygonum
senegalense
; 5-hydroxy-7-methoxyflavanone 1 and 5-hydroxy-6,7-dimethoxy-
flavanone 3, were tested for their ability to enhance thermal stability of veg-
etable oils. Determination of the peroxide value (P.V.) and the
p
-
Anisidine
value (
p
-
A.V.) was done according to the standard methods of analysis. The
compounds were tested for
in vitro
cytotoxicity against
a mammalian
cell-line, Chinese Hamster Ovarian (CHO) using the 3-(4,5-dimethylthiazole-
2-yl)-2,5-diphenyltetrazoliumbromide (MTT)-
assay. Studies on changes in
peroxide and
p
-
Anisidine values for the oils heated to temperatures between
180˚C and 200˚C recorded better stability enhancement at 100 ppm concen-
tration with these flavonoids than the commercial antioxidant, butylated hy-
droxytoluene (BHT). The plant-based flavonoids
had no significant cytotoxic
effect against the CHO cell-line and may serve as alternative antioxida
nts to
synthetic ones which have previously raised great concern over the health of
consumers.
Keywords
Polygonum senegalense,
Antioxidant Activity, Methoxylated Flavonoids,
Vegetable Oils, Cytotoxic Effect
1. Introduction
Stability enhancement of fish oil is necessary to improve its shelf-life because
fish oil contains highly unsaturated oils which are more susceptible to oxidation
[1]. The rate and extent of formation of oxidation products in oils depends on
the nature of the fatty acid composition (monounsaturated or polyunsaturated),
the temperature at which the oil is heated [2] and the presence of metal ions [3]
How to cite this paper:
Wanjau, O.M.,
Mahungu, S
.M. and Matasyoh, J.C. (2018
)
Antioxidant Activity of
Methoxylated Fla-
vonoids in Oils in Deep Frying Processes.
Food and Nutrition Sciences
,
9
, 1273-1284.
https://doi.org/10.4236/fns.2018.911091
Received:
August 30, 2018
Accepted:
November 9, 2018
Published:
November 12, 2018
Copyright © 201
8 by authors and
Scientific
Research Publishing Inc.
This work is licensed under the Creative
Commons Attribution International
License (CC BY
4.0).
http://creativecommons.org/licenses/by/4.0/
Open Access
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1274 Food and Nutrition Sciences
[4]). Fish oil largely comprises of arachidonic acid, C20:4ω-6, docosapentaenoic
acid, C22:5ω-3, and docosahexaenoic acid, C22:6ω-3 [5] and is more easily oxi-
dized than vegetable oil [6]. Lipid oxidation is a highly deteriorative process and
health disorders such as atherosclerosis and cancerogenesis among others corre-
late highly to the consumption of highly oxidized oils [7].
Edible fats/oils may contain up to 200 ppm of synthetic antioxidants, such as
butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT) [8], pur-
posely added to improve the shelf life of the edible fats/oils. The use of synthetic
antioxidants is, however limited, because of their physical characteristics and the
unfolding toxicological concerns on some of the synthetic antioxidants [9].
Flavonoid aglycones are reported to be deposited on the surface of leaves,
twigs and seeds of
Polygonum senegalense
and
Psiadia punctulata,
with a higher
deposition on younger plant parts than on the older parts [10] [11]). The exis-
tence of an exudate on the leaf surface, rich in methoxylated flavonoids [12]
[13]), is fascinating. The constituent compounds of leaf surface exudates [14]
supposedly serve some protective role on the plant [15]). Epicuticular layer and
external flavonoids not only reflect radiation, but are also known to be good
quenchers of singlet oxygen [16]. Some of the constituent compounds of the leaf
surface exudates are relatively non-polar and could perhaps be endowed with
invaluable bioactivity in the relatively non-polar fish oil and edible oils. The
choice for an oil stability enhancer must critically address the solubility and
thermal stability of the oil additive and evaluate their cytotoxicity levels.
The presence of some synthetic antioxidants in fats and oils may not guaran-
tee stability at deep frying temperatures. Antioxidants of low boiling point may
gradually vaporize and thus expose the oil to oxidation [17]. The oil may dege-
nerate into various oxidation products, some of which may have injurious effects
to the body. Antioxidant principles, stable at high temperatures, must be identi-
fied for use as oil additives to fortify the heat stability of the oils. The concentra-
tion levels of antioxidants may continue to diminish through vaporization at the
high temperatures, leaving the oil exposed to further oxidation [18].
2. Materials and Methods
2.1. Plant Materials
The resinous leafy branches of
P. senegalense
were harvested, along the river
banks of Njoro river within Egerton University, Nakuru County, Kenya, at an al-
titude of 2300 m, twenty five kilometers, west of Nakuru town. A voucher spe-
cimen is deposited in the National Museum of Kenya Herbarium.
2.2. Extraction
One kilogram of leaves detached from the branches of
P. senegalense
plant were
stuffed into a 5 L erlmeyer flask for extraction. A 1.5 liter portion of acetone was
introduced into the flask and shaken for two minutes and decanted as an orange
solution [19] two more fresh portions of acetone were used to wash the leaves
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1275 Food and Nutrition Sciences
clear of the orange exudate. The acetone extract was decanted and filtered
through a filter paper into a 2.5 L brown glass bottle. The acetone was recovered
using a rotary evaporator at a rotate speed of 100, heated at a water bath regu-
lated at 60˚C. The concentrate was preserved in an open brown glass bottle (100
ml) and stored in a vacuum desiccator until it gave a constant mass of 47.5 g (
i.e.
20.2% of dry leaves) on weighing.
2.3. Chromatographic Methods
20 g of the extract was introduced into a glass column (4 cm diameter), packed
with 129 g of 230 - 400 mesh silica gel. The column was sequentially eluted with
500 ml portions of hexane, 40% CH2Cl2 in hexane and finally with 60% CH2Cl2
in hexane, effectively eluting four coloured bands ranging from yellow to red.
The eluant was collected as 40 ml fractions from which pure compounds were
isolated through fractional crystallization from dichloromethane-methanol
mixtures. Melting points (uncorrected), were determined using a Gallen camp
melting point apparatus. 1H and 13C NMR spectra were determined at 500 and
125 MHZ, respectively.
Identification of the compounds was achieved through correlation of spectral
data, melting point values and comparison with literature data [20].
2.4. Determination of Peroxide and p-Anisidine Values
Sunflower and rapeseed oils and fractionated palm shortening (Rina oil and
Chipsy fat and Canola oil) were procured locally from local market in Nakuru.
Two aluminium based cooking pots (15 cm in diameter each) were used for
electrically heating the oil in pot A and B (control) respectively.
250 g of each oil sample was electrically heated in the cooking pots up to a
temperature of 180˚C - 200˚C for 7 hrs each day. 50 mg of the plant isolates were
dissolved in 1 ml of acetone in a vial bottle and introduced into the oil in pot A.
The vial bottle was rinsed twice with 1 ml portions of acetone and the washings
transferred into the oil. The second pot served as a control into which 3 ml of
acetone was added into the oil. Determination of the peroxide value (P.V.) and
the
p
-Anisidine value (
p
-A.V.) was done according to the standard methods of
analysis [21]. The experiment was repeated three times for each case.
2.5. Cytotoxicity Screening Tests
Compounds were tested for
in vitro
cytotoxicity against a mammalian cell-line,
Chinese Hamster Ovarian (CHO) using the 3-(4,5-dimethylthiazole-2-yl)-2,5-
diphenyltetrazoliumbromide (MTT)-assay [22]. All samples were tested in trip-
licate on a single occasion. The MTT-assay is used as a calorimetric assay for
cellular growth and survival, and compares well with other available assays [23]
[24]). The tetrazolium salt MTT was used to measure all growth and chemosen-
sitivity. Flavanone 1 (Polsen 1) was dissolved in 10% methanol while flavanone 3
(polsen 3) was dissolved in 10% DMSO. Compounds were tested as a suspension
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1276 Food and Nutrition Sciences
due to poor solubility. The initial concentration of the stock solutions was 2
mg/ml for all samples. All compounds were stored at −20˚C until testing. Emen-
tine was used as the positive control in all experiments. The initial concentration
of all samples were 100 mg/ml, which was serially diluted in complete medium
with 10-fold dilutions to give 6 concentrations, the lowest being, 0.001 μg/ml.
The 50% inhibitory concentration (IC50) values for these samples were obtained
from dose response curves, using a non-linear dose response curve fitting ana-
lyses via GraphPad Prism v, 4.0 software.
3. Results and Discussion
Column chromatography of the acetone leaf extract using dichlomethane-
hexane solvent system mixtures yielded known methoxylated flavonoids 1 and 3
(Figure 1). 1H NMR and 13C NMR spectra are shown on Figures 2-5.
5-Hydroxy-7-methoxyflavanone 1 was obtained as colourless crystalline
flakes, melting point of 101˚C. The 1H NMR spectrum of 1 showed the presence
of one methoxyl group at δ 3.79. It also exhibited three sets of double doublets of
an AMX system at δ 5.408 (1H, J = 3.0, 10.1 Hz), δ 3.074 (1H, J = 13.0, 4.17 Hz)
and δ 2.81(1H, J = 3.17, 14.08 Hz) which were characteristic of H-2, H-3ax and
H-3eq, respectively, of the ring C of a flavanone moety (Rao
et al
., 2004). Two
meta-coupled doublets, at δ 6.05 and 6.06 (J = 2.38 Hz), each integrating for one
proton, were assigned to H-6 and H-8, respectively. Noesy correlation of the
methoxy group signal to these protons and HMBC correlations assigned the
methoxy group to C-7 (δC 167.98). A D2O exchangeable downfield signal at δ
12.01 (IH) was assigned to a hydrogen-bonded hydroxyl group at C-5 (δC 164)
[25].
5-Hydroxy-6,7-dimethoxyflavanone 3 was obtained as light yellow crystals
(61.9 mg), melting point 147˚C - 148˚C. The flavanone nucleus was confirmed
by the presence in the NMR spectrum of an ABX system centered at δ 2.81, 3.08
and 5.40 for the C-2 and C-3 protons. Signals at δ 3.83 (3H) and 3.86 (3H) were
assigned to a hydrogen bonded OH for C-5, δC 155.0. HMBC correlations of the
signal at δH 11.85 with one of the methoxylated C-atoms (δC 130.6) required the
signal at δH 6.11 to be attached to C-8. A multiplet centered at δH 7.41 (5H) was
attributed to a mono-substituted ring C. Flavanones 1 and 3 have previously
been isolated from
Onychium ciliculosum
, a medicinal herb [26].
Four brands of vegetable oils; Sunflower oil, Canola oil, Rina oil and Chipsy
fat when heated to 180˚C - 200˚C displayed heat instability on assessment of
Figure 1. Flavanones 1 & 3.
1 R6 = H
3 R6 = OMe
O
HO
R
6
MeO
O
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1277 Food and Nutrition Sciences
Figure 2. 1H NMR spectrum.
Figure 3. 13C NMR spectrum.
their patterns in both the
p
-anisidine and the peroxide values as observed in
Figure 6 and Figure 7.
Stability enhancement for these oils was implied based on the continued rise
in peroxide and p-anisidine values for 14 hours on average when flavanones iso-
lated from the
P. senegalense
were introduced into the oils at concentrations of
100 ppm as observed in Figures 8-11.
5-Hydroxy-7-methoxyflavanone suppressed the rise in p-Anisidine values and
the peroxide values respectively and resulted in predictable patterns for all the
oils as observed in Figures 8-11. It also prevented oil browning and registered a
delay in rise in peroxide values, recording a maximum after 14 hours on average.
5-Hydroxy-6,7-dimethoxyflavanone 3 also displayed similar stability enhance-
ment patterns when introduced into Sunflower oil at a concentration of 100 ppm.
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1279 Food and Nutrition Sciences
Figure 6. Changes in p-AV for plain oils heated to 180˚C - 200˚C.
Figure 7. Changes in peroxide values for plain oils heated to 180˚C - 200˚C.
Figure 8. Changes in p-AV values for Oils heated with 100 ppm of 5-hydroxy-7-
methoxyflavanone 1.
0
50
100
150
200
250
0 4 8 12 16 20 24 28 32
p-Anisidine value
Cummulative heating time (hrs)
Commercial oils/ fats heated to 80-200 deg C
Sunfl o wer
Canola
Rina oil
Chipsy
0
5
10
15
20
25
30
0246810 12 14 16 18 20 22 24 26 28 30
Peroxi de Values
Cummulati ve Heating Time (hrs)
Plain oi ls heated to 180-200 deg C
SO p lain
Canola
Rina
Chip sy
0
50
100
150
200
250
300
350
400
0 4 8 12 16 20 24 28 32
p-Anisidine V alues
Cummulati ve heating time (hrs)
Oils heated with 100ppm of compd 1
SO+pols1
CO+pols1
Rina+pols1
SO+BHT
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1280 Food and Nutrition Sciences
Figure 9. Changes in peroxide values for Oils heated with 100 ppm of
5-hydroxy-7-methoxyflavanone 1.
Figure 10. Changes in p-AV values for Sunflower oil heated with 100 ppm of compounds
1 and 3.
Figure 11. Changes in peroxide values for Sunflower oil heated with 100 ppm of com-
pounds 1 and 3.
0
5
10
15
20
25
30
0246810 12 14 16 18 20 22 24 26 28 30
Peroxi de Values
Cummulati ve heating Tim e (Hrs)
Oils heated to 180-200 deg C
SO+pols1
CO+pols1
Rin a+pols1
SO+BHT
0
50
100
150
200
250
300
350
400
04812 16 20 24 28 32
p-Anisidine val ue
Cummulative heating tim e (hrs)
Sunflower oil heated with flavonoids
SO plain
SO+Po l s1
SO+Po l s3
SO+BHT
0
5
10
15
20
25
30
0 4 8 12 16 20 24 28 32
Peroxi de value
Cummulati ve heating time (hrs)
Sunflower oil heated with flavonoids
SO plain
SO+Po l s1
SO+Po l s3
SO+BHT
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1281 Food and Nutrition Sciences
Cytotoxicity Screening Tests
Compounds 1 and 3 had no significant cytotoxic effect against the CHO cell-line
as observed in Table 1 and Figure 12 on dose-response curves.
Figure 12. Dose-response curves of fractions using the CHO cell-line.
Table 1. IC50-values of fractions using the CHO cell-line.
Compound
IC50 (µg/ml)
Polsen 1 (pols 1) >100
Polsen 3 (pols 1) >100
Emetine 0.07
The propensity of a flavonoid to inhibit free-radical mediated events is go-
verned by its chemical structure. The number of substituent groups and their
positions on the flavonoid structure can influence the radical-scavenging activity
[27].
4. Conclusion
The present study indicate that 5-hydroxy-7-methoxyflavanone (pols 1) and
5-hydroxy-6,7-dimethoxyflavanone (pols 3) are effective anti-oxidants in re-
tarding the formation of primary and secondary oxidation products during deep
frying using vegetable oils. The two flavanones had no significant cytotoxic effect
and are therefore potential food additives intended to serve as antioxidant prin-
ciples in oil deep frying processes and in the formulation of animal feeds. The
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1282 Food and Nutrition Sciences
melting points of these flavanones are well above the melting point of BHT
(70˚C).
Acknowledgements
The authors are grateful to the University of Kwa-Zulu Natal and Prof Dulcie
Mullholand for support in laboratory space, chemicals and instruments.
Conflicts of Interest
The authors declare no conflicts of interest regarding the publication of this pa-
per.
References
[1] Honold, P.J., Nouard, M.-L. and Jacobsen, C. (2016) Oxidative Stability during Sto-
rage of Fish Oil from Filleting By-Products of Rainbow Trout (
Oncorhynchus my-
kiss
) Is Largely Independent of the Processing and Production Temperature.
Euro-
pean Journal of Lipid Science and Technology
, 118, 967-973.
https://doi.org/10.1002/ejlt.201500344
[2] Choe, E. and Min, D.B. (2006) Mechanisms and Factors for Edible Oil Oxidation.
Comprehensive Reviews in Food Science and Food Safety
, 5.
[3] Rade, D.,
et al
. (1997) Frying of French Potatoes in Palm Oil and Vegetable Oil.
Food Technology and Biotechnology
, 35, 119-124
[4] Mahungu, S.M., Artz, W.E. and Perkins, E. (1999) Oxidation Products and Meta-
bolic Processes. In: Boskou, D. and Elmadfa, I., Eds.,
Frying of Food
, Technomic
Publishing Company, Inc., Lancaster, 27.
[5] Srigley, C.T. and Rader, J.I. (2014) Content and Composition of Fatty Acids in Ma-
rine Oil Omega-3 Supplements.
Journal of Agricultural and Food Chemistry
, 62,
7268-7278. https://doi.org/10.1021/jf5016973
[6] Bartee, S.D., Kim, H.J. and Min, D.B. (2007)
Effects of Antioxidants on the Oxida-
tive Stability of Oils Containin Arachidonic, Docosapentaenoic and Docosahexae-
noic Acids.
Journal of the American Oil Chemists
’
Society
, 84, 363-368.
https://doi.org/10.1007/s11746-007-1046-4
[7] Anwar, F., Chatha, S.A.S. and Hussain, A.I. (2007) Assessment of Oxidative Deteri-
oration of Soybean Oil at Ambient and Sunlight Storage.
Grasas Y Aceites
, 58,
390-395.
[8] German, J.B. (2002) Antioxidants. In: Larry Branen, A., Michael Davidson, P., Sal-
minen, S. and Thorngate, J.H., Eds.,
Food Additives
, Marcel Dekker, Inc., New
York, 2nd Edition, 528.
[9] Wang, M.F., Li, J.G., Rangarajan, M., Shao, Y., La Voie, E.J., Huang, T.-C. and Ho,
C.-T. (1998) Antioxidative Phenolic Compounds from Sage (
Salvia officinalis
).
Journal of Agricultural and Food Chemistry
, 46, 4869-4873.
https://doi.org/10.1021/jf980614b
[10] Midiwo, J.O., Matasi, J.J., Wanjau, O.M., Mwangi, R.W., Waterman, P.G. and Wol-
lenweber, E. (1990) Anti-Feedant Effects of Surface Accumulated Flavonoids of
Po-
lygonum senegalense
.
Bulletin of the Chemical Society of Ethiopia
, 4, 123-127.
[11] Midiwo, J.O., Gikonyo, N.K., Wanjau, O.M., Matasi, J.J. and Waterman, P.G. (1992)
Flavonoids of
Polygonum senegalense
(Meisn) Part II: More Surface and Internal
Tissue Flavonoid Aglycones.
Bulletin of the Chemical Society of Ethiopia
, 6, 19-122.
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1283 Food and Nutrition Sciences
[12] Ogweno Midiwo, J., Owino, N.O. and Dagne, E. (1994) Flavonoids of Polygonum
Senegalense Part III: Isolation of Dihydrochalcone Glucoside and Quercetin Gluco-
sides.
Bulletin of the Chemical Society of Ethiopia
, 8, 79-84.
[13] Midiwo, J.O., Omoto, F.M., Yenesew, A., Akala, H.M., Wangui, J., Liyala, P., Wa-
sunna, C. and Waters, N.C. (2007) The First 9-Hydroxyhomoisoflavanone, and An-
tiplasmodial Chalcones, from the Aerial Exudates of
Polygonum senegalense
.
ARKIVOC
2007, ix, 21-27.
[14] Juma, B.F., Yenesewa, A., Midiwo, J.O. and Waterman, P.G. (2001) Flavones and
Phenylpropenoids in the Surface Exudates of
Psiadia punctulata. Phytochemistry
,
57, 571-574. https://doi.org/10.1016/S0031-9422(01)00147-9
[15] Midiwo, J.O., Owuo, F.A.O., Juma, B.F. and Waterman, P.G. (1997) Diterpenes
from the Leaf Exudates of
Psiadia punctulata
.
Phytochemistry
, 45, 117-120.
https://doi.org/10.1016/S0031-9422(96)00812-6
[16] Rigotti, A. (2007) Absorption, Transport and Tissue Delivery of Vitamin E.
Mole-
cular Aspects of Medicine
, 2, 423-436. https://doi.org/10.1016/j.mam.2007.01.002
[17] Alakali, J.S., Kucha, C.T. and Rabiu, I.A. (2015)
Effect of Drying Temperature on
the Nutritional Quality of
Moringa oleifera
Leaves.
African Journal of Food Science
,
9, 395-399. https://doi.org/10.5897/AJFS2014.1145
[18] Anelich, L.E.C.M., Kock, J.L.F., Roux, M.P., Botha, A., Benzuidenhout, S.M., Coet-
zee, D.J. and Venter, P. (2001) The Quality of Used Frying Fats in South Africa.
South African Journal of Science
, 97, 289-290.
[19] Midiwo, J.O., Gikonyo, N.K., Wanjau, O.M., Matasi, J.J. and Waterman, P.G. (1992)
Flavonoids of
Polygonum senegalense
(Meisn) Part II: More Surface and Internal
Tissue Flavonoid Aglycones.
Bulletin of the Chemical Society of Ethiopia
, 6, 19-122.
[20] Ogweno Midiwo, J., Yenesew, A., Juma, B.F., Derese, S., Ayoo, J.A., Aluoch, A.O.
and Guchu, S. (2002) Bioactive Compounds from Some Kenyan Ethnomedicinal
Plants: Myrsinaceae, Polygonaceae and
Psiadia punctulata
.
Phytochemistry Re-
views
,
1, 311-323. https://doi.org/10.1023/A:1026029609500
[21] Paquot, C. and Hautfenne, A. (1987) Standard Methods for the Analysis of Oils,
Fats and Derivatives. Blackwell Scientific Publications, London, 199-211.
[22] Zhang, B.-Y., Wang, H., Luo, X.-D., Du, Z.-Z., Wu, H.-F., Shen, J.-W. and Zhang,
X.-F. (2012) Chemical Constituents of
Euphorbia tangutica
.
Natural Product Re-
search
, 26, 2309-2315. https://doi.org/10.1080/14786419.2012.668686
[23] Mosmann, T. (1983) Rapid Colorimetric Assay for Cellular Growth and Survival:
Application to Proliferation and Cytotoxicity Assays.
Journal of Immunological
Methods
, 65, 55-63. https://www.ncbi.nlm.nih.gov/pubmed/6606682
https://doi.org/10.1016/0022-1759(83)90303-4
[24] Rubinstein, L.V., Shoemaker, R.H., Paull, K.D., Simon, R.M., Tosini, S., Skehan, P.,
Scudiero, D.A., Monks, A. and Boyd, M.R. (1990) Comparison of
In Vitro
Antican-
cer-Drug-Screening Data Generated with a Tetrazolium Assay against a Diverse
Panel of Human Tumor Cell Lines.
Journal of the National Cancer Institute
, 82,
1113-1118.
[25] Jayaprakasam, B., Damu, A.G., Blond, A. and Bodo, B. (1999) Dihydroechioidinin, a
Flavanone from
Andrographis echioides
.
Phytochemistry
,
52, 935-937.
https://doi.org/10.1016/S0031-9422(99)00295-2
[26] Wu, T.-S., Kuoh, C.-S., Ho, S.-T., Yang, M.-S. and Lee, K.-K. (1981) Flavanone and
Other Constituents from
Onychium siliculosum
.
Phytochemistry
, 20, 527-529.
https://doi.org/10.1016/S0031-9422(00)84186-2
[27] Jeong, J.-M., Kang, S.-K., Lee, I.-H., Lee, J.-Y., Jung, H. and Choi, C.-H. (2007) An-
O. M. Wanjau et al.
DOI:
10.4236/fns.2018.911091 1284 Food and Nutrition Sciences
tioxidant and Chemosensitizing Effects of Flavonoids with Hydroxy and/or Me-
thoxy Groups and Structure-Activity Relationship.
Journal of Pharmacy & Pharma-
ceutical Sciences
, 10, 537-546. http://www.cspsCanada.org
https://doi.org/10.18433/J3KW2Z
