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Title : Antioxidant Polyphenolics : Common factors of prophylaxis in Mauritian plant
based foods and the endemic flora
T. Bahorun1, V.S. Neergheen1, V. Luximon-Ramma1, M.A, Soobrattee1, A. Crozier2 and
O.I.Aruoma3
1
Department of Biosciences, Faculty of Science, University of Mauritius
Plant Products and Human nutrition Group, Graham Kerr Building, Division of Biochemistry
and Molecular Biology, Institute of Biomedical and life Sciences, University of glasgow,
Glosgow G128QQ, UK
3
Department of pharmaceutical and Biomedical Sciences, Touro College of Pharmacy, 230 West
125th Street, New York, NY 10027, USA
2
Abstract :
A large number of studies provide convincing evidence of the beneficial role of plant foods and
their nutraceuticals for the maintenance of health (Kris-Etherton et al, 2002) Epidemiological
studies show a protective effect of fruits, vegetables, plant preparations and beverages like teas
against the risk of development of chronic diseases such as cancer, atherosclerosis, cardiac
dysfunctions, diabetes, hypertension and neurodegenerative disorders (Bazzano et al, 2001 ;
Singh et al, 2002) . The benefits that plant rich diets confer are believed to be ascribed to various
antioxidants, especially carotenoids and antioxidant vitamins including ascorbic acid and
tocopherols. However the antioxidant capacity of a particular plant extract may originate from
compounds other than ß-carotene, vitamin C or vitamin E. The significance of phenolics such as
catechins, phenylcarboxylic acids, phenylpropanoids, anthocyanins and proanthocyanidins as
dietary antioxidants in fruits, vegetables, medicinal plant extracts and teas is being, in this respect
increasingly suggested (Bahorun et al, 2004 ; Vági et al, 2005) . The antimutagenic, antibacterial,
anti-inflammatory, antithrombotic and vasodilatory actions of polyphenolics are well
characterized (Middleton et al, 2000) and accumulating chemical, biochemical, clinical and
epidemiological evidence supports the chemopreventive effects of phenolic antioxidants against
oxidative stress-mediated disorders (Mandel and Youdim, 2004). The pharmacological actions of
phenolic antioxidants are strongly suggested to stem mainly from their free radical scavenging
and metal chelating properties as well as from their effects on cell signaling pathways and on
gene expression (Toyokuni et al 2003, Soobrattee et al, 2005). Mauritius is a tropical island in the
Indian Ocean with a relatively high prevalence of cardiovascular diseases ( 51% of total annual
deaths), cancers ( 11% of total deaths and diabetes ( 20% of the Mauritian population affected).
Dietary nutraceuticals from food and medicinal plants are widely suggested to have prophylactic
effects against reactive oxygen and nitrogen species ( ROS and RNS) mediated pathologies. This
has triggered interest in the role of natural antioxidants as a therapeutic strategy for the
management of diseases in many countries. In this regard, the biopotency and antioxidant
prophylactic properties of Mauritian plant based foods and endemic plant species were
investigated (Mersch-Sundermann et al, 2006 ; Neergheen et al, 2006 ; Bahorun et al, 2007 ;
Soobratee et al, 2008). Furthermore the protective effects of black tea infusates on a number of
markers of oxidative stress indicative of ischaemic heart diseases among the Mauritian population
was assessed in a clinical trial.
17 commonly consumed exotic fruits were analysed for their antioxidant capacity, total phenolics,
proanthocyanidins, flavonoids and vitamin C content. The antioxidant activities of the fruits
ranged from 1 to 47 μmol Trolox equivalent (TEAC) g –1 fresh weight and from 11 to 360μmol
ferric reducing antioxidant power (FRAP) g-1 fresh weight. Total phenolics in the fruits ranged
from 118 to 638 μg g-1 fresh weight, proanthocyanidins from 7 to 2561 μg g-1 fresh weight,
flavonoids from 21 to 712 μg g-1 fresh weight and vitamin C content from 8 to 1426 μg g-1 fresh
weight. There were strong correlations between antioxidant activity (assessed by both TEAC and
FRAP) and total phenolics and proanthocyanidins. Flavonoids seemed to contribute less to the
antioxidant potential of the fruits, while very poor correlations were observed between ascorbate
content and antioxidant activity. The highest antioxidant capacities were observed in red and
yellow Psidium cattleianum Sabine ‘Chinese guava’, sweet and acid Averrhoa carambola L
‘starfruit’, Syzygium cumini L Skeels ‘jamblon’ and white Psidium guajava L ‘guava’. These
fruits were also characterised by high levels of total phenolics.
Antioxidant activities of the 10 vegetables analysed ranged from 0.43 to 3.68 μmol g-1 fresh
weight Trolox equivalent antioxidant capacity (TEAC) and from 0.60 to 8.47 μmol g-1 fresh
weight ferric reducing antioxidant power (FRAP). Levels of total phenols in the vegetables varied
between 132 and 1189 μg g-1 fresh weight and those of total flavonoids between 45 and 944 μg g1
.fresh weight, while proanthocyanidins were detected at very low levels in only a few vegetables.
Vitamin C contents varied between 25 and 748 μg g-1 fresh weight. Quercetin was the dominant
flavonoid aglycone in the hydrolysed vegetable extracts, with values in the range of 15-390 μg g-1
fresh weight. There were strong correlations between antioxidant capacity and total phenols
(TEAC, r = 0.91 ; FRAP, r = 0.83) and total flavonoids (TEAC, r = 0.89 ; FRAP, r = 0.82).
Vitamin C contents showed poor correlation with TEAC values (r = 0.33), while no correlation
was observed with FRAP values. Highest antioxidant capacities were observed in Chinese
cabbage (Brassica chinensis L), onion (Allium cepa L), mugwort (Artemisia vulgaris Cantley) and
broccoli (Brassica oleracea L var botrytis L subvar cymosa).
Mauritian endemic plants from the Celastraceae, Erythroxylaceae, Ebanaceae, Rubiaceae,
Sterculaceae, Myrtaceae family were assessed and correlated to their in vitro antioxidant
propensities. A multi-antioxidant assay approach (8 independant assays) was employed to
evaluate the antioxidant capacity of the plant extracts. The data indicate that Eugenia pollicina, E.
orbiculata, S. commersonii, S. glomeratum, S. mauritianum from the Myrtaceae family and
Diospyros species from the Ebenaceae family had important levels of phenolics and were potent
antioxidants. Levels of total phenol ranged from 1 to 103 mg gallic acid equivalent/g fresh
weight while the flavonoid content was estimated between 1 to 16 mg quercetin equivalent/g
fresh weight. HPLC analyses indicated the presence of significant amounts of catechins and their
derivatives, procyanidin dimers and flavonol aglycones. Since plant-derived natural
phytochemicals have shown great potential in the fight against cancer, this research work has
been geared towards the evaluation of the chemopreventive potential of the Mauritian endemic
plant extracts against human cancer cell lines. Leaf extract of Monimiastrum globosum at low
concentrations (98 and 195 μg FW/ml) protected benzo[a]pyrene- dependent DNA damage in
human hepatoma cells, thus exhibiting anti-genotoxic effects. In the same vein, plant extracts
from the genus Eugenia, Syzygium and Myonima (concentration range of 0.05-4 mg FW/ml)
showed promising anti-proliferative activities against MDAMB 231 and MCF-7 human breast
cancer cell lines. Apoptosis has been proposed as a potential target in chemoprevention and in
this study E. pollicina (concentration of 0.5 mg FW/ml) was shown to induce apoptosis of MCF-7
breast cancer cells.
The in vivo investigation of black tea consumption in a randomised clinical trial revealed that
daily consumption of a Mauritian black tea infusate (9 g daily) had a reducing effect on high
fasting serum levels of glucose (> 140 mg/dl: 20%), cholesterol (> 220 mg/dl: 16 %),
triglycerides (> 200 mg/dl: 56%), LDL/HDL ratio (> 3: 37%), uric acid (> 7 mg/dl: 8.5 %),
creatine kinase MB (> 200 U/L: 33%), C-reactive protein (> 4 μg/L: 77%) and GOT/GPT ratio (>
2: 35%) while blood plasma showed an increase in antioxidant status as evaluated by the FRAP
assay (0.2-0.8 mmol/L: 175%) and TEAC assays (1-2 mmol/L: 32%). The above collective data
clearly indicate that Mauritian fruits, vegetables and black tea represent rich sources of
prophylactic antioxidant nutraceuticals that could used as supplements in a balanced diet within
existing programs in the management of chronic diseases. It can also be envisaged that Mauritian
endemic plant extracts with their high levels of phenolic antioxidants can offer a realistic promise
to reduce the incidence of cancer and other oxidative stress mediated disorders including
cardiovascular disorders and neurological diseases.
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