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This study deals with the exploration of new sources of natural antioxidants as well as
developing effective antioxidants. It is a collaborative project between two universities, i.e.
University of Sindh, Jamshoro, Pakistan and St. Cloud State University, U.S.A.; concerning
with (i) investigation of antioxidant potential of some herbs and spices in Pakistan (ii)
exploring antioxidant activity of flavonoids and their metal complexes after the complexation.
Among the food scientists, natural origin is focus of powerful research for exploitation
of newer sources of antioxidants. In extension of the investigations, in the first phase of the
study, a number of botanical materials have been selected for evaluation of their antioxidant
probability.
Antioxidant potential of different spices and herbs such as Ajwain, Cinnamon,
Coriander, Cumin, Fennel, Fenugreek and Kalonji was investigated. The extracts of herbs and
spices were prepared by electrical shaking and soxhlet extraction methods. A number of
solvents ranging from polar to non- polar were used as extractant. Total phenolic content and
antioxidant potentional by 2, 2-diphenyl-1- picryhydrazyl radical (DPPH·) were used as the
parameters to study the effectiveness of extraction medium, i.e. solvent. Among the extracts of
herbs and spices, ethanolic extract was found to be richer in phenolics and antioxidant activity.
Moreover, total phenolic content, total flavonoid content, reducing power, chelating activity
and DPPH· scavenging activity parameters were used for investigation of their antioxidant
potential. From the results it has been deduced that most of the herbal spice materials
exhibited appreciable antioxidant power as; compared to previously exploited sources of
natural antioxidants. The Kalonji was found to be the richest source of antioxidants among the
herbs and spices analyzed. The order of spices in antioxidant potential is Kalonji> Fenugreek>
Cinnamon> Ajwain> Coriander> Cumin> Fennel.
The flavonoids compose one of the most ubiquitous groups of all plant phenolics and
they are an important class of defense antioxidants. The organoleptic properties and human
health scientific studies have revealed their importance in food for maintaining human health.
Flavonoids reduce the risk of stroke and heart disease, protect against relieve hay fever, age-
related vision disorders, asthma symptoms, sinusitis, alleviate inflammatory skin conditions,
reduce inflammation in joints and muscles, common to rheumatoid arthritis, minimize
menopausal hot flushes, shrink hemorrhoids, reduce varicose veins and battle viral infections.
Transition metal ions participate in the initiation of free radical processes. The
antioxidant action of flavonoids has been considered to be via two possible modes of action,
metal chelation and radical scavenging. Radical scavenging arises by donation of hydrogen
atom from the free hydroxyls on the flavonoids nucleus and other possible antioxidant
mechanism for flavonoids is metal chelation through phenolic OH groups, preventing metal-
mediated generation of free radicals and, accordingly, may shelter the potential biological
target from oxidative stress.
However, in the second phase of study, among the most common dietary and
biologically active flavonoids, Quercetin was selected. In order to study the chelation
mechanisms of flavonoids with metal ions that permit a better understanding of their
complexation and antioxidant properties; it has been decided to synthesize their metal (Mn
Co
2+
, Ni
2+
, Cu
2+
2+
,
and Zn2+ ) complexes. This phase of study also consist on the
characterization and investigation of antioxidant activity and the microbial activity of
flavonoid-metal complexes. The thermal analyses as TGA and DSC. UV–Vis, IR, 1H-NMR
spectroscopic technique were also used to asses relevant interactions of flavonoids and metal
ions, the chelation sites are dependence upon the complex structure on the metal/ligand ratio,
the capacity of flavonoids in binding metal ions, and etc. The outcome largely depends on the
experimental condition and the type of assay employed.
The Job's method (continual variation method) was used to validate the stoichiometric
composition of the chelate for the synthesis of metal flavonoid complexes. The complex
formation reactions of M(II) Resulted in the formation of 2:1 metal:ligand complexes
quercetin respectively. 70+ % yield have been found in the method employed for their
synthesis. UV–vis spectroscopy remained the main tool for structural analysis of flavonoids.
Both of the complexes formation and subsequent electron transfer reactions of M(II) with
these ligands were examined by using UV–vis spectrophotometry. The 1H-NMR results
indicate that the quercetin coordinate with two M(II) ion by replacing two of its protons. The
coordination sites and the binding property of quercetin have also been evaluated by IR
spectroscopy, which shows the shift of bands due to the formation of complex.
The antioxidant and antimicrobial potentional of the complexes were studied and
compared with the activity of free quercetin. The quercetin-M(II) complexes are found more
potent free radical scavenger than the parent quercetin ligands and play a prominent role in
protecting from oxidative stress and microbial organisms. This study demonstrates antioxidant
potential of herbs and spices, and shows that the antioxidant activity of a flavonoid may be
enhanced through chelation with metals. |
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