Abstract
The polyphenolic composition, oleoresin contents and antioxidant activities of 10 elite accessions of ginger (Zingiber officinale Roscoe) were investigated using standard procedures. The accessions of ginger contained significant quantities of polyphenols and oleoresin which suggested their therapeutic potentials. The antioxidant activities of extracts of the ginger accessions as determined by reducing power tests and their scavenging activities on 2, 2 diphenyl-1-picylhydrazyl radical, indicated that most of them possessed very strong antioxidant activities with higher reductive capacity than standard quercetin at higher concentrations. There was a negative correlation between percentage oleoresin versus phenol (r2=-0.328) but a positive correlation between oleoresin versus percentage inhibition of DPPH radical (r2=0.251) and reducing power (r2=0.494). We obtained a positive correlation between the percentage inhibition of DPPH radical versus phenol (r2=0.827) and reducing power (r2=0.736) suggesting that any of the three assays could be used to determine the antioxidant activity of ginger, but a negative correlation between the percentage inhibition of DPPH radical versus flavonoids (r2=-0.754). Finally, we obtained a negative correlation between flavonoids versus reducing power (r2=-0.926). Results show these accessions of ginger will possess high economic potentials and could be utilized in the treatment of diseases that implicate free radicals. In addition, the oleoresins in ginger could contribute significantly to the reductive capacity of ginger. Finally, the negative correlation we obtained between the percentage inhibition of DPPH radical versus flavonoids and reducing power suggest to us that the flavonoids in ginger may have no contribution to their reductive capacity or hydrogen donating ability.
Highlights
A free radical is an atom or molecule with one or more unpaired electrons
These biological functions of ginger have been attributed to its antioxidant potentials that arise from its contents of oleoresin and essential oils
The significant correlation we obtained between the percentage inhibition of DPPH radical versus phenols and reducing power suggest to us that any of the three assays could be utilized to determine the antioxidant activity of ginger
Summary
A free radical is an atom or molecule with one or more unpaired electrons. Its tendency to acquire electrons from other sources makes it reactive. In disease conditions, the body’s natural antioxidant defensive mechanism is compromised These free radicals can oxidize nucleic acid, proteins, lipids or DNA causing diseases such as: cancer, hypertension, heart attack, diabetes, AIDS and malaria [1,2]. In addition to its food value, ginger has some considerable medicinal values such as: allay of motion sickness, protection of the DNA and other molecules from cell damage induced by oxidation, improvement of sperm quality and reproductive efficiency of men as well as hypoglycemic actions which were reported in animal models [10,11,12] These biological functions of ginger have been attributed to its antioxidant potentials that arise from its contents of oleoresin and essential oils. As a measure of selecting the most elite accessions, further breeding as well as screening studies were carried out and the most promising accessions in terms of oleoresin were selected and analyzed for polyphenolic contents and antioxidant activities and the results are reported in this paper
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