Antioxidant activity of selected wild orchids of Nepal
Date
2015
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Abstract
The inhibitory or delaying action of both the synthetic chemicals and naturally occurring
phytochemicals against oxidative damage to tissues by free radicals produced in
biological system of living organisms is known as antioxidant activity. Since some
phytochemicals are responsible for biological as well as medicinal activities, nine wild
orchids of Nepal were assessed for total polyphenolics and flavonoids content along with
the antioxidant activity. The ethanolic extract of Eria graminifolia pseudobulbs,
Gastrochilus acutifolius leaf and root, G. distichus whole plant, Luisia trichorhiza leaf
and root, Otochilus albus pseudobulbs, Papillionanthe uniflora whole plant, Pholidota
articulata leaf and pseudobulbs, Rhynchostylis retusa leaf, and Trudelia cristata leaf and
stem were prepared by Soxhlet extraction. Phytochemicals were detected by previously
established protocols with minor modifications. The total flavonoids were estimated with
aluminium chloride method and total polyphenolics content with Folin-Ciocalteu phenol
reagent method. Antioxidant activity was assessed by DPPH (2, 2-diphenyl-1-picryl
hydrazyl) free radical scavenging assay. There was significant variation of total
flavonoids, total polyphenolics content and antioxidant activity among the orchid extracts
at P = 0.05. The total flavonoids varied with highest in Rhynchostylis retusa leaf (110.68
± 4.52 mg QE/g) and lowest content in Gastrochilus acutifolius root (22.32 ± 1.10 mg
QE/g); total polyphenolics with highest in Trudelia cristata stem (69.68±2.78 mg GAE/g)
and lowest content in Gastrochilus acutifolius leaves (11.89±0.64 mg GAE/g). Also, the
antioxidant activity varied with highest in Trudelia cristata stem (IC
79.69 µg/ml) and
lowest DPPH radical scavenging activity in Gastrochilus acutifolius leaf (IC
50
µg/ml). However, none of the orchid extracts were as effective as quercetin – the
reference compound – in radical scavenging activity (IC
32.90 µg/ml). Total
polyphenolics and flavonoids content and antioxidant activity of selected orchid extracts
in this study were higher or lower than medicinal plant and orchid extracts of previous
studies with considerable margin. Again, their antioxidant activity was positively
associated with total flavonoids and total polyphenolics content. Hence, this study claims
that the ethanol extract of selected wild orchids perform significantly varying antioxidant
activity with further possibilities of pharmacognistical and pharmacological studies.
Description
Keywords
Antioxidant activity, Phytochemical