الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
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Abstract
Dietary supplements containing Ginkgo biloba L. are of the top best-selling
botanicals in the world. They are used in the treatment of Alzheimer‘s disease,
neurodegenerative disease, cerebral insufficiency, and eye ailments. The major
contributors to the positive biological effects attributed to Ginkgo are flavonol glycosides
and terpene trilactones. The flavonol glycosides are mainly derivatives of quercetin,
kaempferol, and isorhamnetin aglycones. The aglycones themselves occur only in
relatively low concentration in extracts. Approximately 35 flavonoids have been isolated
from Ginkgo biloba L.. Five coumaroyl esters of Ginkgo flavonoids have been isolated and
identified. Coumaroyl esters of Ginkgo flavonol glycosides are unstable because of the
presence of two centres of instability. Accordingly, stability indicating method of assay for
flavonol glycosides is essential. Ginkgolic acids are negative markers found in Ginkgo
biloba L. leaves and extracts.
Monographs for Ginkgo extract can be found in various pharmacopoeias, including
the USP, Ph. Eur., and the BP. The USP monograph for Ginkgo extract specifies a
flavonoid content of 22-27%, calculated as flavonol glycosides, terpene trilactones content
of 5.4-12% consisting of bilobalide ,ginkgolide A, ginkgolide B, and ginkgolide C, and a
maximum content of 5 ppm for ginkgolic acids. As a parameter for quality/authenticity the
USP method also mandates to monitor a quercetin/kaemferol/isorhamnetin ratio of the
hydrolysed extract based on their respective peak areas. The kaempferol peak must be 0.8-
1.2 times the size of the quercetin peak, and the peak for isorhamnetin must be not less
than 0.1 times the size of quercetin peak.
The current USP method for the assay of flavonol glycosides content, in Ginkgo
biloba L. extract, is non-stability indicating. It involves acid hydrolysis of flavonol
glycosides to aglycones and back calculates the total flavonol glycoside content from the
aglycone concentration in extracts. This means that the prescribed assays quantify flavonol
aglycones and not the flavonol glycosides. The latter are responsible for the claimed
activity. Accordingly the pharmacopoeial methods are not capable of detecting adulteration
of Ginkgo extract with free flavonol aglycones. Although the
quercetin/kaemferol/isorhamnetin ratio can detect inferior quality products containing
Ginkgo biloba L. extracts; however it might fail to detect counterfeiting with aglycones.
Terpene trilactones are unique components of Ginkgo biloba L. and they are expensive to
purchase. Accordingly, literature survey does not document counterfeiting with these
compounds. However, the defect in the USP method for the assay of terpene lactones is the
use of refractive index detector with questionable sensitivity.