| Summary: | Oligomeric proanthocyanidins form the basis of neutraceutical anti-oxidant products sold under
trade names such as Pycnognol™ and OPC's. These compounds fall in the class of compounds
called condensed tannins and are essentially the hot water extracts of certain grape seed or pine
species. The oligomeric proanthocyanidin fraction consists mostly of procyanidins, but includes
a propelargonidins and prodelphinidins, as well. These compounds may form separate polymers,
may be combined in a variety of conformations, and may be gallated or glycosylated.
Although these compounds have been found to have many functions in plants, it is the
applications in human medicine that has made them particularly interesting. Oligomeric
proanthocyanidins have been shown to be antioxidant, free radical scavenging, antiinflammatory,
and antihistamine. They have been studied for their prevention of cardiovascular
diseases, tumors, and virus induced conditions, such as HIV. Traditionally, these compounds
have been used by indigenous peoples almost exclusively for gastrointestinal disorders.
Much of the research conducted into the physical properties and biological activity of this class
of compounds has excluded reporting the quantity of the compounds extracted from the various
tree and grape seed sources. This is largely because standardized quantification is not yet
possible. Because proanthocyanidin biosynthetic pathway enzymology is not yet complete, the
nomenclature for these compounds has not been definitively established. Compounds require
identification before meaningful quantification can be made. However, as research in this field is
still ongoing, quantification based on what is already known can be made on the medically active
components of proanthocyanidins.
The butanol-HCl (anthocyanidin), vanillic acid, and protein precipitation methods have been
devised as methods for the quantification of tannins. However, all of these methods have
deficiencies that make them unsuitable for the quantification of proanthocyanidin oligomers with
confidence. The butanol-HCL method quantifies coloured proanthocyanidin hydrolysates relative
to polymer sorghum or quebracho tannin. Different types of proanthocyanidins yield different
colours and different colour intensities, and the colour intensity decreases in strength with the
decreasing size of the oligomer. The vanillin acid method, which quantifies the coloured
proanthocyanidin - vanillin adduct, actually measures the number of phloroglucinol-like A-rings
associated with flavonoids. This reaction is quantified in catechin equivalents, and is sensitive to
reaction time, temperature, light, age of the sample and even the water content in the reaction
mixture, making this method very undesirable for testing various natural extracts. The protein
precipitation method is unable to distinguish between condensed and hydrolyzable tannins.
The method described herein is designed to quantify oligomeric proanthocyanidins by
determining the occurrence of 10 signature procyanidins [OPC], identifying seven of the ten
signature procyanins, and cumulatively measuring the concentration of the 10 signature peaks
relative to a commercial oligomeric proanthocyanidin product, Indena brand LeucoSelect™.
Because the quantification is made relative to an already commercialized product, the
quantification results predict the amount of salable product in natural product extract. This
method is reproducible, rapid, efficient, and can be used to screen for potential new sources of
OPC-based products, or to compare the oligomeric proanthocyanidin content in various
commercial products. When used to quantify the OPC content in bark extracts, this method was
found to provide results similar to those in the literature.
By using this method and screening various bark extracts, it was found that sample freshness
played a role in the extractable amounts of proanthocyanidins. In future studies, fresh samples
should be used as they most accurately represent the bark composition on live trees. The inner
and outer bark quantities of proanthocyanidins were also seen to vary, with the inner bark
quantity almost always being greater in concentration than that in the outer bark. Douglas-fir and
interior Amabilis fir were found to be the best sources of oligomeric proanthocyanidins at 43.2
and 12.4 mg/g dry inner bark, respectively. The samples of lower mainland Amabilis fir, interior
Lodgepole pine, and Caribbean pine from Venezuela, all showed signs of being potential sources
of OPC products. Interior and lower mainland Sitka spruce and interior Western hemlock showed
little potential as possible sources of OPC's.
By comparing the commercially produced OPC containing products relative to the Indena brand
LeucoSelect™ (made from grape seeds) the Capers brand grape seed extract was shown to be
77% similar to the Indena standard. Nu-Greens Prolong, which differed substantially, was shown
to be only 7.2% similar to the Indena standard, raising questions about its quantification in units
of 'Activity'. The SunForce Pycnogenol™ was found to be only 46.8 % similar, but is sourced
from pine bark, which would seem to have a higher concentration of higher molecular weight
OPC's, not included in the 10 signature peaks.
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