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Grape Seed Extract White Paper Prepared by: The Grape Seed Method Evaluation Committee 1. Grape Seed Extracts: Seed Management and Processing Proanthocyanidins are a class of biologically active flavonoids found throughout the plant kingdom, and are one of the most potent antioxidants in nature. Typically concentrated in the bark of trees and in the outer shells of seeds, proanthocyanidins serve to protect plants against oxidative elements such as oxygen and sunshine. In fact, a growing body of scientific evidence suggests that proanthocyanidins are far more powerful antioxidants than vitamins C, E or beta-carotene. One of the richest sources of proanthocyanidins in nature are grape seeds. Recent studies in animals, as well as some human studies, have shown that grape seed proanthocyanidin extracts possess a broad spectrum of biological, pharmacological and chemoprotective properties against free radicals and oxidative stress. Some grape seed extracts have been reported to promote collagen formation, enhance cardiovascular health, improve microcirculation, prevent many of the effects related to premature aging, inhibit growth and formation of certain types of cancer, and protect cells against drug, chemical and environmental pollutants toxicity. However, a wide degree of variability exists between the composition and biological make up of the various grape seed extracts on the market. A Complex Product Proanthocyanidins come in a multitude of chemical structures and sizes consisting of base units called "monomers." Proanthocyanidins containing two or more monomers chemically linked together are called oligomeric proanthocyanidins or "OPCs." OPCs containing two monomers are called dimers, three monomers are called trimers, four are called tetramers, five pentamers, etc. To illustrate the complexity of the compounds that exist in grape seed extracts, consider this: There are basically two proanthocyanidin monomers called "catechin" and "epicatechin." Each of these bind at either the alpha or beta position on their molecular structures to form dimers, trimers, etc. In addition, catechin and epicatechin can also form numerous esters from gallic acid, called catechin or epicatechin "gallate", as well as various sugar and protein molecules called "glycosides" and "peptides", respectively. In fact, the total number of possible dimers, including gallic acid and glucose esters alone, are 162. And each time you add an additional monomer, the total number of possible combinations increases geometrically; trimers jump to over 550, tetramers over 1,200, etc. The result is, unlike a single nutrient compound such as vitamin C (ascorbic acid) or vitamin E (d-alpha tocopherol), OPCs are much more complex and difficult to identify and quantify. Illustrations of Proanthocyanidin Molecules Challenges of Defining OPCs The complexity of OPCs, as well as the diverging interests of many of the companies who sell grape seed extracts, underscores the difficulty the Grape Seed Extract Committee has had in defining OPCs. Quite literally, OPCs consist of two or more proanthocyanidin monomers. However, this definition would include long chains of monomers called polymers and condensed tannins. Some parties believe that polymers and tannins should not be considered OPCs. Others feel differently. In addition, there is general disagreement in defining what a polymer is. Five or more monomers? Seven or more? Ten or more? Although there is evidence to suggest that smaller OPCs, such as dimers, trimers and tetramers, are more soluble and bioavailable than larger OPCs, there is also evidence to suggest that less soluble polymers and tannins are beneficial as well. Recently, Hagerman, et al., have shown that polymeric proanthocyanidins and tannins are 15 to 30 times more effective at quenching free radicals than are simple polyphenols. Since polymers and tannins are not well absorbed, the researchers suggest that they could exert their antioxidant activity within the digestive tract to protect lipids, proteins and carbohydrates from oxidative damage during digestion, and spare absorbable antioxidants such as vitamins E, C and beta-carotene. What About Monomers? Grape seed extracts also contain monomers. Depending upon the extraction process, the monomer content of grape seed extracts can range from less than one percent to as high as 30 percent. There is debate among the various suppliers of grape seed extracts over the value of grape seed monomers. However, studies show that OPCs confer properties that monomers don’t, such as collagen formation. Furthermore, grape seed extracts are poor sources of monomers compared to green tea extracts, which contain significantly higher levels of more beneficial monomers, such epigallocatechin gallate (EGCG), at a much lower cost, than do grape seed extracts. Green tea extracts, on the other hand, are not the best sources of OPCs. In addition, grape seed extracts may consist of hundreds of known, and perhaps thousands of unknown, naturally occurring, biologically active substances that aren’t OPCs, such as quercetin, ferulic acid, caffeic acid, coumaric acid and myricetin. These compounds are typically found in the skin, pulp, stem and leaves of the plant. Their presence in a grape seed extract indicates that the seeds had probably undergone fermentation which causes these compounds to adhere to the surface of the seed during the process and that stems and seeds were present during extraction. The amount and types of compounds present in a particular grape seed extract can vary and is greatly influenced by the extraction process, as well as the source, variety and storage of seeds used. Seed Management The grape seeds used in the manufacture of commercially available grape seed extracts are typically derived from varietal wine grapes (Vitis vinifera). These grapes can have over 12 times the level of polyphenols found in the Thomson, Flame and Black seedless varieties. Typically, naturally occurring wine grape seeds contain 50-1000mg/kg (less than 1 percent) monomers, 120-1400mg/kg oligomers and 1250-1700mg/kg higher molecular weight polymers or tannins. In contrast, grape skins contain 14-66mg/kg monomers, 35-200mg/kg oligomers and 20-750mg/kg polymers., The source and variety of wine grape seeds used in the manufacture of grape seed extracts can affect the composition of the extract. Bourzeix et al. compared the proanthocyanidin composition of different varietal grape seeds and found that the amount of catechin and epicatechin monomers ranged from 51mg/kg in Carignan grape seeds to 1100mg/kg in Pinot Noir grape seeds, with Cabernet Sauvignon having 285mg/kg.24 Oligomeric proanthocyanidins ranged from 114mg/kg in Carignan to 1275mg/kg in Pinot Noir, while Cabernet Sauvignon had 371mg/kg. Polymers ranged from 6-73 percent. Both red and white grape seeds are used in the manufacture of commercial grape seed extracts. Generally, red grape seeds have a higher total polyphenolic content than white grape seeds; 3500mg/kg on average for reds compared to 2800mg/kg on average for whites. Seeds used in the manufacture of grape seed extracts can be acquired from either grape juice operations or from wine producers after they have been discarded from the winemaking process. Red grape seeds obtained from a winemaking facility accompany the grape juice and skins during the fermentation process and typically lose about 30-50 percent of their polyphenolic content.25 In fact, it is the polyphenolic content of red wine (extracted from the seeds) that gives it its astringent or "puckery" quality. White grape seeds, on the other hand, are removed from the juice prior to fermentation and, thus, retain a significantly greater portion of their polyphenols. Another factor that affects the polyphenolic content of the seeds is the actual wine making process called "vinification." Most wines are made by conventional procedures, but some wine styles such as "Nouveau" rely on carbonic maceration. Thermovinification is utilized in areas where red wine is made from grapes that are poor in color, for instance, in cooler areas where it is difficult to obtain fully ripe red grapes. On average, conventional vinification removes about 30 percent more polyphenols from the seeds than do thermovinification or carbonic maceration.25 The most important aspect of seed management, however, is the drying, separation and storage, which can have a dramatic effect upon the potency and viability of the seeds as well as the extracted product. Ideally, seeds used to manufacture grape seed extracts would be processed right away; that is, separated from the macerated skin and immediately subjected to the extraction process. But as a practical matter, this is not possible. For starters, wine grapes are a seasonal agricultural crop. Thus, vast amounts of macerated seed and skins (called "pomace") must be acquired in a short period of time. This period, called the wine "crush", typically runs from August to November in the Northern hemisphere and from February to April in the Southern hemisphere. Grape pomace has a high moisture content and is highly perishable. Thus, the seeds need to be extracted or separated from the skin and preserved as soon as possible. Several methods of drying are commonly used, including sun drying or mechanical drying using ovens or kilns. Another method of preserving seeds is to separate them from the skins wet then freeze them. Importantly, the seeds must be stored properly to prevent mildew or oxidation. Improperly stored seeds have been known to rapidly lose their potency and render them useless for extraction purposes. As an interesting side note, OPCs are present in the outer shell of grape seeds, put there by Mother Nature to protect the seed and help propagate the species. After falling from the vine, OPCs serve as the grape seed’s first line of defense against oxidizing elements such as sun (UV rays) and air (oxygen), which can destroy seed cell membranes and damage DNA the same way they cause cellular damage in people. However, in the process of conferring their protection, the OPCs become oxidized themselves. By removing excess moisture and minimizing their exposure to oxidizing elements, grape seeds can be stored for prolonged periods of time, while maintaining their OPC potency. Seed Processing The primary distinction between the various grape seed extracts available on the market today is their manufacturing or extraction process. Significant differences exits in the manufacture of the various grape seed extracts available. Each of these processes possess their own unique set of advantages and disadvantages, which can affect composition, potency, manufacturing yield, cost, etc. Although details of these processes are the subject of proprietary information, there are two basic approaches: 1) solvent extraction and 2) water and ethanol extraction. Solvent extraction uses one or more organic solvents such as acetone, methylene chloride or toluene to remove and separate the OPCs from the grape seeds. The solvents are then recovered and the resulting concentrate is then either spray dried or vacuum dried and ground to final specifications. Similar manufacturing procedures are employed in some water and ethanol processes, while others involve complex filtration, concentration and purification steps. Although water and ethanol may be used in a "solvent extraction" process, the term "water and ethanol extraction" should be reserved for processes that use only water and ethanol, and do not use any other organic solvent. But Does It Work? While considerable time and effort have been spent on the composition and analysis of grape seed extracts, the real question is, do they work? Current methods of analysis such as GAE, HPLC and GPC are potentially useful for monitoring production batch consistency, determining product composition and quantifying ingredient label claims, but none of these analyses actually tell you if the product works. They don't tell you if it’s bioavailable, biologically active, efficacious or even safe. Research shows that many of the components of grape seed extracts, such as OPCs, are biologically active and efficacious. However, grape seed extracts contain more than just OPCs. They contain hundreds of known, as well as many unknown, naturally occurring substances, many of which may possess biological benefits yet to be discovered. Unfortunately, a wide degree of variability exists between the composition and biological make up of the various grape seed extracts available. The best way to sort through these differences is to compare the research available on each product. Research on a given grape seed extract can be obtained by contacting the source manufacturer. Since many grape seed extract manufacturers are currently using the research done on other products to support the efficacy of their own, it is important to ask for research done specifically on the grape seed extract you are inquiring about. Since grape seed extracts vary widely in their chemical composition, there are no guarantees that one product works the same as another. 2. Methods of Analysis Grape seed extract is a heterogeneous mixture of gallic acid, monomers, dimers, trimers, tetramers, polymers and other oligomers. The basic building blocks are molecules of catechin, epicatechin, epicatechin gallate, gallic acid esters, glycosides and peptides. Due to the high degree of heterogeneity, several analytical techniques are required to characterize grape seed extract. TLC (Thin Layer Chromatography)
lack of a non-partisan "commercial" grape seed extract standard
This procedure was proffered by ESA Laboratories and includes normal phase TLC separation of preacetylated powder extracts In 1998 three independent laboratories (Alpha Chemical Laboratory, Industrial Laboratory, and PhytoChem) validated the TLC method by testing 14 grape seed extracts, bilberry, green tea, pycnogenol and cranberry extracts as well as 13 finished products. This is a qualitative test designed to identify grape seed extract and differentiate it from botanicals that may have similar components. Procyanidolic Value and Porter Value The Procyanidolic assay is also referred to as the Bate-Smith assay.
The "Procyanidolic Index" (also called the Bates-Smith Assay) involves a testing method that measures the change in color when the product is mixed with certain chemicals; the greater the color in change, the higher the OPCs. It must be noted, however, that the Procyanidolic Index is a relative value that can measure well over 100. Unfortunately, a Procyanidolic Index of 95 was erroneously taken to mean 95% OPC by some and began appearing on the labels of finished products. . All current methods of analysis suggest that the actual OPC content of these products is much lower than 95%. The Porter and Procyanidolic value assays are colorimetric tests based on acid hydrolysis. Dimer and larger molecules are converted to anthocyanidins by acid hydrolysis. A standard curve is not incorporated and thus results can only be reported as values, not as percentages. Another artifact of these two assays is that on a molar basis the values increase with molecular size, i.e. if a grape seed extract is comprised primarily of larger polymers, it will have higher Procyanidolic and Porter values than an extract comprised of the same molar concentration of dimers. It is also difficult to obtain reproducible results with the Procyanidolic value assay, as the results are very dependent on the testing conditions and cyanidin (the anthocyanidin formed during the acid hydrolysis step) is relatively unstable. Dr. V.L. Singleton, a world-renowned authority on grape phenols commented on the Procyanidolic assay "values obtained are necessarily somewhat arbitrary". Three independent laboratories conducted a study on both the Porter and Procyanidolic value assays in early 1997 (Industrial Laboratories, Alpha Chemical and Biomedical Laboratories and Hauser) and found large lab-to-lab variation in the Procyanidolic assay. Some companies utilize a modified Bate-Smith assay to increase the reproducibility of results. The Porter assay contains ammonium iron (III) sulfate, which stabilizes the reaction better than in the Procyanidolic assay and renders the results less dependent on conditions. Procyanidolic assay proanthocyanidins (dimers & larger) + HCl/isopropanol + heat = cyanidin, Abs 550 nm Porter assay proanthocyanidins (dimers & larger) + NH4Fe(SO4)2 · 12 H2O + HCl/n-butanol + heat = cyanidin, Abs 550 nm
The chemical reaction to the right depicts both the Porter value and Procyanidolic Value assays.
Total phenols (Folin-Ciocalteau) Total phenols (Folin-Ciocalteau)
This is a colorimetric oxidation/reduction assay that measures all phenolic molecules with no differentiation between gallic acid, monomers, dimers and larger phenolic compounds. A gallic acid standard curve is used and results are typically expressed as gallic acid equivalents (GAE). This method has been used in the wine industry for over 30 years. The first paper on this method was published in 1927 and in 1965 Singleton and Rossi improved the reproducibility of the assay. Swain and Goldstein considered this the method of choice for estimating total phenol content in complex plant products. This is a sensitive and quantitative method, independent of the degree of polymerization.
phenolics + alkaline + FC reagent + heat = blue colored product, Abs 755 nm FC reagent is an oxidizing agent comprised of heteropolyphosphotungstate-molybdate. The blue colored product is a mixture of the 1-, 2-, 4-, and 6-electron reduction products in the tungstate series P2W18O62-7 to H4P2W18O62-8 and the 2-, 4-, and 6-electron reduction products in the molybdate series H2P2Mo18O62-6 to H6P2Mo18O62-6. Some work has been initiated to determine if monomers react differently than larger molecules in this assay. Preliminary results show that the standard F-C assay may be biased in favor of grape seed extracts with high monomer contents since monomers and OPCs in grape seed extracts have different response factors. (See Addendum A: Calculation of Monomer Bias Correction Factor.) Label claims based on these results will be relative to the response factor of the compounds being tested. There is no study that we are presently aware of that has made a definitive 1:1 correlation between the mass of OPCs (monomers, oligomers or polymers) and an equal quantity of gallic acid. The method can be used for standardization, but not direct quantitation. Work is continuing in this area. This method has been cited as being the Association of Official Agricultural Chemists’ method for determining total polyphenol content in wines. Vanillin assay, with methanol as the solvent
with glacial acetic acid as the solvent
The vanillin assay has been utilized in the cereal industry since the 1950’s. Dr. Larry Butler (Purdue University) has done many comparative studies with sorghum. The kinetics of the reaction are different with the two solvents (methanol and glacial acetic acid), with methanol yielding the more complicated kinetics. With glacial acetic acid the reaction kinetics are less complex (i.e. monomers and polymers react similarly), the reaction only occurs at the end groups, and the colored product which is formed and measured is more stable. Obtaining reproducible results with the vanillin assay with methanol may be difficult. The person running the analysis must be well-trained and the results are dependent on such techniques as the angle the methanol is added to the vial. The article by Butler et. al contains the statement "for convenience, catechin, a monomeric flavan-3-ol unit of condensed tannins, is often used to standardize the assay rather than purified condensed tannin, although this leads to a considerable overestimation of tannin content". Further in the article it is also stated that "methanol affects the reaction with flavan-3-ol monomers and their oligomeric and polymers quite differently, producing complex kinetic patterns that make standardization of tannin analysis with monomers such as catechin tenuous at best." Reverse Phase HPLC (High Pressure Liquid Chromatography) With this method the percent by weight of gallic acid and phenolic monomers such as
catechin, epicatechin and epicatechin gallate can be determined by using readily available
standards from such companies as Sigma/Aldrich. Unfortunately, except for one dimer, no
large molecule phenolics are commercially available. In past experiences grape seed manufacturers have found that there is no standard
RP-HPLC procedure among independent laboratories and that a simple request for % monomers
will yield different results as well as different compounds. If this analysis is to be
performed by an independent laboratory the monomers of interest (i.e. those typically
found in grape seed extract) must be stated: catechin, epicatechin, and epicatechin
gallate, as well as gallic acid (a phenolic acid). Depending on the solvents used and the
length of the run some of the monomer peaks may co-elute with other phenolics. Care needs
to be given to ensure that peaks of interest are pure peaks (i.e. no co-elution) and that
the larger phenolic molecules are flushed from the column prior to subsequent runs.
GPC (Gel Permeation Chromatography) epicatechin but these two monomers have different absorptions at 280nm. not everyone has the necessary instrumentation use of a non-partisan standard difficult to differentiate types of phenol present (e.g. monomer vs. dimer vs. trimer) some have noted that larger molecules seem to "stick on the column" The basic principle of gel permeation chromatography is that molecules are separated by
size on a specific column and when they elute the intensity of absorbency is measured at a
specific wavelength, 280nm for phenols. All of the molecules tend to elute in a hump and
the peak area of the hump is directly proportional to the concentration of phenols in the
product, relative to the "reference material". An internal standard is used to
improve the accuracy of the results. Fuzzati et. al. identified three separate regions of
the "hump" as 1) monomers, 2) monomers, dimers and their gallates and 3) trimers
through heptemers and their gallates based on a "well characterized reference
material" and mass spectroscopy. 3. Labeling Guide
When the committee first met over three years ago the predominant marketing claim was the OPC or oligomeric proanthocyanidin content. Unfortunately, the lack of definitions and accurate, meaningful testing methods led to confusion in the marketplace; not just to the consumer but also to the manufacturer seeking to provide the best and most efficacious product. Today, a survey of the labels available for grape seed extract proved to be somewhat less confusing; the addition of the Supplement Facts Chart/Ingredient List has done much to bring some clarity to the category. The goal of this document is to educate the reader and creator of grape seed labels to further the understanding and continuity.
Definitions Below is a list of terms that can and should appear on the Supplement Facts Chart/Ingredient List of grape seed extract. Confusion starts from several terms that are basically synonyms being used sometimes interchangeably and sometimes with the implication they are different. For clarity the synonyms, all of which yield cyanidins upon heating in an acid media from which the term procyanidin originates, are listed here.
Synonyms: Procyanidins Proanthocyanidins Procyanidolic oligomers OPC PCO Leucoanthocyanins Condensed tannins pycnogenols (lower case only) Other terms not defined here are often used in the labeling of grape seed products but are varied and can be considered marketing terms, not definitions.
Proanthocyanidins: Subset of the polyphenols; consisting of the polymers of flavan-3-ols (+)-catechin, (-)-epicatechin, and (-)-epicatechin 3-O-gallate linked by C4-C8 or C4-C6 bonds. Some carry galloyl residues linked to the C-3 alcoholic function of the flavan-3-ol units., pycnogenol: Term for proanthocyanidins used in much of the original research (should not be confused with the Trademarked name Pycnogenol® which is composed of the same types of compounds derived from Pine Bark). Polyphenols: Term that is more general than proanthocyanidins can be used when referring to the results of analytical work done to quantify the total oligomeric, monomeric and galloylated (having attached gallic acid units) components of grape seed extract. The grape seed committee has agreed on some new terms that would give some clarity to the testing methods used to determine the total polyphenol content without adding too many unfamiliar terms or take up valuable label space. (For description of methods see Methods Section).
Polyphenols (GAE): Polyphenols quantified by the Folin-ciocalteau spectrophotometric method and calculated as gallic acid equivalents.
Polyphenols (VAN): Polyphenols quantified by the Vanillin method.
Polyphenols (GPC): Polyphenols quantified by Gel Permeation Chromatography.
Monomers (Monomeric): The sub-units of the procyanidin polymers.
Oligomers (Oligomeric): Condensation products of the monomers as described in the procyanidin definition. Use of Defined Terms in Labeling Taking these definitions into account we can propose some acceptable labeling statements Typically, a label has two distinct parts that describe the grape seed product; the Supplement Facts Box and Ingredient List that is regulated by DSHEA, and the Description Section dedicated to the marketing of the contents.
Supplement Facts/Ingredient List Example A) Dietary Ingredients: grape seed extract 40mg This is the simplest way of accurately declaring the contents.
Example B) Dietary Ingredients: 80mg of grape seed extract (95 percent Proanthocyanidins)
This labeling attempts to provide more information about the grape seed extract, namely the percent of proanthocyanidins contained within the extract. However, the problem here is that there are no analytical methods for determining the proanthocyanidin content. It would be more accurate to list using terms for which a testing method exists, i.e. polyphenols. As grape seed extracts vary greatly in concentration it provides valuable information to include the percent of polyphenols. Sometimes this information is provided in the Description, if not then it is not necessary to also place it in the Ingredient Panel.
Example C) Dietary Ingredients: 80mg of grape seed extract (95 percent OPC’s) In this case we can see that the label attempts the same effect as the one above but again uses a term, OPC, for which there exists no currently validated analytical method. We propose the following as a solution to problems raised in Examples B & C:
Dietary Ingredients: 80mg of grape seed extract (95 percent Polyphenols (GPC, GAE or VAN)) If the manufacturer wishes to describe the relationship between polyphenols and proanthocyanidins, the description panel would provide this opportunity. Example D) Dietary Ingredients:
polyphenols 15mg The Description Panel of this grape seed product describes it as standardized to 50% polyphenols. The Supplement Facts Box as listed above claims 30mg grape seed extract AND 15mg polyphenols. Such listing is confusing, as the product does not contain both ingredients. One solution for this problem might be:
Grape seed extract 30mg (standardized to 50%, polyphenols (GPC, GAE or VAN)) or Grape seed extract 30 mg containing 15 mg polyphenols (GPC, GAE, or VAN) Example E) A Grape Seed complex declares in the: Supplement Facts Box
Dietary Ingredients grapeseed l00mg proanthocyanidins 90mg grape skin and stem 19mg polyphenols 14mg Among other ingredients. The complex contains many plant extracts that can contain proanthocyanidins but this labeling does not make it clear if the proanthocyanidins are from the 100mg of grape seed or from another plant source. The same can be said of the polyphenol content. Polyphenols as we see from the above definition are a very general class or compounds that can be derived from several plant sources. Again, it is not clear here if there are in addition of the grape seed, the grape skin and stem or some other source. One solution for this problem might be:
Grape seed extract 100mg Containing 90mg polyphenols (GPC, GAE or VAN) Grape skin and stem 19mg Containing 14mg polyphenols (GPC, GAE or VAN)
Example F) Dietary Ingredients:
Other polyphenols 14mg catechins and epicatechins 21mg total phenols as gallic acid equivalents 55mg grape seed extract 100mg. Here, we can guess that the components of the grape seed extract are broken down as individual components. This fact is obscured by the addition of the whole extract to the panel. All of these components can be derived from the grape seed. Therefore, it is hard to know from this label if the polyphenols, monomers (catechins and epicatechins) and other phenols (tested with reference to gallic acid) are from the grape seed or in addition to it. Also confusing is the listing of total phenols as gallic acid equivalents without identifying the testing methodology of the other polyphenols and monomeric constituents. One solution for this problem might be [indentation is accepted by FDA]:
Dietary Ingredients Grape Seed Extract 100mg containing 21mg monomers, catechin and epicatechin (HPLC)
Description Panel The Description portion of the labeling is where most manufacturers choose to differentiate their product. Again, using examples, we can analyze the way the terms can be used effectively.
Fair and Accurate:
Note: In this example the testing method for polyphenols is not listed, if it is not listed in the Supplement Facts, then it should be noted here.
Again, the testing method for polyphenols is not listed, if it is not listed in the Supplement Facts then it should be noted here.
Problematic:
This statement implies that the oligomeric proanthocyanidins have been quantified when there is currently no validated analytical method for the oligomeric proanthocyanidins.
This statement again implies that the proanthocyanidins are measured as OPC, which is not precise and then attempts to qualify it by proclaiming the OPC consists of monomers and oligomers.
It is not accurate to claim 95% antioxidants (rather than polyphenols) in the marketing portion of the label when there are currently no defined methods that can accurately delineate what percent is due to the oligomers versus other principles.
The term PAC is novel but does not represent novel compounds. PAC is not a specific set of compounds separate from the proanthocyanidins. No validated analytical method currently exists to quantify specifically the PAC content as opposed to the general polyphenol content.
Addendum A Calculation of Monomer Bias Correction Factor The monomer bias correction factor would be determined in the following way. All calculations would be made on a dry weight basis.
It has been suggested that not all monomers originally proposed for analysis are important in GSE samples. This is correct, there are only certain monomers naturally found in grape seeds and therefore their extracts. However, one of the problems our industry will face is the adulteration of GSEs with green tea or tea extracts to raise the monomer content (and therefore the Total Phenolics). Application of this correction factor will accomplish two things:
If it is decided that it is not necessary or desirable to correct for all monomers present in a pure (unadulterated) GSE sample, then we can determine and correct for only those monomers that significantly inflate the Total Polyphenolics content of a GSE. These monomers can be determined in the following way:
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