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The Lipid Research Laboratory, Technion Faculty of Medicine, The Rappaport Family Institute for Research in the Medical Sciences and Rambam Medical Center, Haifa, Israel
* To whom correspondence should be addressed. E-mail: fuhrman{at}tx.technion.ac.il.
Dear Editor,
In our article, Grape powder polyphenols attenuate atherosclerosis development in apolipoprotein E deficient (E0) mice and reduce macrophage atherogenicity, we investigated the effects of a standardized freeze-dried preparation, made from fresh grapes, on the susceptibility of LDL to oxidative modification, on the atherogenicity of macrophages, and on the atherosclerotic lesion development in the atherosclerotic apolipoprotein E–deficient mice(1). The freeze-dried grape powder contains 90% sugar (about half of it is glucose and half is fructose) and 5.8 mg of total polyphenols/g powder. Flavanols are the major flavonoids in the grape powder (4.1 mg/g powder, Table 1), followed by anthocyanins (0.77 mg/g powder), flavonols (40.6 µg/g powder), and stilbenes (resveratrol, 1.66 µg/g powder). In our study, the grape powder was dissolved in water at a concentration of 10 g of powder/L. In order to increase the yield of polyphenols in the water extract, we stirred the water solutions of grape powder for a period of 5 h at room temperature. Because the preparation formed a slurry suspension, it was centrifuged to remove the insoluble materials. The supernatant was then assayed for its total polyphenols content. As much as 90% of total polyphenols in the grape powder were recovered in the water extract, as demonstrated by 5.2 mg polyphenols/g of powder measured in the water extract. These results suggest that most of the polyphenols present in the grape powder were recovered in the water extract, and that their composition is similar to the polyphenol composition in the grape powder. The solubility of polyphenols in water is determined by their polarity. Flavanols, such as catechin or epicatechin, known to be present in grapes (2), are polar compounds, and therefore are soluble in water (3). Flavonols, which are insoluble in water, are usually found in foods in their glycosylated form (4). Thus, the flavonols present in grapes are probably present in the glycosylated form, particularly in view of the high concentration of glucose in the grape dry powder, and the glycosylation of the polyphenols increases their solubility in water. The same is true for the stilben resveratrol, as has been demonstrated previously (5). In addition, the anthocyanins, which are glycosides of anthocyanidin, are also water soluble. Taken altogether, these can explain the high recovery of the polyphenols from the grape powder in the water extract administered to the mice in our study. The antiatherogenic effects observed after consumption of the grape powder water extract can therefore be attributed to the antiatherogenicity of the grape polyphenols. However, in agreement with Dr. Chow's comment, these results do not exclude the possibility that other water soluble compounds found in the grape extract possess antioxidant properties, and could contribute to the inhibitory effect on atherosclerosis development.
Manuscript received 15 May 2006.
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LITERATURE CITED |
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 TOP LITERATURE CITED |
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1. Fuhrman B, Volkova N, Coleman R, Aviram M. Grape powder polyphenols attenuate atherosclerosis development in apolipoprotein E deficient (E0) mice and reduce macrophage atherogenicity. J Nutr. 2005;135:722–8.
2. Lekakis J, Rallidis LS, Andreadou I, Vamvakou G, Kazantzoglou G, Magiatis P, Skaltsounis AL, Kremastinos DT. Polyphenolic compounds from red grapes acutely improve endothelial function in patients with coronary heart disease. Eur J Cardiovasc Prev Rehabil. 2005;12:596–600.[Medline]
3. Chafer A, Pascual-Marti MC, Salvador A, Berna A. Supercritical fluid extraction and HPLC determination of relevant polyphenolic compounds in grape skin. J Sep Sci. 2005;28:2050–6.[Medline]
4. Manach C, Scalbert A, Morand C, Remesy C, Jimenez L. Polyphenols: food sources and bioavailability. Am J Clin Nutr. 2004;79:727–47.
5. Krasnow MN, Murphy TM. Polyphenol glucosylating activity in cell suspensions of grape (Vitis vinifera). J Agric Food Chem. 2004;52:3467–72.[Medline]
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