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  • A study from the Linus Pauling Institute showed that eating large amounts of apples did not result in that antioxidant benefits of apple polyphenol extracts.

  • In one human study, apple polyphenols increased the activity of SOD (superoxide dismutase), one of your body's most important and powerful natural antioxidants, by 41%.

  • An unpublished paper from Japan,  available exclusively to our readers, points out that polyphenols from apples are among the few known water-soluble plant polyphenols.

  • Italian researchers report that the apples may have lost much of their health benefit before they reach your grocery store.

  • Polyphenols may not be absorbed at all in the presence of sugar molecules, say researchers in the Netherlands, strengthening the case for apple polyphenol extracts.

Relevance of apple polyphenols as antioxidants in human plasma: contrasting in vitro and in vivo effects, Free Radic Biol Med. 2004
Effects of Phenol-Depleted and Phenol-Rich Diets on Blood Markers of Oxidative Stress, and Urinary Excretion of Quercetin and Kaempferol in Healthy Volunteers, Journal of the American College of Nutrition, 2003
Cold-storage affects antioxidant properties of apples in Caco-2 cells, J Nutr. 2004
High-throughput fluorescence screening of antioxidative capacity in human serum, Anal Biochem. 2001
Apple and pear peel and pulp and their influence on plasma lipids and antioxidant potentials in rats fed cholesterol-containing diets, J Agric Food Chem. 2003 Sep
Comparative content of some bioactive compounds in apples, peaches and pears and their influence on lipids and antioxidant capacity in rats, J Nutr Biochem. 2002
Antioxidant Component and Biological Regulatory Functions in Apple Polyphenols, Akio Yanagida, unpublished
Absorption, metabolism and health effects of dietary flavonoids in man, Biomed Pharmacother. 1997


Free Radic Biol Med. 2004 Jan 15;36(2):201-11
Relevance of apple polyphenols as antioxidants in human plasma: contrasting in vitro and in vivo effects.

Lotito SB, Frei B.

Linus Pauling Institute, Oregon State University, Corvallis, OR 97331, USA.

Apples are a major source of flavonoids in the Western diet, and flavonoid-rich foods may help protect against chronic diseases by antioxidant mechanisms. In the present study we investigated: (1) the antioxidant capacity of representative apple polyphenols and their contribution to the total antioxidant capacity of apple extracts; (2) the effects of adding apple extract to human plasma in vitro on oxidation of endogenous antioxidants and lipids; and (3) the effects of apple consumption by humans on ex vivo oxidation of plasma antioxidants and lipids. We found that the apple-contained flavonols and flavanols, quercetin, rutin, (-)-epicatechin, and (+)-catechin, had a higher antioxidant capacity than the dihydrochalcones, phloridzin and phloretin, and the hydroxycinnamate, chlorogenic acid. However, together these apple polyphenols contributed less than 20% to the total antioxidant capacity of aqueous apple extracts. When human plasma was exposed to a constant flux of aqueous peroxyl radicals, endogenous ascorbate (70.0 +/- 10.3 microM) was oxidized within 45 min of incubation, while endogenous urate (375 +/- 40 microM) and alpha-tocopherol (24.7 +/- 1.2 microM) were oxidized after ascorbate. Addition of 7.1 or 14.3 micrograms/ml total phenols of apple extract did not protect ascorbate from oxidation, but increased the half-life (t1/2) of urate from 136 +/- 15 to 192 +/- 16 and 208 +/- 23 min, respectively (p < 0.05 each), and t1/2 of alpha-tocopherol from 141 +/- 18 to 164 +/- 8 min (p = ns) and 188 +/- 8 min (p < 0.05). Lipid peroxidation started after ascorbate depletion, and addition of apple extract increased the lag time preceding detectable lipid peroxidation from 36.3 +/- 3.7 to 50.9 +/- 2.7 min (p < 0.05) and 70.4 +/- 4.2 min (p < 0.001). However, when six healthy volunteers ate five apples and plasma was obtained up to 4 h after apple consumption, no significant increases in the resistance to oxidation of endogenous urate, alpha-tocopherol, and lipids were found. Thus, despite the high antioxidant capacity of individual apple polyphenols and apple extracts and the significant antioxidant effects of apple extract added to human plasma in vitro, ingestion of large amounts of apples by humans does not appear to result in equivalent in vivo antioxidant effects of apple polyphenols.

PMID: 14744632 [PubMed - indexed for MEDLINE]


Journal of the American College of Nutrition, Vol. 22, No. 3, 217-223 (2003)

Effects of Phenol-Depleted and Phenol-Rich Diets on Blood Markers of Oxidative Stress, and Urinary Excretion of Quercetin and Kaempferol in Healthy Volunteers

Hwa-Young Kim, MSc, Ok-Hee Kim, PhD and Mi-Kyung Sung, PhD

Department of Food and Nutrition, Sookmyung Women’s University (H.-Y.K., M.-K.S.), Seoul, KOREA
National Institute of Toxicological Research, Korea Food and Drug Administration (O.-H.K.), Seoul, KOREA

Address reprint requests to: Mi-Kyung Sung, Ph.D., Associate Professor, Department of Food and Nutrition, Sookmyung Women’s University, 53-12 Chungpa-dong 2-ka, Yongsan-ku Seoul, 140-742, KOREA. Email:

Objective: Epidemiological studies have suggested beneficial effects of dietary polyphenols in reducing the risk of chronic diseases. This study was performed to investigate the effects of polyphenol-depleted and polyphenol-rich diets on blood oxidative stress markers and urinary excretions of major phenols.

Methods: Nineteen healthy female non-smokers 19 to 21 years of age took part in the study, which consisted of two dietary intervention periods separated by three days. Experimental diets were composed of common foods selected to comply with low contents of polyphenols for phenol-depleted intervention and high contents of polyphenols for phenol-rich diets. Blood and urine samples were collected on day 0, 3 and 6 of each intervention. Duplicate portions of foods provided to the subjects were also collected. Blood oxidative stress markers included plasma antioxidant vitamins, erythrocyte superoxide dismutase (SOD) activity and lymphocyte DNA damage. Urinary excretions of major phenols were measured to affirm bioavailability of dietary phenols.

Results: Plasma -tocopherol and ß-carotene concentrations were slightly decreased on day 3 and 6 of the phenol-depleted dietary intervention period, although no change was observed with phenol-rich diets. The erythrocyte SOD activity was also slightly decreased during phenol-depleted dietary intervention. However, at day 6 of the phenol-rich intervention, the activity of SOD was significantly increased by 41%. Tail moment and tail length of lymphocyte DNA as markers of DNA damage were higher on day 6 of phenol-depleted intervention, although only tail moment showed a statistical significance. The average intakes of quercetin and kaempferol during the phenol-rich intervention were 21 mg/day and 9 mg/day, respectively. The average urinary excretion rates during phenol-rich intervention were 2.06% for quercetin and 0.46% for kaempferol. There were positive correlations between erythrocyte SOD activity and urinary concentration of quercetin or kaempferol.

Conclusions: These results suggest that polyphenol-rich diets may decrease the risk of chronic diseases by reducing oxidative stress.


J Nutr. 2004 May;134(5):1105-9.
Cold-storage affects antioxidant properties of apples in Caco-2 cells.

Tarozzi A, Marchesi A, Cantelli-Forti G, Hrelia P.

Department of Pharmacology, University of Bologna, 40126 Bologna, Italy.

Data on the composition of phenolic antioxidant compounds present in food plants and assessment of their activity are essential for epidemiological explanation of the health benefits of fruit and vegetables. Various factors such as cultivation methods, industrial processing, and storage may affect the final concentrations of phytochemicals in food plants and their eventual bioactivity. This study investigated the influence of commercial cold-storage periods on the antioxidant properties of apples grown either by organic or integrated systems. In both cases, total phenolics and total antioxidant activity decreased only in the first 3 mo and only in apples with skin (P < 0.05), suggesting that cold storage rapidly impoverishes these properties in skin but not in pulp. Assessment of antioxidant bioactivity in vitro, measured in terms of intracellular antioxidant, cytoprotective, and antiproliferative activity in human colon carcinoma (Caco-2) cells (differentiated to normal intestinal epithelia for intracellular antioxidant and cytoprotective effects), showed strong, time-related decreases over 6 mo of cold storage for all 3 parameters (P < 0.01), irrespective of the cultivation system. These findings with integrated and organic apples further support the concept that organic systems of cultivation do not generally provide real health benefits. Moreover, the data from the present study clearly show that factors such as cold storage may affect the antioxidant properties of apples. Epidemiological studies on the cancer-preventive benefits of fruits and vegetables should take into account the cold-storage bias for apples, and possibly for other products.

PMID: 15113953 [PubMed - indexed for MEDLINE]


Anal Biochem. 2001 Oct 15;297(2):144-53

High-throughput fluorescence screening of antioxidative capacity in human serum.

Mayer B, Schumacher M, Brandstatter H, Wagner FS, Hermetter A.

Department of Biochemistry, Technische Universitat Graz, Graz, A-8010, Austria.

Diphenylhexatriene-labeled phosphatidylcholine and propionic acid have been established as selective fluorescence markers for the continuous determination of oxidation processes in the lipid and aqueous phases of unfractionated human serum. Oxidation of the respective fluorophores leads to a decrease in fluorescence intensity from which the time-dependent degradation of the marker molecule can be determined. The lag times preceding the propagation of oxidation are representative for the antioxidative capacity of the system, which may be influenced by exogenous factors, e.g., the antioxidants from the diet. Supplementation of human serum by quercetin, rutin, vitamin E, vitamin C, or total apple phenolics in vitro led to a decrease in oxidizability depending on the oxidation marker and the hydrophobicity of the antioxidant. Quercetin and vitamin E showed a higher in vitro capacity of protecting lipoproteins against oxidation. In contrast, rutin and vitamin C were more efficient as inhibitors in the aqueous phase. The same effect on serum was found after dietary consumption of apples. This result is in line with the known observation that intake of plant polyphenols leads to an increase in serum levels of hydrophilic antioxidants. Copyright 2001 Academic Press.

Publication Types:

·         Clinical Trial

PMID: 11673881 [PubMed - indexed for MEDLINE]

J Agric Food Chem. 2003 Sep 10;51(19):5780-5.

Apple and pear peel and pulp and their influence on plasma lipids and antioxidant potentials in rats fed cholesterol-containing diets.

Leontowicz M, Gorinstein S, Leontowicz H, Krzeminski R, Lojek A, Katrich E, Ciz M, Martin-Belloso O, Soliva-Fortuny R, Haruenkit R, Trakhtenberg S.

Department of Animal Physiology, Faculty of Veterinary Medicine, Warsaw Agricultural University, Nowoursynowska 166, 02-787 Warsaw, Poland.

The aim of this study was to assess the bioactive compounds of apple and pear peel and pulp in vitro and their influence on plasma lipids and antioxidant potentials in vivo. The antioxidant potentials measured by 1,1-diphenyl-2-picrylhydrazyl (DPPH), beta-carotene bleaching (beta-carotene), and nitric oxide inhibition radical scavenging (NO) tests in apple peel and pulp were significantly higher than in pear peel and pulp, respectively. The ethanol extract of apple peels showed the strongest inhibition of lipid peroxidation as a function of its concentration and was comparable to the antioxidant activity of butylated hydroxyanisole. The pear pulp extract had the weakest antioxidant ability, whereas other extracts such as apple pulp and pear peel were nearly equal. The antioxidant activities comprised contributions from polyphenols, phenolic acids, and flavonoids and correlated well with polyphenols and flavonoids. The correlation coefficients between polyphenols and antioxidant activities by DPPH, beta-carotene, and NO were as follows: 0.9207, 0.9350, and 0.9453. Contrarily, the correlation coefficient between the content of dietary fiber and the antioxidant activities test was low. The content of all studied indices in apple and pear peel was significantly higher than in peeled fruits (p < 0.05). Diets supplemented with fruit peels exercised a significantly higher positive influence on plasma lipid levels and on plasma antioxidant capacity of rats than diets with fruit pulps.

PMID: 12952433 [PubMed - indexed for MEDLINE]

J Nutr Biochem. 2002 Oct;13(10):603-610.

Comparative content of some bioactive compounds in apples, peaches and pears and their influence on lipids and antioxidant capacity in rats.

Leontowicz H, Gorinstein S, Lojek A, Leontowicz M, Ci;z M, Soliva-Fortuny R, Park YS, Jung ST, Trakhtenberg S, Martin-Belloso O.

Department of Physiology, Biochemistry, Pharmacology and Toxicology, Faculty of Veterinary Medicine,
Warsaw Agricultural University, Nowoursynowska 166, 02-787, Warsaw, Poland

The aim of this study was to compare some bioactive compounds in apples, peaches and pears and their influence on lipids and antioxidant capacity in rats. The content of total polyphenols (g/100g) was 0.23 +/- 0.03; 0.22 +/- 0.03 and 0.68 +/- 0.1 in peeled fruits and 0.48 +/- 0.04, 0.47 +/- 0.04 and 1.2 +/- 0.12 in peels of peaches, pears and apples, respectively. Caffeic, p-coumaric and ferulic acids and the total radical-trapping antioxidative potential (TRAP) values in peeled apples and their peels were significantly higher than in peaches and pears, respectively. Contrarary, no significant differences in the content of dietary fiber among the studied fruits were found. The content of all studied indices in peels was significantly higher than peeled fruits (p < 0.05 ). A good correlation between the total polyphenols and the TRAP values was found in all fruits. Diets supplemented with apples and to a less extent with peaches and pears have improved lipid metabolism and increased the plasma antioxidant potential especially in rats fed with added cholesterol. The highest content of biologically active compounds and the best results in the experiment on rats makes apple preferable for dietary prevention of atherosclerosis and other diseases.

PMID: 12550072 [PubMed - as supplied by publisher]

Nikka Whiskey Distilling Company, Ltd., Chiba Japan
Antioxidant Component and Biological Regulatory Functions in Apple Polyphenols

Akio Yanagida, Institute for Product Research and Development, Nikka Whiskey Distilling Company, Ltd., Chiba Prefecture, Japan

(Mr. Yanagida is a principal member of product research and development for this Japanese company, a leader in the development of extraction, purification, and commercial applications of apple polyphenol extracts in Japan. We have obtained this unpublished paper through private channels.)

Excerpts: "Apples contain high concentrations of polyphenol compounds that have high water solubility."

"Another characteristic of apple condensed tannins (ACT, catechin polymers) is significantly higher water solubility compared to catechin monomers. In general, many plant polyphenols are water-insoluble, and polyphenols with easy solubility in pure water are quite rare. Thus, this ACT characteristic is especially noteworthy."

Biomed Pharmacother. 1997;51(8):305-10.
Absorption, metabolism and health effects of dietary flavonoids in man.

Hollman PC, Katan MB.

DLO State Institute for Quality Control of Agricultural Products (RIKILT-DLO), Wageningen, The Netherlands.

Flavonoids are polyphenolic compounds that occur ubiquitously in foods of plant origin. Over 4,000 different flavonoids have been described, and they are categorized into flavonols, flavones, catechins, flavanones, anthocyanidins and isoflavonoids. Flavonoids have a variety of biological effects in numerous mammalian cell systems, in vitro as well in vivo. Recently, much attention has been paid to their antioxidant properties and to their inhibitory role in various stages of tumour development in animal studies. Quercetin, the major representative of the flavonol subclass, is a strong antioxidant, and prevents oxidation of low density lipoproteins in vitro. Oxidized low density lipoproteins are atherogenic, and are considered to be a crucial intermediate in the formation of atherosclerotic plaques. This agrees with observations in epidemiological studies that the intake of flavonols and flavones was inversely associated with subsequent coronary heart disease. However, no effects of flavonols on cancer were found in these studies. The extent of absorption of flavonoids is an important unsolved problem in judging their many alleged health effects. Flavonoids present in foods were considered non-absorbable because they are bound to sugars as beta-glycosides. Only free flavonoids without a sugar molecule, the so-called aglycones, were thought to be able to pass through the gut wall. Hydrolysis only occurs in the colon by microorganisms, which at the same time degrade flavonoids. We performed a study to quantify absorption of various dietary forms of quercetin. To our surprise, the quercetin glycosides from onions were absorbed far better than the pure aglycone. Subsequent pharmacokinetic studies with dietary quercetin glycosides showed marked differences in absorption rate and bioavailability. Absorbed quercetin was eliminated only slowly from the blood. The metabolism of flavonoids has been studied frequently in various animals, but very few data in humans are available. Two major sites of flavonoid metabolism are the liver and the colonic flora. There is evidence for O-methylation, sulphation and glucuronidation of hydroxyl groups in the liver. Bacterial ring fission of flavonoids occurs in the colon. The subsequent degradation products, phenolic acids, can be absorbed and are found in urine of animals. Quantitative data on metabolism are scarce.

PMID: 9436520 [PubMed - indexed for MEDLINE
(more research)
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