The contribution of each phytochemical to the total antioxidant capacity of apples was determined. Major phenolic phytochemicals of six apple cultivars were identified and quantified, and their contributions to total antioxidant activity of apples were determined using a 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical scavenging assay and expressed as vitamin C equivalent antioxidant capacity (VCEAC). Average concentrations of major phenolics and vitamin C in six apple cultivars were as follows (mg/100 g of fresh weight of apples): quercetin glycosides, 13.20; procyanidin B(2), 9.35; chlorogenic acid, 9.02; epicatechin, 8.65; phloretin glycosides, 5.59; vitamin C, 12.80. A highly linear relationship (r (2) > 0.97) was attained between concentrations and total antioxidant capacity of phenolics and vitamin C. Relative VCEAC values of these compounds were in the order quercetin (3.06) > epicatechin (2.67) > procyanidin B(2) (2.36) > phloretin (1.63) > vitamin C (1.00) > chlorogenic acid (0.97). Therefore, the estimated contribution of major phenolics and vitamin C to the total antioxidant capacity of 100 g of fresh apples is as follows: quercetin (40.39 VCEAC) > epicatechin (23.10) > procyanidin B(2) (22.07) > vitamin C (12.80) > phloretin (9.11) > chlorogenic acid (8.75). These results indicate that flavonoids such as quercetin, epicatechin, and procyanidin B(2) rather than vitamin C contribute significantly to the total antioxidant activity of apples.

The daily intake of total phenolics, total flavonoids and antioxidants in the American diet was estimated from the most common 34 fresh fruit and vegetables and their daily consumption data. Among 14 fruit and 20 vegetables, orange contributed the highest amount of total phenolics [117.1 mg gallic acid equivalent (GAE) person −1 day −1 ] and antioxidants [146.6 mg vitamin C equivalents (VCE) person −1 day −1 ]. Orange contributed about 26 and 25% of total phenolics and antioxidant, respectively, in the daily consumption of fruit and vegetables. Apples showed relatively high levels of total phenolics and antioxidant capacity comparable to those of oranges and their phenolics and antioxidants contribution is the second highest. Even though potatoes had lower levels of phenolics and antioxidant capacity, they were third due to the fact that their consumption is the highest (137.9 lb person −1 year −1 ) in the American diet. Although plums and strawberries were ranked as the group with the highest total phenolics and antioxidant capacity among 34 tested fruit and vegetables, their contributions were relatively low due to their lower daily consumption. Generally, the levels of total phenolics, total flavonoids and antioxidant capacity of fruits were higher than those of vegetables. American daily intake of phenolics, flavonoids and antioxidants from fruits and vegetables was estimated to be 450 mg GAE, 103 mg catechin equivalents and 591 mg VCE, respectively. Although we do not yet know the required minimum daily amounts of antioxidants, when we estimate the daily requirement of antioxidants, we must consider not only the antioxidant concentrations of the particular food, but also the daily intakes of the food.

Phenolic compounds have been determined by HPLC in the flesh and skin of three apple cultivars (Golden Delicious, Empire, Rhode Island Greening) during maturation and cold storage. The main phenolic compounds in all three apple cultivars were found to be epicatechin and procyanidin B2, rather than chlorogenic acid which previously had been reported as the major phenolic compound in apples. The concentration of individual phenolics in apple flesh decreased sharply during the early stage of development and then remained relatively constant during maturation and storage. There was a direct correlation between concentration of polyphenols in the flesh and in the skins. The tendency to brown decreased throughout the fruit development and maturation period.The enzymatic browning of fresh and processed fruits is a major problem for the industry. Discoloration of apple tissue is mainly due to oxidation of phenolic compounds by polyphenoloxidase (PPO). The rate of the enzymatic browning in apples depends on the PPO activity and polyphenol concentration (Harel et al., 1964;CoSeteng and Lee, 1987). Some studies have shown that chlorgenic acid is the major phenolic compound in apples and that it decreases rapidly during the early stage of fruit development to reach an almost steady level at maturity (Walker, 1963;Vamos-Vigyazo et al., 1976). The total phenol concentration in apples is reported to stay at a relatively constant level during storage (Harel et al., 1966;CoSeteng and Lee, 1987). However, some individual phenolic compounds, such as catechins (Mosel and Herman, 1974;Kolesnik et al., 1977) and chlorogenic acid (Walker, 1962;CoSeteng and Lee, 1987), have been reported to change in concentration during storage.Since individual phenolic compounds have been shownto vary in their browning rates (Oleszek et al., 1989), it is important to know the concentration of individual phenolics in apples and their changes during maturation and storage. This was the purpose of this study.

Clinical trials of several neurodegenerative diseases have increasingly targeted the evaluation of various antioxidants' effectiveness. The human diet contains several thousand phytochemicals, many of which have significant bioactivities. Vitamin C, a naturally occurring antioxidant, is known to reduce the risk of neurodegenerative disorders such as Alzheimer's disease. Quercetin, one of the major flavonoids in some fruits and vegetables, has much stronger antioxidative and anticarcinogenic activities than vitamin C. Therefore, we investigated the protective effects of quercetin on hydroxy peroxide-induced neurodegeneration. To determine the protective effects, PC12 cells were preincubated with quercetin and vitamin C before H(2)O(2) treatment for 2 h. Results showed that cell viability was clearly improved with quercetin, and quercetin showed a higher protective effect than vitamin C. Because oxidative stress is known to increase neuronal cell membrane breakdown, we further investigated lactate dehydrogenase and trypan blue exclusion assays. We observed that quercetin decreased oxidative stress-induced neuronal cell membrane damage more than vitamin C. These results suggest that quercetin, in addition to many other biological benefits, contributes significantly to the protective effects of neuronal cells from oxidative stress-induced neurotoxicity, such as Alzheimer disease.

Because strawberries are known to contain higher concentrations of phytochemicals and have higher antioxidant capacity among common fruits, their neuroprotective activity was tested in vitro on PC12 cells treated with H2O2. Their protective effect and antioxidant capacity were also compared with those of banana and orange, which are the fresh fruits consumed at highest levels in the United States. The cell viability test using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) reduction assay showed that strawberry phenolics significantly reduced oxidative stress-induced neurotoxicity. Because oxidative stress is also known to increase neuronal cell membrane breakdown, lactate dehydrogenase (LDH) and trypan blue exclusion assays were also performed. Strawberry showed the highest cell protective effects among the samples. The overall relative neuronal cell protective activity of three fruits by three tests followed the decreasing order strawberry > banana > orange. The protective effects appeared to be due to the higher phenolic contents including anthocyanins, and anthocyanins in strawberries seemed to be the major contributors.

The free radical scavenging activities of two major flavonoids (baicalein and baicalin) in Scutellaria baicalensis were determined. The antioxidant capacities of baicalein and baicalin were determined by the 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid)(*)(-) scavenging assay and showed about 110 and 70% vitamin C equivalent antioxidant capacity, respectively. Because amyloid beta (Abeta) protein is known to increase free radical production and lipid peroxidation in PC12 nerve cells, leading to apoptosis and cell death, treatment with baicalein and baicalin may result in the prevention of cellular damage by the Abeta-induced reactive oxygen species. We found that baicalein and baicalin resulted in a dose-dependent anti-Abeta toxicity by means of three different assays [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction, lactate dehydrogenase release, and trypan blue exclusion assays]. These results suggest that baicalein as well as baicalin can reduce the cytotoxicity of Abeta protein in PC12 cells, possibly by a reduction of oxidative stress, and these flavonoids may be useful in the chemoprevention of Alzheimer's disease.

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To study the effect of polyphenolics on antioxidant activities of cabbages, the amounts of total phenolics, total flavonoids, antioxidant capacity and individual phenolic compounds in raw and processed cabbages were determined. Fresh and pickled red cabbages exhibited the highest total phenolic contents (393.1+/-10.8 mg and 366.3+/-3.6 mg gallic acid equivalents/100 g fresh sample, respectively). Fresh and pickled red cabbages were also highest in flavonoids (108.1+/-9.3 mg and 72.4+/-4.4 mg catechin equivalents/100 g fresh sample, respectively). The antioxidant capacity (expressed as vitamin C equivalent antioxidant capacity) ranged from 57.1 to 695.6 mg vitamin C equivalents/100 g fresh sample, where raw and pickled red cabbages exhibited the highest antioxidant capacity. There was a good linear relationship between the total phenolics and antioxidant capacity (r2=0.9743), and between the total flavonoids and antioxidant capacity (r2=0.9557); however, the relationship between the ascorbic acid content and antioxidant capacity was very low (r2=0.1442). The antioxidant capacity of raw and processed cabbages was highly correlated with their contents of polyphenolics. Kaempferol, quercetin, and apigenin were the major flavonoids existing in cabbages except for raw and pickled red cabbages, where cyanidin was the predominant flavonoid (73.6-117.7 mg/kg). In the red cabbages, cyanidin was the major contributor to the antioxidant capacity as well as the content of total phenolics and flavonoids.