The total phenolic content of 13 commercially available fruit juices and juice drinks, selected to represent the most popular juice flavors in the United Kingdom, were analyzed using the Folin-Ciocalteu assay. Individual phenolic compounds were identified and quantified using HPLC-PDA-MS2. The catechin content and degree of polymerization of proanthocyanidins were also analyzed. Purple grape juice contained the largest number of individual phenolic compounds and also the highest concentration of total phenolics. The main components were flavan-3-ols, anthocyanins, and hydroxycinnamates, which accounted for 93% of the total phenolic content. In contrast, white grape juice, which contained principally hydroxycinnamates, had the lowest total phenolic content. Antioxidant activity was measured using the ORAC and FRAP assays, and the data obtained were in broad agreement with total phenol content. In view of the recent findings of the Kame project indicating that long-term fruit juice consumption can provide protection against Alzheimer’s disease (Dai et al. Am. J. Med. 2006, 379, 464-475), it is suggested that the protective effects may be enhanced by consumption of a combination of juices rich in phenolics and containing a diverse variety of individual phenolic compounds, namely, juices derived from purple grapes, grapefruit, cranberries, and apples.

Plant Products and Human Nutrition Group, Graham Kerr Building, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, United Kingdom.

Lutein (from Latin lutea meaning “yellow”) is one of over 600 known naturally occurring carotenoids. Found in green leafy vegetables such as spinach and kale, lutein is employed by organisms as an antioxidant and for blue light absorption. Lutein is covalently bound to one or more fatty acids present in some fruits and flowers, notably marigolds.

Lutein was found to be present in a concentrated area of the macula, a small area of the retina responsible for central vision. The hypothesis for the natural concentration is that lutein helps protect from oxidative stress and high-energy light. Various research studies have shown that a direct relationship exists between lutein intake and pigmentation in the eye. Several studies also show that an increase in macula pigmentation decreases the risk for eye diseases such as Age-related Macular Degeneration (AMD).

Lutein is a natural part of human diet when fruits and vegetables are consumed. For individuals lacking sufficient lutein intake, lutein-fortified foods are available, or in the case of elderly people with a poorly absorbing digestive system, fortification via a sublingual spray ensures maximum benefit to the eyes. As early as 1996, lutein has been incorporated into dietary supplements. While no recommended daily allowance currently exists for lutein as for other nutrients, positive effects have been seen at levels of 6 mg/day. The only definitive side effect of excess lutein consumption is the same observed for β-carotene overdose, namely bronzing of the skin (carotenodermia). The normal levels of Lutein found in a daily vitamin tablet can be as low as 0.25 mg.

Flavonoids (bioflavonoids in the media) are phenylpronanoids, a class of plant-derived organic compounds that are biosynthesized from the amino acid phenylalanine and belonging to the polyphenol group, characterized by the presence of more than one phenol group per molecule. Flavonoids are most commonly known for their antioxidant activity.

Vitamin C or L-ascorbate is an essential nutrient required to allow a range of essential metabolic reactions in animals and plants, and widely known as the vitamin that prevents scurvy in humans. The pharmacophore of vitamin C is the ascorbate ion. In living organisms, ascorbate is an antioxidant, as it protects the body against oxidative stress, and a cofactor in several vital enzymatic reactions. As a nutrient, its uses and requirements are matters of on-going debate. The North American Dietary Reference Intake recommends 90 milligrams per day and no more than 2 grams per day (2000 milligrams per day). As a food additive, vitamin C is used as an antioxidant preservative and an acidity regulator. Several E numbers account for the vitamin, depending on its chemical structure: E300 as ascorbic acid, E301 as sodium ascorbate, E302 as calcium ascorbate, and E303 as potassium ascorbate.

Retinol, the animal form of vitamin A, is a yellow fat-soluble, antioxidant vitamin important in vision and bone growth. It belongs to the family of chemical compounds known as retinoids. Retinol is ingested in a precursor form; animal sources (milk and eggs) contain retinyl esters, whereas plants (carrots, spinach) contain pro-vitamin A carotenoids. Hydrolysis of retinyl esters results in retinol while pro-vitamin A carotenoids can be cleaved to produce retinal. Retinal, also known as retinaldehyde, can be reversibly reduced to produce retinol or it can be irreversibly oxidized to produce retinoic acid. The best described active retinoid metabolites are 11-cis-retinal and the all-trans and 9-cis-isomers of retinoic acid.

The study was led by the Cochrane Hepato-Biliary Group at Copenhagen University Hospital in Denmark. The researchers first analyzed 68 studies involving 232,606 people and found no significant effect on mortality — neither good nor bad — linked to taking antioxidants. When they eliminated the lower-quality studies and looked only at the most trustworthy ones, they actually found a higher risk of death for people taking vitamins: 4 percent for those taking vitamin E, 7 percent for beta-carotene and 16 percent for vitamin A. The actual cause of death in most studies was unknown, however. Those findings are based on an analysis of 47 studies involving 180,938 people who were randomly assigned to get real vitamins or dummy pills. Some involved superdoses far exceeding the recommended daily amount of the compounds; others involved normal doses. The study’s senior author, Dr. Christian Gluud of Copenhagen University Hospital, said, “The main message is that prevention by beta carotene, vitamin A and vitamin E cannot be recommended. These three antioxidant supplements may increase mortality.”

Mortality in randomized trials of antioxidant supplements for primary and secondary prevention: systematic review and meta-analysis.
JAMA. 2007 Feb 28;297(8):842-57. Review.
PMID: 17327526 [PubMed - indexed for MEDLINE]