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Phytonutrients : Carotenoids and Flavonoids


            The most exciting research in the last decade has been the discovery of a group of protective nutrients called phytonutrients, naturally occurring compounds that give fruits and vegetables their bright colors (Shahidi & Ho, 1999). Phytochemicals are certain organic components of plants which scientists have isolated as being beneficial to human health in a different way from traditional anti-oxidants. They are sometimes referred to as phytonutrients, but unlike the traditional nutrients like protein, fat, vitamins, and minerals, they are not "essential" for life so the term phytochemical is more accurate. Phytochemicals have proven to be beneficial in many ways. They may serve as anti-oxidants in a bodily system when required.  For example, the phytochemical beta-carotene can metabolize to create vitamin A, a powerful anti-oxidant. Additionally, phytochemicals may enhance immune response and cell-to-cell communication, allowing for the body's built-in defenses to work more efficiently. Phytochemicals may even alter estrogen metabolism, cause cancer cells to die, repair DNA damage caused by smoking and other toxic exposure, and detoxify carcinogens by working with bodily enzymes. 

Some of the common classes of phytochemicals include carotenoids, flavonoids, phenols and terpenes. Of all the phytochemicals, the most popular are the carotenoids, the red, orange and yellow pigments found in fruits and vegetables. Carotenoids are actually a subclass of a phytochemical called terpenes, probably the most common of all the phytochemicals. Terpenes can be found in almost all plant life and have a beneficial function within plants themselves; in humans, they also seem to battle against certain cancers and even heart disease. The subclass carotenoids include alpha- and beta- carotene, beta-cryptoxanthin, and lutein, found in carrots, leafy green and yellow vegetables, and citrus or pulpy fruits. Another cartenoid, lycopene, is found heavily in tomatoes. There have been several studies suggesting that these compounds are among the most beneficial components of fruits and vegetables.  They hels plants fight oxidative stress. At first, beta-carotene from carrots was thought to be the most important phytonutrient.  More recent research broadened the study to include the entire family of carotenoids, a family of naturally occurring fat soluble antioxidants that make up the yellow, orange, and red colors in many foods like squash, canteloupe, and strawberries.  Cooking does not destroy them and usually increases availability.  Many are fat soluble, so the meal should include a source of oil.  Carotenoids can be found in  yellow-orange fruits and vegetables, green vegetables.  Lutein and zeaxanthin are available in dark green vegetables especially kale, collard greens, spinach and turnip greens.  Lycopene is available in red fruits and vegetables, especially tomatoes.

On the other hand, flavonoids form another family of phytonutrients and they come from grapes, berries, lemons, grapefruits and teas were also discovered to have their own benefits.  There are quite a variety of these including over 60 in citrus.  There uses appear to be wide ranging, e.g., antiinflammatory, antitumor, antiviral.  They help those with coronary and cholesterol problems.  They can be found mostly in vegetables and fruits, pine bark, green tea, and wine

Tufts Nutrition's Antioxidants Research Laboratory is exploring the effect of antioxidant polyphenols, particularly the flavonoids, on changes in oxidative stress status associated with aging and chronic conditions such as diabetes, heart disease, and age-related macular degeneration (AMD). Lipid, protein, nucleic acids, and other cellular targets of oxidative damage are being assessed in experimental models and human studies to elucidate antioxidant requirements for optimal health. In-vitro studies have indicated that some flavonoids have a marked synergistic interaction with vitamin E in reducing selected measures of oxidative stress in human lipoproteins. Current investigations include examinations of the bioavailability and antioxidant capacity of flavonoids in healthy older adults as well as in diabetics. Flavonoids from almonds, bilberry, chocolate, green tea, and oats are also being tested (Cappellano, 1998).

The Laboratory for Nutrition and Vision Research and the Nutritional Epidemiology Program's epidemiological studies have found that antioxidant vitamins are associated with a reduced risk of the development and progression of cataracts and AMD.  These observations are now being extended to associations with carotenoid and flavonoid intakes. 

Moreover, the Gastrointestinal Nutrition Laboratory researchers have found increases in macular pigment density in the central area of the retina following consumption of spinach and corn, foods rich in the carotenoids lutein and zeaxanthin. High concentrations of this pigmentation have been linked to a decreased risk of AMD.  Studies of gender differences in lutein metabolism have shown a significant negative correlation between adipose tissue lutein concentrations and macular pigment for women, but a significant positive relation for men. Studies are exploring the bioavailability of lutein from egg yolks, vegetables, and dietary supplements as well as the effect of supplemental lutein and docosahexaenoic acid on visual function in the elderly.  The consumption of foods rich in provitamin A has been suggested as a realistic and sustainable means to overcome vitamin A deficiency in less-developed countries. To determine the vitamin A value of plant provitamin A carotenoids, vegetables were grown hydroponically with stable isotopes and fed to volunteers. The bioconversion of carotenes to vitamin A from different foods containing equal amounts of provitamin A carotenoids was found to vary with the vegetable tested.  The formulation of other carotenoids was found to affect bioavailability when researchers observed absorption of synthetic lycopene three times higher than lycopene from cooked and pureed tomatoes. Advanced mass spectrophotometric methods are used to determine both intact carotenoids and their various metabolic products from intrinsically labeled food in blood and tissue taken from human subjects (Cappellano, 1995). 

Furthermore, nhe Neuroscience Laboratory research has revealed that both aging healthy mice and transgenic mice with mutations important to Alzheimer's Disease (amyloid precursor protein and presenilin-1) perform better in a series of cognitive function tests when fed a diet containing extracts from blueberry. Mice fed blueberry extract also showed significantly greater neuronal signal ing.  Anthocyanin flavonoids from blueberry also appear to protect nerve cells in culture from amyloid beta and oxidative stress.  These and related research projects at Tufts Nutrition are helping to define the role of phytochemicals in human health and suggest ways to enhance the value of food products and substantiate improved dietary guidelines.


Experimental design

The researcher can use two experimental designs for this study.  First, advanced mass spectrophotometric methods can be used to determine both intact carotenoids and flavonoids and their various metabolic products from intrinsically labeled food in blood and tissue taken from animal subjects like mice

The researcher will form two experimental groups, one for aging healthy mice and the other for transgenic mice with mutations important to Alzheimer's Disease (amyloid precursor protein and presenilin-1),  They will be fed a diet containing extracts from blueberry.  One group of mice will be fed with the blueberry extract, while the control group with placebo.  The researcher will find out the performance of both groups of mice through a series of cognitive function tests, specifically finding out which has neuronal signaling and which can protect nerve cells in culture from amyloid beta and oxidative stress.


All variables are assumed to be normally distributed and data will be expressed as means±S.D. Within-group differences during the prospective study will be analyzed by one-way ANOVA for repeated measures, followed by a paired t test with a significant (P < 0.05) difference within a group.  The performance of both groups of mice through a series of cognitive function tests, specifically finding out which has neuronal signaling will be measured through a two-way repeated measures ANOVA. Differences between groups in any variable will be assessed with unpaired t tests. Relationships between variables will be analyzed with simple linear regression and stepped multiple regression, and groups will be entered as a continuous dummy variable where necessary. Data will be analyzed on commercially available software (Stat View).


The use of animals in research and testing is vital, including this study.  However, it only makes up about 10% of all biomedical research and testing (Beauchamp & Walters, 1999).  Animal research is one step in a complex process that aims to advance biological and medical understanding. Similarly, safety testing using animals is one of several types of test that aims to protect humans, animals and the environment.   Advances in science and technology can lead to techniques that can replace animals. Moreover, cell cultures provide useful information.  New non-invasive scanning techniques make it possible to study blood flow or nerve activity in the living human brain, for instance.  Furthermore, genetic studies are a growing area of research, and may be carried out at molecular and cellular levels.  Better production methods for biological substances like insulin mean that high tech equipment can be used for quality control in many cases instead of using animals.  Finally, computers and chemical techniques can screen out harmful or useless compounds before they ever get to the animal testing stage.  Most of these advances in science and technology have led to a welcome reduction in the numbers of animals used, to about half the number used 20 years ago.


This discussion emphasizes the importance of flavonoid and carotenoid research.  Both, flavonoids and carotenoids, may act as efficient antioxidants in vitro and in foods, depending on the system and on the oxidative challenge. A scheme explaining the antioxidant and prooxidant behaviour of flavonoids has been elaborated. Flavonoids can act as antioxidants in vivo at high doses, but there may not be antioxidant effects at human dietary levels. The carotenoids, lutein and lycopene may have physiological effects related to antioxidation at human dietary levels.  Some flavonoids, but not carotenoids, have potent cytotoxic effects which may be related to prooxidant effects towards proteins at high concentrations due to interactions with transition metals. The oxidation products identified from quercetin and kaempferol are neither cytotoxic nor mutagenic.  Finally, the hepatic biotransformation of flavonoids has been elucidated, and biomarkers for human exposure have been developed and validated.

Among the goals of this study are the following: to increase the stability of foods or ready-made dishes by using ingredients rich in natural antioxidants; and to increase the quality of products based on processed fruits and vegetables by securing that natural antioxidants are not lost during the production process. This could be achieved by chemical analysis for antioxidants and/or by identifying components which enhance oxidation processes and by determining the antioxidant capacity of the products at various stages of the process.  This study will also document the increased uptake or positive short-term physiological effects of natural antioxidants from improved foods by publishing results of highquality research on the products internationally, usethe knowledge on which natural antioxidants may possess beneficial effects to provide a rationale for developing food plants rich in such components by gene technology or by traditional breeding, and increase the quality of meat and dairy products by optimising animal feeds with respect to natural antioxidants.

This study forms part of a broad area of research that contributes to man’s understanding of appropriate dietary practices throughout the life cycle and factors that affect these requirements.  The dietary practice in question involves eating food rich in carotenoids and flavonoids.  Moreover, this study aims to enrich the already avaliable research data that provides man with new insights that may affect their attitudes and behavior toward foods rich in carotenoids and flavonoids.  The following areas of research will be emphasized:  nutritional requirements including metabolism and utilization, at least among the experimented animals; the mice’s bioavailability of dietary components; identifying the mechanisms underlying the relationship between diet and optimal health, such as the effect of nutrients on the immune system, and cellular and molecular mechanisms influencing nutritional status, including nutrient effects on gene expression, focused specifically on flavonoids and carotenoieds.  In addition, this study  supports research on identification of obstacles to adopting healthful food habits with particular emphasis on factors affecting consumer attitudes and behavior and development of recommendations for interventions to improve nutritional status.  Innovative approaches to these research problems are encouraged.  Most importantly, this study hopes to educate people on the merits of including flavonoids and carotenoids in their daily diet.


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