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Carotenoids

Carotenoids are ubiquitous organic molecules found naturally within plants, fruits vegetables, and other organisms. Although they are not produced by the human body, carotenoids have been found to be essential to human health with the nutritional understanding of vitamin A (retinol) and b -carotene. Carotenoids are also important natural sources of orange, yellow, and red food coloring for the food and beverage industries.

Carrot root slices containing typical carotenes (primarily alpha- and beta-); typical carotenes plus anthocyanins; lycopene; xanthophylls

Purple roots of carrot

Cross sections of four mature fruits of high carotene cucumber (15-25 mg.kg-1 carotenes).

High carotene carrots Beta III (left roots and slices, 240-280 mg.kg-1 carotenes), HCM (right roots and slices, 430-490 mg.kg-1 carotenes), and progenitor population of Beta III (center slices, 140 mg.kg-1 carotenes).

New research has demonstrated that carotenoids may also lend additional health benefits that may possibly reduce the risk of certain types of chronic diseases, such as cancer and heart disease. The carotenoid-based food colorants are discussed with respect to their coloring characteristics in foods and the additional health benefits of carotenoids in the diet are reviewed. Carotenoids show promise as health promoting phytonutrients, however, more work is needed to determine their exact role in human health. Until then, a fruit and vegetable diet rich in micronutrients, carotenoids, and other phytonutrients is recommended. Carotenoids are organic pigments that are found in the chloroplasts of photosynthetic plants and in the chromoplasts of fruits, flowers, and leaves. They also can be found in certain animals, photosynthetic microorganisms, and algae. Over 600 carotenoids have been identified and are widely distributed in nature. In plants, carotenoids function as accessory light harvesting pigments that absorb light energy that is then transferred to chlorophyll for use in photosynthesis. Carotenoids also act as UV light scavengers, protecting plants from photooxidation and its adverse effects, preventing cell damage from singlet oxygen. Plants also use carotenoids during times of stress, injury, or severe light exposure, in order to protect plants from further infection and oxidative damage.

Carotenoids are generally composed of eight isoprene units that are covalently bonded to each other forming an extensive symmetrical conjugated double bonded molecule. This conjugated double bond structure allows carotenoids to absorb UV and white-light energy, giving them their coloring and antioxidant properties. Carotenoids may be linear (like lycopene) or contain symmetrical rings at either end of the molecule (like b -carotene) and are characterized by their structural elements as either carotenes, which are exclusively made up of hydrocarbons, or xanthophylls, which also contain oxygen. Carotenes are generally non-polar and oil soluble while xanthophylls are more polar and less oil soluble than carotenes due the presence of oxygen. The main carotenoids in the diet include b -carotene & b -carotene (carrots), lutein & zeaxanthin (spinach, kale, collard greens, broccoli), lycopene (tomatoes), and b -crypotoxanthin (oranges).

Health Properties of Carotenoids

General Modes of Action

Aerobic organisms use oxygen in their metabolism to generate energy for life and proper function. During many of these biochemical events, highly reactive oxygen species and other high-energy free radicals are sometimes created and may potentially interact with various cell fractions, including lipids, carbohydrates, proteins, and DNA, causing potential loss of their respective cell functions. In addition to endogenous sources of free radicals, external environment sources can also initiate oxidative stress on human cells from such things as smoking, UV light, X-rays, pollution, stress, strenuous exercise, and exposure to certain chemicals causing additional oxidation of healthy cells and tissue. Fortunately, cells are equipped with enzyme defense systems (superoxide dismutase, glutathione peroxidase, and catalase) to neutralize and destroy these high energy "errors" of oxidative metabolism. It is believed that oxidative stress from these highly reactive oxygen species and other free radicals are related to the onset events of the ageing process and many chronic diseases. Since many carotenoids are powerful antioxidants (particularly b -carotene, lycopene, and lutein) they (along with their metabolites) may also possibly exert their antioxidant effects when consumed in the diet and thereby help reduce the onset and risk of developing these diseases. As such, carotenoids have been found to help protect against cardiovascular disease, different cancers, age-related macular degeneration, and photosensitive disorders.

In addition to being an antioxidant, carotenoids may also act as health promoting agents by enhancing gap junction intercellular communication, act as antiinflammatory and anti-tumor promoting agents, may induce endogenous phase II detoxification enzymes, and may enhance immune function.

b -carotene/Vitamin A

Retinol (Vitamin A) is an established nutrient in humans and is essential for the maintenance of proper eyesight, the production of sperm, healthy skin and epithelial tissues, bone and tooth formation, growth, and tissue repair. It is also important in fetal development, cell differentiation, immunity, and cell division.

Other carotenoids, such as b -carotene can be converted to retinol by the body during digestion in the small intestine. Deficiencies of retinol can lead to nightblindness, poor skin, abnormal bone development, and suppressed immunity. b -carotene is also used as a treatment for the genetic disease, erythropoietic protoporphyria, a skin condition that causes extreme sensitivity to light exposure. This light sensitivity is caused by a build up of porphyrins in the skin which absorb light energy and cause the production of highly reactive singlet oxygen. These free radicals can then cause cell damage and tissue inflammation. b -carotene helps alleviate the painful symptoms of the disease by quenching singlet oxygen free radicals.

Carotenoids may also help protect against cardiovascular disease by preventing LDL oxidation. The antioxidant action of b -carotene and other carotenoids may also help reduce the incidence of cancer. A recent review of epidemiological data shows a strong inverse relationship between carotenoid-rich fruit & vegetable consumption and various site-specific cancers including lung, esophagus, stomach, colorectal, cervix, and throat cancers.

However, some intervention studies with b -carotene did not show similar positive effects on cancer incidence. In the ATBC study (Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study), 20 mg of b -carotene per day were administered to male smokers in hopes of reducing lung cancer incidence.

However, it was reported that test subjects in the b -carotene group showed greater incidence of mortality, lung, prostate, and stomach cancers. Similarly, the CARET (The b -carotene and Retinol Efficacy Trial) study administered large doses of b -carotene (30 mg/day) and retinol (25,000 IU/day) to high-risk groups for lung disease (smokers, former smokers, and asbestos workers). After four years into the study, the trial had to be suspended due to an increase in the mortality rate and lung cancer incidence. It may be that in smokers, b -carotene may act as a tumor promoter since similar higher doses of b -carotene (50 mg/alternate days)were administered over a twelve year period to primarily non-smoking healthy males in the Physicians’ Health Study and found no adverse effect or benefit in terms of cancer incidence and overall mortality. The Nutrition Intervention Trial (I) conducted in China, however, did result in lower mortality rates from stomach cancer and overall cancer over a five-year period of administering a mixture of b -carotene, -tocopherol, and selenium supplements (15 mg/day, 30 mg/day, & 50 g/day respectively).

Lutein/Zeaxanthin

Carotenoids in the diet, particularly lutein and zeaxanthin, have also been found to be important in the prevention of eye-related diseases such age-related macular degeneration (AMD) and cataracts. The macula lutea is a concentrated yellow spot on the retina of the eye that is made up of the carotenoid pigments lutein and zeaxanthin, the only dominate carotenoids found in the retina. The macula lutea is considered responsible for the major part of visual acuity and functions as a blue light filter, preventing high energy blue light from damaging the eye’s photoreceptors and maintaining the integrity of the retina. These carotenoid pigments are not made by body and can be only obtained through the diet from carotenoids rich foods, such as spinach, kale, collard green, broccoli, and squashes. Lutein and zeaxanthin may also protect the retina by acting as an antioxidant against light and metabolism induced oxidation.

Risk factors such as advanced age (65 or older), poor fruit and vegetable intake, smoking, excessive alcohol consumption, excessive sun exposure, and light eye color can increase the chances of developing AMD. Apart from iris color, all other risk factors are thought to be related to an overall reduction in the antioxidant level of body thereby increasing susceptibility to the disease. AMD is considered the leading cause of blindness in adults age 65 and over. However, AMD may be preventable. Evidence exists that indicates a strong association between adequate fruit and vegetable consumption and the reduced incidence of AMD and cataracts. Analysis of the National Health and Nutrition Examination Survey (NHANES I) shows a positive association between dietary antioxidants from fruits and vegetables with reduced risk and incidence of developing AMD. Similarly, it was also noted in the Eye Disease Case-Control Study that consumption of carotenoids-rich vegetables had a protective effect on the development of AMD, with spinach consumption showing the greatest AMD risk reduction. Researchers found that test subjects who had high levels of carotenoids in their blood, particularly lutein and zeaxanthin, were less likely to develop AMD.

In the Beaver Dam Eye Study, no positive correlation was found between lutein/zeaxanthin levels in the blood and AMD risk.35 However, other researchers have found that carotenoid-rich food intake does elevate carotenoid levels in the blood and can be used as a marker for fruit and vegetable intake. It has also been reported that test subjects given a diet with lutein and zeaxanthin–rich fruits and vegetables over 15 weeks showed an increase in blood lutein and zeaxanthin levels and also an increase in the overall density of the macula lutea, showing that the dietary intake of carotenoid-rich foods have an influence on eye health and may reduce the risk of AMD. For optimal protection from AMD, it has been suggested that proper maintenance of the macular pigment density comes from overall consistent consumption of carotenoid rich foods, rather than sporadic high dose supplementation. With cataracts, a disease that causes clouding of the eye lens with age and results in foggy vision necessitating extraction, it has been shown from the Nurse’s Health Study that individuals who consume diets rich in carotenoids (especially lutein and zeaxanthin) have a reduced risk of cataract extraction. Similarly in the Health Professionals Follow-Up Study, researchers found that therisk of cataract removal was reduced significantly when the diet included lutein and zeaxanthin-rich fruits and vegetables, particularly spinach and broccoli.

Lycopene

Lycopene is the red-orange color predominately found in tomatoes, but can also be found in watermelon, pink grapefruit, papaya, & guava. It is the most prevalent carotenoid found in the blood stream and is found in various organs such as the testicles, adrenal gland, liver, prostate, breast, pancreas, and skin. Lycopene is considered one of the most efficient singlet oxygen quenchers amongst the carotenoids. In human cancer cells, lycopene shows greater inhibition of cancer cell proliferation than and and b –carotene. It is speculated that lycopene may prevent coronary heart disease and cancer by inhibiting oxidation of LDL cholesterol, DNA, lipid membranes, and damaged oxidized molecular components by scavenging and neutralizing free radicals.

A recent review of the epidemiological evidence shows that there are statistically significant inverse relationships between the consumption of tomato-based foods (lycopene-rich) and reduced risk of prostate, lung, and stomach cancers. Inverse relationships (although not statistically significant) were also shown for cancers of the GI tract, breast, cervix, mouth, esophagus, and pancreas. Of the 72 studies reviewed, 57 showed inverse associations between tomato intake and site specific cancers (35 of which were statistically significant). However, 15 studies found no reduced risk or adverse effects. In the EURAMIC study, a lower risk of heart attack was found in subjects with higher lycopene storage in body fat.49 Lycopene may also help protect against oxidative stress from UV light in human skin by preferentially being destroyed prior to b –carotene. In a recent dietary intervention study, tomato-based food supplementation in human test subjects over a one-week period resulted in elevated blood serum lycopene and significantly reduced lipid peroxidation and LDL oxidation.

In terms of availability, Seis and Gartner and their co-workers found that lycopene was more bioavailable when tomato products were heat treated, mechanically processed, and consumed with oil than fresh tomatoes; possibly due to the increased breakdown of the lycopene-protein complex that allows lycopene to be released from the tissue.

Carotenoid-Based Natural Colors

A brief overview of the major carotenoid-based natural colorants have been summarized from current works and should be referenced for more detailed information.

Annatto

Annatto food color is derived from the seed coatings of the Bixa orellana bush that grows in the tropical regions of South America, India, Africa, & East Asia. It is one of the oldest colors used in history and has been used for coloring clothing, cosmetics, and food for centuries. The coloring principle of annatto comes from bixin, which is an oil soluble carotenoid, and imparts yellow-orange colors in many oil-based food applications. However, bixin can be saponified to obtain a water-soluble version of annatto color by forming norbixin. Annatto color comes in many forms (oil soluble, oil suspensions, water soluble, and powder) and can be stabilized for a variety of food applications. Annatto is the primary ingredient used to impart yellow-orange color in foods and is the main color for cheeses. However, annatto also is used in baked goods, savory applications, and meat casings. Stability to heat, light, and oxygen are generally good in complex food matrices that contain proteins and/or carbohydrates, but in water solution, they tend to have poor stability, limiting their application for beverages. Legally, annatto can be used in almost all parts of world. Bixin is considered a strong antioxidant and quencher of singlet oxygen and may help protect lipid membranes and inhibit lipid peroxidation.

Saffron & Gardenia

Saffron is ancient spice that has been used for both its color and flavor, but because of the high price of saffron, it primarily is sought after for its flavor. Saffron color comes from the dried stigmas of the Crocus sativus bulb that grows in the Mediterranean and parts of Europe. The color of saffron comes from the carotenoids, crocetin and crocin, which are generally water soluble and impart yellow-orange color to many types of food. These same carotenoids are also the, main coloring pigments found in Cape Jasmine (Gardenia jaminoids) but lack the flavor and high cost of saffron. These colors offer high color intensity and good stability to pH, light, heat, and oxygen. The application of saffron, however, is limited to gourmet food items because of its high cost. Gardenia color is currently not allowed in the United States but is allowed for use in other countries. Crocetin has been shown to possess antioxidant properties.

Paprika

Paprika color is made from ground sweet red pepper Capsicum annum and other red Capsicum species grown in warm climates such as India and the Mediterranean. Sought after for its flavor and spicy-heat, the color of paprika is derived mainly from capsanthin and capsorubin. Paprika colorants impart redorange color to many food products and are produced in powder or oil soluble oleoresin form. Because of paprika’s strong pungent flavor, its coloring applications are limited to tomato-based products, spices, dried meats, savory dried snacks, soups, and other savory types of applications. However, color manufacturers have developed water dispersible preparations and have attempted to reduce the flavor notes of paprika making it possible to color beverages and other water based food applications. Legally, paprika color can be used in most parts of the world including the EU and the USA.

Marigold

Marigold color is derived from Aztec Marigold (Tagetes erecta L.) grown in Central & North America, Spain and India. The coloring principle is derived primarily from lutein and other carotenoids and comes in powder and oleoresin preparations and imparts a yellow-orange color. In the United States, marigold color can only be used in animal feed for poultry and fish but in the EU, it has wide application in a variety of food applications including beverages, where stability is good to light, heat, and pH.

Fruits & Vegetables

Fruit and vegetable preparations have long been sources of natural carotenoid food color. Tomatoes, carrots, squashes and pumpkins are processed and concentrated for their color, yielding all-natural "foods having coloring properties" that can impart red, yellow, and orange color to both oil and water soluble food systems. In certain instances, preparations from fruits and vegetables are the only legal way to benefit from the coloring principle of certain carotenoids in food. Such is the case of tomato and the red-orange carotenoid, lycopene. In the United States, synthetic lycopene is not an approved colorant for food use; however, concentrated tomato juice color (which derives its color from lycopene) may be used in foods without legal barrier. Stability is generally good to light, heat, & pH.

Synthetic Carotenoids

With the discovery of carotenoids and the many useful colors they impart, many synthetic "nature identical" carotenoid colors have been developed for food coloring use, the most prevalent of which is b -carotene (yellow-orange).Lycopene (red-orange), lutein (yellow), canthaxanthin (orange-red), apo-8’-carotenal (yellow-red), and astaxanthin (red) colorants are commercially available as synthetic color preparations in powder and liquid formulations for oil or water-based food applications. Synthetics have similar stability to heat, light, pH, and oxygen, like other carotenoids, but because of their high concentration, the color preparations may need to be stabilized by reducing particle size, adding emulsifiers, or antioxidants, depending on the intended food application. -carotene is also used for its pro-vitamin A activity as well as coloring properties. Lycopene, lutein, and astaxanthin are not available for food use in the United States, however b -carotene, canthaxanthin, and apo-8’-carotenal, are permitted.