Phytochemicals: Beyond Vitamins and Minerals

Phytochemicals:
Beyond Vitamins and Minerals
July 1999 -- Cover Story

By: Christine Homsey
Contributing Editor

  A respected Des Moines pharmacist for some forty years, my grandfather felt there was no ill that a pill couldn't fix. Got a headache? Take some Tylenol®. Have a cold? Here's the Chlor-Trimeton®. And oh - don't forget to take your vitamins, too. Although most Americans subscribed to Grandpa's very Western view of medicine for decades, consumers now also look to food for prevention of illness, rather than solely to drugs for a cure. Phytochemicals in fruits, vegetables and legumes are now gaining attention as a means of preventing myriad mental and physical ailments.

Phyto facts

  What precisely is a phytochemical? Tracing its Greek roots, the word literally means "plant chemical." This simple definition would indicate that any chemical (even water) produced by a plant would be referred to as a phytochemical. But, says Patricia Murphy, Ph.D., professor of food science and human nutrition at Iowa State University, Ames, "the word phytochemical is currently being used to identify the chemical constituents of plants that are not in the usual class of proteins, fats, carbohydrates, vitamins and minerals used as part of our nutritional requirements. Phytochemicals are all the other constituents that may or may not have health-related effects, both positive and negative."

  Many potential health benefits and functions of phytochemicals have not yet been recognized; in fact, some of the compounds themselves have not been identified. There's a frenzy of epidemiological, animal and human studies, however, and promising results indicate that specific phytochemicals may prevent chronic diseases (including cancer), help manage symptoms of chronic disorders, improve immune response, and even minimize negative effects of aging.

  Although some of the preliminary results are exciting, information on certain substances is extremely limited, inconclusive or contradictory. In their haste to rush new functional food products to market, some companies overlook the lack of evidence for efficacy of these compounds. Before adding phytochemicals to a food, manufacturers should study the available research, be aware of any federal regulations and recommended doses, and assess whether benefits outweigh any risks. At the very least, added ingredients should do no harm.

  Researchers are just beginning to quantify phytochemical content of specific ingredients - something of a challenge, since these compounds can vary within a given food. Says Murphy: "In my own experience with soy isoflavones, we observe that the levels in soybeans, even from the same field grown all in the same year, may vary in concentration by a factor of five. I would expect other plants to be similar and wild plants to have even greater variability."

  Whether plunging headfirst into the nutraceutical market or adopting a wait-and-see attitude, staying abreast of the latest phytochemical news is recommended, as functional foods are sure to become bigger business. Plants contain thousands of chemicals - keeping track of all of them is difficult; but some of the more talked-about and well-researched compounds include: phytoestrogens (isoflavones, resveratrol, lignans); carotenoids (lycopene, beta-carotene, lutein, zeaxanthin); anthocyanins; polyphenols (catechins, oligomeric proanthocyanidins); and sulfur compounds (allicin, isothiocyanates, indoles). Although not covered in detail here, some other plant-derived products to keep an eye on include omega-3 polyunsaturated fatty acids, limonoids, saponins and stanol esters.

Fabulous phytoestrogens

  Certain phytochemicals are classified as phytoestrogens, or pseudoestrogens, because they bind to receptors in the body much as human estrogen does. Compounds currently classified as phytoestrogens include isoflavones found in soy products, resveratrol in grapes, and hydrolysis products of lignans in flaxseed. Although the estrogenic activity of these plant-based compounds is relatively weak, they can reach much higher levels in the blood than human estrogen, resulting in a similar biological net effect.

  Soy isoflavones. Soybeans have been an important, protein-rich source of food to humans for 5,000 years, but only recently have they begun to receive full credit for their functional and nutritional properties. Approximately four decades ago, processors began concentrating soy protein to create a variety of functional ingredients, and in the 1990s, soy products have garnered publicity as a result of their high isoflavone content.

  Isoflavones, associated with the protein fraction of soybeans, have been credited with alleviating menopausal symptoms and slowing or reversing bone degeneration (osteoporosis). Interview studies show that women who consume 40 grams of soy protein daily have increases in bone density.

  Because estrogen helps manage hot flashes and other symptoms of menopause for many women, it follows that phytoestrogens would have some benefit as well. Whether isoflavones prevent or promote estrogen-related diseases such as breast cancer is still unclear. "They may act as promoters as natural estrogens do, or they may act as anti-estrogens and just block out the ability of natural estrogen to promote estrogen-dependent cancers," notes Murphy. "The evidence is not fully in." She says that another unknown is whether isoflavones interfere with prescription drugs or hormone replacement therapies that are commonly prescribed for menopausal women.

  The most-studied isoflavones are genistein, daidzein and glycitein. Of these, genistein has been the most widely researched. These compounds are found in glycoside (with a sugar molecule attached) or aglycone (no sugar) form. Whether the molecule is in glycoside or aglycone form has no impact on bioavailability, although glycitein is more bioavailable than daidzein, which in turn is more bioavailable than genistein.

  Soy products come in a wide variety of flavors, textures, and forms: soymilk; soy flour, concentrates and isolates; tofu; and fermented products such as miso and tempeh. These high-protein ingredients can be turned into faux hotdogs and burgers, ground-beef-like crumbles, yogurt, cheese, frozen desserts and beverages. Most recently, isoflavone concentrates have been developed for atypical applications that require minimal functional or flavor impact.

  Soymilk can substitute for cow's milk in several applications, such as baked goods and frozen desserts. In most cases, direct replacement of cow's milk with soymilk yields good results, although fine-tuning may be needed. For instance, when using soymilk in baked goods, texture and degree of browning may differ from that yielded by dairy products, because of differences in sugar and protein make-up. Therefore, baking and other processing procedures might need adjustments. Flavor work might be required to compensate for lost dairy notes or to mask any detectable soy character.

  Although soymilk has traditionally been described as grassy or beany, many newer products have a bland flavor, making them suitable for a wide variety of foods and beverages. Consider, however, that the more grassy and beany the flavor, the higher the isoflavone levels, which result from sugars that remain in the soymilk during processing.

  According to Steve Buchheim, marketing manager at Archer Daniels Midland in Decatur, IL, soy proteins are available in three basic forms: soy flour, soy concentrate flour, and isolated soy protein. Soy flour and soy concentrate flour can be textured to create, respectively, textured vegetable protein (TVP) and textured soy concentrate (TSC). To make soy flour, processors remove the soybean's outer shell and oil, resulting in a product with about 50% protein. When this process is taken a step further, the sugars are removed, resulting in soy concentrate that is 70% protein. When taken further yet, the fiber is removed, creating a 90% protein product known as isolated soy protein.

  Soy flour and soy concentrate flour are utilized in cookies, cakes, fortified cereals, ground meats and sausages, and in any other products where their viscosifying, emulsifying, binding and nutritional properties are a plus. TVP and TSC can form meat analogs, especially in no-cholesterol, reduced-fat or vegetarian applications.

  These soy products contain varying levels of isoflavones, depending on their origin and the protein-concentration method, although soy flour usually retains more isoflavones than soy concentrate. Isoflavone content in soy concentrate depends on whether it has been water-washed or alcohol-washed, as isoflavones are soluble in alcohol. Because of its blander flavor, soy concentrate is often preferred over soy flour. Processing removes most of a concentrate's sugars, which cause the grassy, beany notes in some soy products.

  Soy isolates, the most concentrated form of soy protein available, generally contain about half as many isoflavones as soy flour as a result of losses during processing. Functionally, isolated soy protein has many of the same attributes as soy flour and concentrates, and is used in whole-muscle meats, hotdogs, pastas, cereals, health bars and powdered nutritional beverages. Soy isolate is available in many forms, including some that are very bland in flavor. Solubility is variable, and counterintuitively, some of the more soluble forms can cause graininess in fluid products.

  Isoflavone concentrates are a more recent development, and according to Laurent Leduc, international marketing manager for Minneapolis-based Schouten USA Inc., offer a means to adjust isoflavone levels in foods, with minimal functional impact. These concentrates are available in several forms for various applications; for example, a dry drink mix would use a very fine granulation. Because the solubility of some isoflavone concentrates is limited, more-soluble forms are being developed for clear and ready-to-drink beverages.

  Isoflavone concentrates can have roasted-nut aromas and flavors, but due to their low usage levels, no off-flavors are usually detected in the finished product.

  The decision to label a product as a food or a supplement will impact which isoflavone concentrate is suitable for use. For example, Schouten markets a 3% isoflavone concentrate that is generally recognized as safe (GRAS) and can be used in conventional food products, but the company's 10% concentrate is considered a dietary supplement. Two to three grams of a 3% concentrate deliver about 50 to 90 mg of isoflavones, approximately the same daily level used in many medical studies, and the amount found in a traditional Japanese diet.

  Regardless of the soy ingredient used, always check the isoflavone level with the supplier if the product is to be sold for its phytochemical benefits. Also, when calculating the relative potencies of various soy products, consider whether the isoflavones are in glycoside or aglycone form. Isoflavones are very heat-stable, making them suitable for high-temperature processes.

  Soy's beneficial components are not just limited to isoflavones. Many potential anticarcinogens have been identified in soybeans, such as saponins, phenolic acids, phytic acid, protease inhibitors and phytosterols. The protein itself may have protective effects. Evidence indicating that soy protein reduces the risk of coronary heart disease (CHD) has convinced the FDA to consider allowing a new health claim. Labels on food products containing a minimum of 6.25 grams of soy protein per serving would be allowed to explain the positive impact of soy on risk of CHD when used as part of a low-saturated-fat, low-cholesterol diet. This benefit may be strictly associated with the protein itself, as studies have shown that isoflavones alone do not lower cholesterol levels in humans.

  Resveratrol, a phenolic compound thought to have estrogenic effects, is found at high levels in purple grapes, grape juice, red wine and peanuts. In addition to being described as a phytoestrogen, resveratrol has been associated with decreased risk of CHD. Resveratrol is thought to lower risk of CHD by many mechanisms, including reduced aggregation ("stickiness") of blood platelets, increased high-density lipoprotein (HDL, or "good") cholesterol, and various antioxidant mechanisms.

  When red grapes are processed into juice or wine, the skins are included in the initial fermentation process to give the beverage its color. Resveratrol also seeps out of the skins during this operation. White wine and white grape juice have a much lower resveratrol content because the skins are removed during processing. Although the grape variety and processing affect resveratrol content, a 5-oz. glass of red wine contains about 800 mg, according to the USDA Agricultural Research Service. Peanuts are also a significant source of resveratrol, at about 73 mg per oz., and resveratrol supplements have recently entered the marketplace.

  Lignans, found in flaxseed and sesame oils, are converted to estrogen-like substances by bacteria in the colon. Enterodiol and its oxidation product, enterolactone, are formed in the intestinal tracts of mammals from lignan precursors. Like soy isoflavones, these pseudoestrogens can bind to estrogen receptors, and might inhibit growth of breast tumors and other estrogen-stimulated cancers. As with isoflavones, this hypothesis has not yet been entirely supported. Flaxseed has been shown to decrease colon and mammary gland tumors in rodents, however.

  Although not traditionally considered a food ingredient in North America, flaxseed is the richest known source of mammalian lignan precursors. Flaxseed consumption has been shown to lower both total and low-density lipoprotein (LDL, or "bad") cholesterols and to reduce platelet aggregation. Flaxseed extracts and purified lignans both exhibit antioxidant effects, and might therefore act as antimutagens and anticarcinogens.

  Whole or ground flaxseed is now being including in cereals, health bars, tortilla chips, breads and other baked goods. Flax flour and flax meal are available as well. Although not yet commercially available, processors are developing methods for the production of flaxseed protein concentrate and flaxseed protein isolate.

  After oil has been pressed from flaxseed, no lignans remain in the oil. Flaxseed oil is worthy of note, however, because it contains the highest level of alpha-linoleic acid of all seed oils. This fatty acid is an omega-3 fatty acid. Omega-3s in flaxseed, canola oil and walnuts have anti-inflammatory properties, and have been associated with reduced risk of heart disease. The high-lignan flaxseed oils that are now available have had lignans added back after the processing.

  Although commonly used as a basis for paints, flaxseed (or linseed) oil has had limited utility in the food industry because of its proclivity to oxidative rancidity, polymerization and off-flavors. Grocery stores currently sell filtered flaxseed oil, packed in light-impermeable containers in which an inert gas such as argon has been used to flush the head space of oxygen.

  Flaxseed oil is not recommended for frying because of its instability at even slightly elevated temperatures, but it has found some use in cold-processed salad dressings. Unopened, a container of flaxseed oil will last about six months from the date of extraction. Opened, its quality dwindles quickly in about six to eight weeks.

  Flaxseed and flaxseed oil are not GRAS. According to Barry Hall, marketing director of the Flax Council of Canada, Winnipeg, Manitoba, they were overlooked when other ingredients were grandfathered onto the GRAS list because flax was not considered a common food ingredient in North America. Hall says that the FDA has not objected to a usage level of 10% to 12% whole flaxseed, however.

Calling all carotenoids

  The 4000 known pigments that lend beautiful colors to fruits and vegetables not only enhance the pleasure of our eating experiences, but offer protective health benefits as well. Carotenoids are one such group of pigments and includes the antioxidants lycopene, beta-carotene, lutein and zeaxanthin. These compounds may impede tumors and enhance human immune systems. Some carotenoids, such as beta-carotene and lycopene, protect against UV radiation.

  Carotenoids are yellow to red in color, giving many fruits and vegetables their characteristic color. They also occur in green vegetables, where they are masked by the presence of chlorophyll. Good sources of carotenoids include yellow-orange vegetables (carrots, pumpkins, and sweet potatoes), leafy/green vegetables (kale, collard greens, spinach, and broccoli), and red or yellow-orange fruits (tomatoes, strawberries, watermelon, cantaloupe, mangoes, pineapples, and peaches).

  Carotenoids are fat-soluble, but some commercially prepared forms can be water-dispersible as well. Carotenoids are sensitive to oxygen, light, extreme pHs, and prolonged heat (especially over 113°F). Therefore, the concentrated nutrient forms should be stored in cool areas in packaging that does not permit oxygen or light to pass through. When incorporating these ingredients into products, overage amounts might be necessary to compensate for processing and storage losses, anywhere from 10% to 100% depending on the type of processing and heat treatment used.

  Lycopene has been found to be the most effective quencher of singlet oxygen in living systems, thus making it a potent antioxidant. This mechanism is thought to be responsible for lycopene's potential ability to reduce the risk of heart attacks and prostate cancer. Some other cancers whose risks seem to be reduced with lycopene are lung, breast, bladder, cervical and skin. Lycopene has also been linked to reductions in cancers of the digestive tract, including the mouth, pharynx, esophagus, stomach, colon and rectum. However, direct cause-and-effect relationships have yet to be proven in properly conducted clinical intervention trials.

  According to the latest research, processed tomato products are the best source of lycopene, but pink grapefruit, watermelon, peaches, apricots, eggplant, papaya and pink guava contain lower levels. That red fruits provide lycopene does not come as a surprise, since it is the pigment that gives them their red color. As one might expect, the degree of redness of these fruits can indicate the level of lycopene present, although not all red plant products contain this carotenoid.

  Although many nutrients found in produce suffer from processing, lycopene is not one of them. Tomato sauce, tomato paste, canned tomatoes, ketchup and some concentrated vegetable juices all contain beneficial levels. Although one fresh tomato provides about 10 mg of lycopene, it is in the form of crystals that are physically bound within the cell structure. When tomatoes are heated, their fiber is broken down and lycopene is released from the cellular matrix, making it more easily absorbed in the human digestive tract.

  About 85% to 90% of most people's daily intake of lycopene comes in the form of tomatoes, so including processed tomato products in a formulation is an easy way to help consumers reap its benefits. Obvious applications would include pasta sauces, soups and pizzas. Because lycopene is fat-soluble, including a small amount of fat in a formulation can help increase its bioavailability.

  Putting tomato ingredients in wet systems where tomato color, flavor and texture are desirable is generally not a problem, but dry systems might be another story. For instance, including tomato powder in a low-moisture cracker can be a challenge because of its attendant hygroscopicity. For a product in which tomato character is not appropriate, concentrated forms are available as individual ingredients or as part of nutrient blends.

  Beta-carotene has been included in vitamin and mineral supplements for many years, and is thus one of the most recognized carotenoids. Carrots, melons and sweet potatoes are good sources. Beta-carotene is unique in that it is one of the relatively few precursor molecules from which the human body can synthesize vitamin A.

  Because beta-carotene has long been believed to have antioxidant properties that prevent cancer, new produce varieties have been developed that contain elevated levels of this nutrient. A maroon-colored carrot called Betasweet has been developed by plant breeders at Texas A&M University, College Station, TX, with 25% to 35% more beta-carotene than regular commercial varieties.

  Although its benefits are many, beta-carotene has been found to be harmful in a few instances, underscoring how much more we have to learn about phytochemicals in general. For example, studies show high-dose beta-carotene supplements increase the risk of lung cancer in smokers, although no reports of permanent harmful effects of this nutrient when consumed in foods have surfaced. These effects were likely a result of the fact that natural forms of beta-carotene are much less bioavailable than synthetic forms. Some studies based dosages on the beta-carotene content of diets rich in fruits and vegetables, but used synthetic forms in the actual trial. Deleterious effects may be observed when doses of the synthetic form reach about 30 mg a day, but generally, 6 to 10 mg per day is considered safe whether in food or supplement form.

  As with lycopene and other carotenoids, beta-carotene is fat-soluble, so including a bit of fat in a formulation may help increase absorption through the intestinal wall. Beta-carotene is GRAS and has found substantial use as a colorant, ranging in hue from yellow to orange.

  Dry, cold-water-dispersible forms are available in 10%, 7% or 1% versions. In beverages, optimum stability can be achieved by first dissolving the powder in distilled water to make a stock solution, then adding it to the beverage to achieve the desired color. A stable emulsion prevents "ringing" of the color at the top of the beverage. When formulating powdered drink mixes, you may simply blend the beta-carotene powder with the other ingredients. For use in a lipid phase, 30% beta-carotene is available suspended in vegetable oil. Some insoluble, colorless forms are also available when just a nutritional benefit is desired. Potential targets for fortification with beta-carotene include breakfast cereals, snack bars, beverages and dairy products that are not governed by standards of identity (such as smoothies).

  Lutein and zeaxanthin are now sold as supplements, and are being included in nutrient blends. These carotenoids might reduce risk of age-related macular degeneration (AMD), which is caused by irreversible deterioration of the macula lutea, the yellow spot in the retina of the eye. Interestingly, the macula actually contains lutein and zeaxanthin, which are responsible for the macula's yellow color. AMD, a leading cause of blindness in Western nations, has no cure and few treatment options, so prevention is crucial.

  Dark, leafy green vegetables, especially spinach and kale, are excellent sources of lutein and zeaxanthin. Levels of these substances may be increased through either produce or supplements, but dosages are uncertain because of limited research. Although yellow in hue, isolated forms of these carotenoids are not likely to gain wide acceptance as colorants because of their high cost.

Anthocyanin action

  Another group of antioxidant pigments is the anthocyanins, the water-soluble, reddish compounds found in many intensely colored fruits such as strawberries, cherries, cranberries, raspberries, blueberries, red grapes and black currants. In addition to possessing cancer-preventative properties, anthocyanins in red grapes might provide protection from heart disease by limiting cholesterol synthesis or reducing stickiness of blood platelets.

  You may have noticed that some of the health benefits ascribed to anthocyanins are the same as those attributed to resveratrol and oligomeric proanthocyanidins in grape products; researchers are not certain exactly which compounds are responsible for these effects or whether they are synergistic. To complicate matters further, grapes also contain flavonoids such as quercetin and myricetin, which are being investigated as potential anticarcinogens as well.

  The color of grapes and grape products depends on the mix and sheer quantity of anthocyanins they contain. The exact hue that an anthocyanin-containing ingredient will impart depends on the food system's pH. In general, the lower the pH, the more vibrant the red. A pH range of 4.5 to 7.0 will cause anthocyanins to be much lighter in color, and basic pHs may result in yellow tones.

  Grape-skin extracts are very vivid purple or red water-soluble concentrates or powders that can be used to color beverages in accordance with 21 CFR section 73.170. Anthocyanin content depends on the grape source and manufacturer's process. Some grape skin extracts contain high quantities of sulfur dioxide (SO2), which is used as a solvent to aid in extraction of anthocyanins, and may be a concern for those with allergies to SO2. Non-SO2 containing forms are available with various anthocyanin levels, although different processes are used to extract them. Grape-juice concentrates present another option for adding these phytochemicals to products.

Pick a polyphenol

  Grape-seed extract, pine-bark extract and green tea are currently being studied for their polyphenols, compounds that appear to protect against various cancers in animal studies. The building blocks of these polyphenols are common to green tea, grape seeds and pine-bark extract, although the building blocks occur in different combinations.

  Oligomeric proanthocyanidins, or OPCs, are water-soluble, condensed tannins found in red wine, grape seeds and pine bark. In addition to their own antioxidant ability, OPCs have been found to spare other antioxidants such as vitamins C and E. Antioxidants such as OPCs might slow the aging process and arrest cancer cells because they inhibit oxidants and free radicals that damage cells and tissue. They also strengthen blood vessels and reduce platelet aggregation, and may thus prevent circulatory problems.

  The negative correlation between heart disease and red wine consumption was found when it was discovered that, despite high intakes of saturated fat and dietary cholesterol, France has relatively low rates of heart disease. This phenomenon became known as the "French paradox," which is thought to be a result of protective phytochemicals in red wine. Because red wines are in contact longer with the seeds during fermentation, they contain much higher levels of OPCs than white wines.

  Not every consumer can, or wants, to consume a large amount of phytochemicals via red wine, so concentrated OPCs offer an alternative. OPC concentrates such as grape-seed and pine-bark extracts are not yet GRAS or considered as food additives, and can therefore only be used in "food-like" items or other products labeled as dietary supplements.

  Suggested daily intakes of OPCs vary widely, depending on whether the dose is intended to be preventative or therapeutic. Many manufacturers of grape-seed extract supplements use about 25 or 50 mg per tablet or capsule. Grape-seed extract has been used less commonly in the United States than in Europe, where it has been prescribed for a variety of ailments such as high blood pressure, cardiovascular damage, weakened blood vessels and fluid retention.

  JoLynne Wightman, Ph.D., research chemist for Canandaigua Wine Company in Madera, CA, says that there is no agreed-upon method to determine OPC content in grape-seed or pine-bark extracts. The potency of some of these extracts is measured only on total phenol content, so total OPC levels and composition may not be declared. Manufacturers of grape-seed extract are currently working to standardize analytical procedures across the industry.

  Grape-seed extract is generally sold in powder or granular form, although it can also be sold as an alcohol tincture. Polyphenolics, a subsidiary of Canandaigua Brands located in Burlingame, CA, markets a water-soluble, powdered grape-seed extract produced from unfermented seeds. This orange-rose powder is sold under the name Vinox™. These extracts are very soluble in water and, according to Wightman, have minimal loss of phenols when boiled at atmospheric pressures for up to one hour. On its own, grape-seed extract is generally astringent in flavor because of its tannin content.

  An extract marketed by Henkel Corporation's Nutrition and Health Group, LaGrange, IL, under the trade name Pycnogenol®, contains the same water-soluble OPCs found in grape seed, but its source is the bark of the French maritime pine tree.

Catch a catechin

  On a dry-matter basis, polyphenols make up about 30% of fresh tea leaves. Catechins are the primary phenolic compounds found in tea, and the four major catechins in green tea are epigallocatechin-3-gallate, epigallocatechin, epicatechin-3-gallate and epicatechin. Says Clare Hasler, Ph.D., executive director of the Functional Foods for Health Program at the University of Illinois, Urbana-Champaign: "Tea is very unique in that it has very specific polyphenolic compounds that you don't find in other foods, the catechins in particular. The epidemiological studies, however, do not show a protective effect like the animal studies. More clinical trials are needed with tea consumption and looking at biomarkers of cancer risk reduction, but the problem is that we do not have agreed-upon biomarkers."

  Catechins are the tannins responsible for tea's astringency, and green tea contains high concentrations. When green tea is fermented into black tea, the catechin content diminishes. Green-tea extracts are available in both powder and liquid form, but one of the main challenges to using them is their bitter flavor. Cloudiness can also cause problems when formulating a transparent beverage. So far, the main applications for these extracts have been beverages, tablets, capsules and some nutrition bars.

  Although most studies on green tea have focused on its catechin content and cancer preventative properties, some preliminary evidence shows that tea flavonoids such as quercetin, kaempferol, myricetin, apigenin and luteolin may reduce the risk of heart disease. Grape-seed and grape-skin extract also contain catechins; grapes contain catechin, epicatechin and epicatechin gallate.

All for alliums

  Garlic (Allium sativum) contains many water- and oil-soluble sulfur compounds that researchers are closely examining. Currently, they are unsure as to the specific chemicals that confer protective effects, but much research has centered on the compound allicin. When cloves of garlic are crushed, the enzyme allinase converts alliin (an odorless amino acid) into allicin (which gives garlic its typical aroma). Allicin then decomposes to produce several other sulfur compounds.

  Most forms of garlic intended for use in conventional foods are not standardized for allicin content, although a few companies use allicin, alliin and total sulfur as marker compounds. Some dried forms have been selected and processed to control the allicin reaction, but because of the high cost of the process, these ingredients are primarily sold to manufacturers of dietary supplements. Garlic in its whole form is thought to have the most benefits because of synergies among its constituents. Some types of processed garlic, such as aged garlic extract, are high in allicin-related compounds called ajoenes, and are being sold as dietary supplements.

  Thanks to the popularity of heavily flavored Italian and Asian cuisines, as well as interest in natural remedies, garlic has enjoyed a surge in sales and is the second most popular herb in the United States. Not only is this odorous bulb improving processors' profit-and-loss statements, but it may keep us healthy as well. One-half to one clove of garlic per day has been found to lower high cholesterol in several clinical trials, and garlic might also prevent cancer, lower blood pressure and act as an antibiotic. Some of the preliminary research has been inconclusive, however, due in part to the variations in potency and form of the garlic used in studies.

  Garlic's strong flavor might be off-putting in some applications. Strategic flavor-masking might be in order; some ingredients that can help camouflage or neutralize garlic odors are vanilla, mint and parsley.

  Although much of the research on the health benefits of alliums has focused on garlic, researchers at Texas A&M are developing an onion containing elevated levels of quercetin, which might prevent stomach cancer.

Get your glycosides

  Anticarcinogenic properties have also been ascribed to glucosinolates, a group of glycosides found in all cruciferous vegetables (e.g., cabbage, broccoli, cauliflower, Brussels sprouts). Enzymes convert these substances into a variety of compounds such as isothiocyanates and indoles. One isothiocyanate in particular, sulforaphane, has been isolated from broccoli, and its precursor occurs in high levels in broccoli sprouts. Similarly, a specific indole, indole-3 carbinol, is under study for a possible role in reducing risk of cancer of the mammary gland, although it is unclear at this time whether it inhibits or actually promotes cancer.

  One thing that is clear, however, is that many of our old notions about nutrition, medicine and healthful lifestyles are being revised, and that phytochemicals will continue to play a large role in future developments. Perhaps instead of focusing only on prescriptions and vitamin C, we will begin striving to get our daily doses of isoflavones, indoles and isothiocyanates, as well as the numerous other compounds in the phytochemical category.

Approximate Isoflavone Content of Soyfoods and Soy Products*

*Total isoflavones expressed as aglycone units. Note that
isoflavone content can vary considerably among brands and
that the isoflavone content of soybeans varies among cultivars
and is affected by environmental conditions.

Courtesy of Archer Daniels Midland, Decatur, IL

  Christine M. Homsey is a food scientist with the consulting firm of Food Perspectives in Plymouth, MN. She has developed products for the grocery and restaurant industries and is pursuing a graduate degree at the University of Minnesota. An admitted "junkatarian," Chris is still struggling to eat her five-a-day fruits and veggies.

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