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Rooibos and Green Tea - Antioxidants are hot topics in the health news these days, and the herbal tea called rooibos (pronounced ROY-boss) is becoming popular because it is marketed as a healthy beverage with high levels of antioxidants.
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Rooibos: Botanical Description - Rooibos is a shrubby legume that is indigenous to the mountains of South Africa’s Western Cape.1-3 The genus Aspalathus includes more than 200 species native to South Africa.
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The type of A. linearis that is cultivated commercially for tea is the Red type, also known as the Rocklands type;1-6 native to the Pakhuis Pass in the northern Cedarberg region6 It grows erect, up to 1.5 m (about 5 feet) in height. It has a single basal stem that divides just above the ground surface into multiple thin branches that carry bright green, needle-like leaves of about 10—40 mm (0.4—1.6 inches) in length.7 The plant produces small yellow flowers in spring through early summer6, and each flower generates a one-seeded leguminous fruit.4,5. Rooibos has adapted to coarse, nutrient-poor, acidic soil and hot, dry summers.4,5,8 In addition to differences in morphology and genetics, researchers have found differences in chemistry between various populations of A. linearis.6,9 Van Wyk, of the Department of Botany at Rand Afrikaans University, presented results of his tests on the different wild populations of rooibos, showing significant variations in the polyphenol profile by population.9
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Rooibos: A Brief History - More than 300 years ago, indigenous inhabitants of the mountainous regions of South Africa’s Western Cape were the first to collect wild rooibos and use it to make tea.10
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These people discovered that they could brew a sweet, tasty tea from rooibos leaves and stems that they cut, bruised with wooden hammers, fermented in heaps, and then sun-dried. Botanists first recorded rooibos plants in 1772 when they were introduced to the tea by the Khoi people10. Rooibos became a cultivated crop by the early 1930s, has been grown commercially since World War II, and now is exported to countries worldwide, In 1999, about 29 percent of South Africa’s total rooibos sales were exported to 31 countries.10 The quantity of rooibos exported in 2000 was two and a half times greater than the quantity exported in 1999, and exports continue to grow10. Roughly 70 percent of the bulk rooibos that is exported goes through a partnership of private growers/processors and a cooperative of large and small farmers in the area. The rooibos is sold in a variety of products in Europe, Asia, and, increasingly, America. The Perishable Products Export Control Board (PPECB) of South Africa ensures that all exported rooibos products pass a phytosanitary inspection and are certified to be free of bacteria and impurities.4,10 In order to pass these health and safety tests, rooibos producers steam pasteurize the tea as the final step before packing. Organic rooibos is also monitored by various international organizations that provide organic certification, such as the German firms Ecocert and Lacon. Rutgers University in New Jersey provides a quality control program for ASNAPP’s Wupperthal tea program, evaluating parameters such as color, taste, aroma, pH, moisture content, cleanliness, total phenol content, and antioxidant capability for tea samples collected from the industry in general and from all the growers in the Wupperthal tea program.11 Data from their analyses are made available to the farmers and also to prospective buyers via product specification sheets.
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Click Table 5 |
Rooibos: Vitamins & Minerals - Despite some promotional claims that rooibos is a source of vitamin C, Joubert says it is not. "We have tested both the traditional rooibos and green rooibos, and vitamin C was not present," she says.22
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With the exceptions of fluoride and copper, the trace amounts of minerals in rooibos are not enough to make the tea a meaningful dietary source of minerals for the average consumer. As shown in Table 5, the nutritional labeling that is given on some packages of rooibos tea and on some websites of distributors4,5 indicates that the amounts of iron, potassium, zinc, calcium, and magnesium in a 200 ml serving of rooibos tea are all less than 1 percent of the U.S. reference daily intake (RDI). A 200 ml serving of rooibos provides over 5 percent of the RDI of fluoride for adults and over 7 percent of the RDI for copper ( see Table 5). Marc S. Micozzi, M.D., Ph.D., director of the Policy Institute for Integrative Medicine in Bethesda, Maryland, notes that when rooibos is used as a fluid replacement throughout the day, as is done with some athletes in South Africa, it does provide measurable amounts of several minerals and electrolytes.58
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Click Table 1 |
Antioxidants in Rooibos - Free radicals (unstable molecules with a lost an electron) can damage the DNA in cells, leading to cancer. They can oxidize cholesterol, leading to stroke, clogged blood vessels, heart attack.
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Antioxidants can bind to free radicals before the free radicals cause harm.Some antioxidants are called polyphenols because these substances contain a phenolic ring in their chemical structure. Polyphenols are common in plants; they act as pigments and sunscreens, as insect attractants and repellants, and as antimicrobials and antioxidants.12,13 The polyphenol group is further divided into subgroups such as flavonoids and phenolic acids. Polyphenols can also be classified as monomeric (molecules containing a single unit) or polymeric (larger molecules containing more than one unit). As described in this section, laboratory studies have found that rooibos tea contains polyphenol antioxidants, including flavonoids and phenolic acids, that are potent free radical scavengers.
Flavonoids: The polyphenol antioxidants identified in rooibos tea include the monomeric flavonoids aspalathin, nothofagin, quercetin, rutin, isoquercitrin, orientin, isoorientin, luteolin, vitexin, isovitexin, and chrysoeriol.14-19 Currently, rooibos is the only known natural source of aspalathin.15 Nothofagin is similar in structure to aspalathin and has only been identified in one other natural source besides rooibos: the heartwood of the red beech tree (Nothofagus fusca (Hook F.) Oerst, Nothofagaceae), which is native to New Zealand. 20
A recent analysis of fermented rooibos measured the levels of all the flavonoids listed above except nothofagin ( see Table 1).19 Of the 10 flavonoids measured, the three that occurred in largest amounts were aspalathin, rutin, and orientin, followed by isoorientin and isoquercitrin. Nothofagin was identified by mass spectrometry but was not quantified because a standard was not available. The amount of nothofagin in fermented and unfermented rooibos was estimated to be about three times less than aspalathin in one study.20 Aspalathin and nothofagin arepresent in relatively large amounts in unfermented rooibos tea,19,20 but some of the aspalathin and nothofagin oxidizes to other substancesduring fermentation; thus, fermented rooibos contains less aspalathin and nothofagin than unfermented rooibos. 20 The change in polyphenol composition is the reason the tea changes color with fermentation.20
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Phenolic Acids - Rooibos also contains phenolic acids that have been shown to have antioxidant activity.14,18,21 Like flavonoids, phenolic acids are polyphenol substances that are found in fruits, vegetables, and whole grains.
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The phenolic acids identified in rooibos tea, in decreasing order of antioxidant activity as measured in one study21 with the commonly used 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay, include caffeic acid, protocatechuic acid, syringic acid, ferulic acid, vanillic acid, p-hydroxybenzoic acid, and p-coumaric acid.14,18 Using the DPPH assay, caffeic acid was just as active an antioxidant as the most potent flavonoids tested (quercetin, isoquercitrin, and aspalathin).21
Total Polyphenol Content: Despite some promotional claims, a serving of rooibos tea has less total polyphenols than the same size serving of green or black tea. Serving size varies, but for comparison purposes a 150 to 200 ml serving is often used (about 3/4 of a standard baking measuring cup). Elizabeth Joubert, Ph.D., specialist researcher at South Africa’s ARC Infruitec-Nietvoorbij and a rooibos expert, says that the total polyphenol content of an average 150 to 200 ml serving of rooibos tea can be as much as 60 to 80 mg, depending on factors such as the brewing time and amount of leaves used.22 For comparison, one study found that brewing black tea leaves for 1 to 3 minutes at a concentration of 1 g leaves per 100 ml water resulted in black tea that contains 128 to 199 mg of polyphenols per 200 ml serving of tea.23 The types of polyphenols in rooibos tea are different than those in green and black teas, so the potential health benefits of the teas cannot be compared solely on their total polyphenol content. Rooibos tea does not contain epigallocatechin gallate (EGCG), which is a polyphenol in green tea that has shown anticarcinogenic and antioxidant capabilities, but many of the polyphenols in rooibos tea are also strong antioxidants.
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Quercetin and Luteolin - Two flavonoids in rooibos tea, quercetin and luteolin, are potent antioxidants. Test tube studies demonstrate these antioxidants can cause cancer cells to "commit suicide," (Apoptosis).24-27
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Quercetin decreased primary tumor growth and prevented metastasis in a model of pancreatic cancer.25 Luteolin and quercetin inhibited proliferation of thyroid28 and colon29 cancer cells, respectively, in vitro. Quercetin inhibited cyclooxygenase-2 (COX-2) expression in colon cancer cells, which may help prevent colon cancer.30,31 Both luteolin and quercetin can block the formation of lipid peroxides.32-34
Although studies like these show quercetin and luteolin are strong antioxidants, researchers haven’t yet determined whether enough of either of these two flavonoids are present in rooibos tea and absorbed by the body to have beneficial effects. As shown in Table 1, recent analysis of fermented rooibos found considerably more quercetin than luteolin,19 but even quercetin was present in much lower amounts than aspalathin, orientin, and rutin.
Based on the data in Table 1, a 150 ml serving of fermented rooibos tea made with 2.5 g of tea leaves has about 0.27 mg of quercetin; for comparison, one study found that C. sinensis contains 1.5 to 3.75 mg of quercetin per 150 ml serving of tea.35 A previous study36 found 1.5 mg of quercetin per 150 ml serving of fermented rooibos, but that may be an upper limit. Joubert says that the 1.5 mg estimate is probably high,22 but emphasizes that these estimates will vary with parameters such as the brewing time and the amount of water and tea leaves used. At any rate, the amount of quercetin per serving of rooibos is a small percentage of the total polyphenol content per serving of rooibos.
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