From http://www.sciencenews.org/articles/20040131/food.asp :
Bacteria Brew a B Vitamin Boost
When looking for naturally rich sources of cobalamin, better known as vitamin B12, most people turn to meats. Because the essential nutrient generally isn't present in plants, vegetarians run the risk of deficiency, which can cause neurological symptoms from tingling toes to disorientation and memory problems. Many of these people therefore turn to synthetic supplements or certain algal products rich in B12, such as tablets made from the blue-green Chlorella species.
However, anyone looking for a B12 boost might find an even more palatable source of the important vitamin in certain teas treated with bacteria, Japanese chemists now show. Various bacteria can make B12, and the researchers confirmed substantial quantities of the vitamin B12 in Batabata-cha, a so-called fermented black tea.
Unusual forms of Asian black tea, prepared using bacteria, can lace their brews with vitamin B12, making them some of the rare plant-based foods to offer this beneficial nutrient.
Most Western black teas, such as Darjeeling and Keemun, fall into a category known as self-oxidized. For these products, tea harvesters spread freshly picked leaves on wire screens so they'll wither, losing up to 70 percent of their moisture. The limp leaves then get passed under rollers. Tea enzymes released from cells within the leaves during the process begin what's termed auto-oxidation, in which oxygen-driven chemical processes transform the green leaves into brown "fermented" leaves over a period of 30 minutes to a few hours.
For some Asian black teas, however, processors enlist bacteria to control the oxidation. Knowing that the microbes can introduce various other compounds into tea leaves, Hiromi Kittaka-Katsura of Kyoto Women's University and her colleagues investigated whether B12 might be one of them. It's a member of a family of cobalt-based compounds known as corrinoids. Kittaka-Katsura's team had experience in such analyses, having recently confirmed the presence of B12 in Chlorella seaweed sold as tablets in Asian health food stores.
First the chemists brewed up some Batabata-cha. Then they used two different analytical techniques to confirm the presence of corrinoids in the liquid. When the scientists then ran the same tests on the type of B12 that's used in dietary supplements and enriched foods, cyano-B12, the results matched those for one of the tea's corrinoids. This confirmed that one of the tea products was indeed B12.
Reduces vitamin deficiency
To confirm that the body also recognizes the compound as B12, Kittaka-Katsura's group substituted the tea for the drinking water administered to young-adult rats for 6 weeks. These animals had been raised on a vitamin B12?deficient diet. Other B12-deficient rats instead received regular water or water laced with cyano-B12.
Urine tests confirmed that the rodents drinking tea became decreasingly vitamin-deficient. In fact, they improved more than the rats receiving B12 supplements. Animals getting regular water stayed vitamin-deficient throughout the test. The tea-drinking rats also grew more rapidly than all the other rats. Kittaka-Katsura's group concludes that the free form of B12 in the tea is absorbed more efficiently than the cyano-B12.
In fact, Kittaka-Katsura told Science News Online, her group's tests indicate that ordinarily, 70 percent of the tea's corrinoids exist as cyanocobalamin and the rest as methyl- or adenosyl-cobalamin - two forms of B12 that are more easily taken up and used by the body. However, she adds, because of the way her team prepared the tea for the animal-feeding trials, the cyano form was not present. The food scientist notes that this may explain why the tea's B12 outperformed the cyano form provided as a supplement to some of the other rats.
Drinking even a liter or two of the tea, depending on its brewed strength, would deliver only about 20 to 40 nanograms of B12, the researchers note„far too little to satisfy the recommended daily intake of about 2.4 micrograms. However, Kittaka-Katsura's team points out that it might be possible to create fermented-tea extracts as supplements more potent than such teas.
For now, she says her team is looking to confirm the tea's B12 potency in tests with people.
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Department of Food and Nutrition
Kyoto Women's University