The researchers found that the process of fermenting cabbage produces isothiocyanates, a class of compounds that have been identified in previous studies as potential cancer-fighting agents. In animal studies, the compounds appear to prevent the growth of cancer, particularly in the breast, colon, lung and liver, they say. No one knows yet whether the compounds, which are not found in raw cabbage, have a similar effect in humans. Further studies are needed, they add.
"We are finding that fermented cabbage could be healthier than raw or cooked cabbage, especially for fighting cancer," says Eeva-Liisa Ryhanen, Ph.D., research manager of MTT Agrifood Research Finland, located in Jokioinen, Finland. "We are now working on ways of optimizing the fermentation process to make it even healthier so that consumers will eat more [sauerkraut]."
In the current study, the researchers analyzed a variety of biologically active compounds in sauerkraut. Their samples were derived from white cabbage that was fermented.
Although raw cabbage is normally rich in a compound called glucosinolate, the researchers found that during the fermentation process enzymes are released that completely decompose the compound into several breakdown products. The majority of these products are cancer-fighting isothiocyanates.
Evidence for sauerkraut's anticancer effect is growing. Previous epidemiological studies have reported that Polish women who move to the United States have a higher incidence of breast cancer than those who remain in Poland, a statistic that some scientists attribute to a higher consumption of cabbage among the Polish women compared to their American counterparts.
At least one study found evidence that compounds in sauerkraut could inhibit estrogen, a hormone that can trigger the spread of breast cancer. The specific compounds have not been identified, however.
Currently, the researchers are investigating the effect of different starter cultures on the breakdown of glucosinolate. They hope the research may lead to sauerkraut with a greater abundance of healthy compounds, boosting its status as a functional (nutritious) food.
Besides anticancer compounds, the fermentation process also produces other healthy compounds not found in raw cabbage. These include organic acids such as lactic acid, which makes cabbage easier to digest. Although some loss in nutrients may occur during fermentation, sauerkraut is still a good source for vitamin C, certain minerals and dietary fiber, the researchers say.
Their work also adds to a growing number of studies demonstrating that similar cruciferous vegetables (including broccoli, cauliflower and Brussels sprouts) contain anticancer compounds.
Sauerkraut is a low-calorie, low-fat food that is second only to mustard as this country's favorite hot dog topping. Americans annually consume an estimated 387 million pounds of sauerkraut, or about 1.5 pounds per person yearly, according to Pickle Packers International, Inc., a trade association for the pickled vegetable industry.
Funding for this study was provided by Finland's Ministry of Agriculture and Forestry.
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