The polyphenols in tea may preferentially suppress the growth of pathogenic bacteria in the gut, but not the growth of “friendly” bacteria, says a new study from Singapore.
“It is generally believed that possible beneficial health effects of tea polyphenols are due to their antioxidant activity,” wrote lead author Hui Cheng Lee from the National University of Singapore. “Evidence from our study indicates that phenolics are likely to benefit the host by inhibiting pathogen growth and regulating commensal [normal] bacteria, including probiotics, and could therefore be considered as prebiotics.” [Probiotics are bacteria beneficial for healthy intestinal function, and prebiotics promote the growth of probiotics.]
The health benefits of tea - ranging from a lower risk of certain cancers to weight loss, and protection against Alzheimer's - have been linked to the polyphenol content of the tea.
n Green tea contains between 30 and 40 percent water-extractable polyphenols,
n While black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 percent,
n And Oolong tea is semi-fermented tea, and is somewhere between green and black tea.
The four primary polyphenols found in fresh tea leaves are epigallocatechin gallate (EGCG), epigallocatechin, epicatechin gallate, and epicatechin.
The new study, published in the [November 2006 issue of] the journal Research in Microbiology**, looked at the effects of 31 different phenolics extracted from Yunnan Chinese tea on the growth of 28 different bacteria, including pathogenic, commensal (normal), and probiotics found in the intestine. These included:
n Strains of the aerobic pathogens E. coli, Salmonella, and Listeria,
n Probiotic Lactobacillus strains,
n Strains of the anaerobic pathogens Bacteroides and Clostridium,
n And probiotic Bifidobacterium strains.
Cells were cultured in the presence of 0.1 percent polyphenols at 37 degrees Celsius for 24 hours.
“Our data demonstrate that phenolic compounds have general inhibitory effects on intestinal bacteria. The level of inhibition varies depending on the bacterial species and chemical structure of the compound,” wrote Lee.
Indeed, growth of the pathogenic E. coli and Salmonella typhimurium were most strongly inhibited by the tea polyphenols and their metabolites, as were strains belonging to the pathogenic Bacteroides and Clostridium genera.
However, the researchers report that the growth of the probiotic Bifidobacterium and Lactobacillus strains were less affected by the tea compounds.
“Since probiotic growth was relatively unaffected by most of the aromatic compounds tested, probiotic colonization in the intestine should continue in the presence of phenolics so as to improve the intestinal microbial balance and inhibit pathogen growth,” said the researchers. And, “although not fully comprehensive, this in vitro study indicates a substantial number of complex interactions between intestinal bacteria, phenolics, and their metabolism,” they said.
They called for more research to further investigate the influence of the tea polyphenols on gut microflora, and the overall maintenance of human health and disease prevention, and said that the research suggests that the antioxidants may also be prebiotic....
* This article is reproduced with permission of DecisionNewsMedia www.decisionnewsmedia.com, which published it online December 20, 2006. Copyright 2006 DecisionNewsMedia.
** “Effect of tea phenolics and their aromatic fecal bacterial metabolites on intestinal microbiota,” by H.C. Lee, A.M. Jenner, C.S. Low, and Y. K. Lee. Published in the November 2006 issue of the journal Research in Microbiology, volume 157, issue 9, pages 876-884. The researchers are affiliated with the Departments of Microbiology and Biochemistry, National University of Singapore, Republic of Singapore.
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