něco o kombuše
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The microbiological composition of the tea fungus has been investigated. Bacteria and fungus present in Kombucha form a powerful symbiosis able to inhibit the growth of potential contaminating bacteria. The main acetic acid bacteria found in the tea fungus are: Acetobacter xylinum, A. xylinoides, Bacterium gluconicum, A. aceti, A. pasteurianus. Yeasts identified as Schizosaccharomyces pombe, Saccharomycodes ludwigii, Kloeckera apiculata, Saccharomyces cerevisiae, Zygosaccharomyces bailii, Brettanomyces bruxellensis, B. lambicus, B. custersii, Candida and Pichia species have been isolated from tea fungus. Aspects of the close association between microorganisms that make up the fungus and their interaction with the substrates supporting fermentation have been studied. Acetobacter xylinum has the ability to synthesize a floating cellulose network, which enhances the association formed between bacteria and fungi. The yeast cells convert sucrose into fructose and glucose and produce ethanol. Acetic acid bacteria convert glucose to gluconic acid and fructose through ethanol into acetic acid. Caffeine and related xanthines of the tea infusion stimulate the cellulose synthesis by the bacteria. Acetic acid stimulates the yeast to produce ethanol and ethanol in turn can be helpful to acetic acid bacteria to grow and produce acetic acid. Both ethanol and acetic acid have been reported to have antimicrobial activity against pathogenic bacteria thereby providing protection against contamination of the tea fungus.
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The main metabolites identified in the fermented beverage are: acetic, lactic, gluconic and glucuronic acids, ethanol and glycerol. Some chemical structures of important ingredients reported in Kombucha are given in Fig. 10. The presence of usnic acid in Kombucha reported once has not been confirmed in recent studies. Usnic acid had been previously identified in lichens and can deactivate some groups of viruses. The metabolite composition and concentration depends on the tea fungus source, sugar concentration, and the time course of fermentation. With 50 g/l sucrose, concentrations of ethanol and of lactic acid are optimal.
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A recent study reported the antibiotic activity of Kombucha against Helicobacter pylori, Escherichia coli, Staphylococcus aureus and Agrobacterium tumefaciens mainly related to the acetic acid produced during the fermentation. Tea extracts used at the same concentration did not exhibit any effect. The action of Kombucha intake on the nervous system could be associated with its content of the B complex of vitamins. The fungus is also used for medical purposes in skin therapy. The cellulosic pellicle formed mainly by Acetobacter xylinum during the fermentation of tea has been used as a temporary skin substitute on burns and other skin injuries.