The yeast spectrum of the ‘tea fungus Kombucha’: Das Hefespektrum des ‘Teepilzes Kombucha’

Abstract

Summary. The tea fungus ‘Kombucha’ is a symbiosis of Acetobacter, including Acetobacter xylinum as a characteristic species, and various yeasts. A characteristic yeast species or genus has not yet been identified. Kombucha is mainly cultivated in sugared black tea to produce a slightly acidulous effervescent beverage that is said to have several curative effects. In addition to sugar, the beverage contains small amounts of alcohol and various acids, including acetic acid, gluconic acid and lactic acid, as well as some antibiotic substances. To characterize the yeast spectrum with special consideration given to facultatively pathogenic yeasts, two commercially available specimens of tea fungus and 32 from private households in Germany were analysed by micromorphological and biochemical methods. Yeasts of the genera Brettanomyces, Zygosaccharomyces and Saccharemyces were identified in 56%, 29% and 26% respectively. The species Saccharomycodes ludwigii and Candida kefyr were only demonstrated in isolated cases. Furthermore, the tests revealed pellicle‐forming yeasts such as Candida krusei or Issatchenkia orientalis/ occidentalis as well as species of the apiculatus yeasts (Kloeckera, Hanseniaspora). Thus, the genus Brettanomyces may be a typical group of yeasts that are especially adapted to the environment of the tea fungus. However, to investigate further the beneficial effects of tea fungus, a spectrum of the other typical genera must be defined. Only three specimens showed definite contaminations. In one case, no yeasts could be isolated because of massive contamination with Penicillium spp. In the remaining two samples (from one household), Candida albicans was demonstrated. The low rate of contamination might be explained by protective mechanisms, such as formation of organic acids and antibiotic substances. Thus, subjects with a healthy metabolism do not need to be advised against cultivating Kombucha. However, those suffering from immunosuppression should preferably consume controlled commercial Kombucha beverages. Zusammenfassung. Der Teepilz ‘Kombucha’ ist eine symbiotische Lebensgemeinschaft von Essigsäurebakterien, darunter Acetobacter xylinum als charakteristische Species, und verschiedenen Hefen. Eine charakteristische Hefespecies oder gattung wurde bisher nicht identifiziert. Die Kombucha wird überwiegend in gezuckertem schwarzem Tee zur Herstellung eines leicht säuerlichen, moussierenden Getränkes kultivert, dem verschiedene Heilwirkungen zugeschrieben werden. Das Getränk enthält neben Zucker geringe Mengen an Alkohol sowie verschiedene Säuren, darunter Essig‐, Glukon‐ und Milchsäure, und antibiotisch wirksame Substanzen. Zur Charakterisierung des Hefespektrums unter besonderer Berücksichtigung fakultativ pathogener Hefen wurden zwei im Handel erhältliche sowie 32 Proben aus privaten Haushalten in Deutschland mit Hilfe mikromior‐phologischer und biochemischer Methoden analysiert. Hefen der Gattungen Brettanomyces, Zygosaccharomyces und Saccharomyces wurden in 56%, 29% bzw. 26% der Proben identifiziert, nur in Einzelfällen wurden die Species Saccharomycodes ludwigii bzw. Candida kefyr nachgewiesen. Darüber hinaus fanden sich im Probenmaterial die Kahmhefen Candida krusei bzw. Issatchenkia occidentals/orientalis und Species der zu den Apiculatushefen