| Summary: | 碩士 === 國立中興大學 === 食品科學系 === 85 === Tea fungus (or Kombucha) is a home-brewed beverage which is
prepared by fermenting the sugar added in the black tea
decoction with a specific, butnaturally occurring starter. Tea
fungus is composed of two portions, a floatingcellulosic
pellicle layer and the sour liquid broth. Both acetic acid and
gluconic acids are the major ingredients found in the liquid
broth. The fermentation is usually carried out under
uncontrolled conditions, so the contamination of acid-tolerant
pathogenic microorganisms is poddible. Besides,it is difficult
to obtain an active and safe tea fungus if the starter was an
old one. It is therefore to investigate the feasibility of
preparing the teafungus by rsing pure cultures in this study.
Acetic acid bacteria and yeast flora were isolated, and some
were identified further, from 12 collections oftea fungi. The
Pichia mimbranefaciens, a film-forming yeast, was isolated
fromall the samples while other yeasts including Candida
sorbrxylosa, Dekkera bruxellensis A, Issatchenkia scutulata var.
exigua, Issatchenkia orientalis,and Schizosaccharomyces pombe
were present either two or three of them occasionally, depending
upon the sources of tea fungi. The viable counts of
microorganisms, particularly for acetic acid bacteria, decreased
graduallyduring a cultivation period of 60 days. The ethanol
content reached it''smaximum values (0.55-0.6%,v/v) after 14-20
days while the acetic acid reaches it''s maximum values
(0.8-1.5g/100ml) after 30 days. The gluconic acid content
increased with time and reached 4-5g/100ml after 60 days. The
sucrose was usedup, and the respective residual glucose and
fructose contents for some samples were about 1.2g/100ml and
5-7g/100ml at the end of fermintation. The curvivalcurves of a
pathogenic Candida albicans inoculated to tea fungi at various
growth stages were also studied. The results indicated that C.
albicans could survive from the acidic environment produced by
the tea fungus having a lower growth rate or acid production
rate during the early stage of fermentation;however, it died
rapisly if the tea fungus was an actively growing one. In the
study of co-inoculating a yeast with an acetic acid bacterium,
the S. pombe K-2 was found to be better than S, cerevisiae CCRC
20271 in the preparation of the tea fungus. The shaking culture
stimulated the production ofthe gluconic acid, but not for
ethanol, The consumption rate of sucrose was also closely
related to the viable count of yeast in tea fungus, and
sucroseconsumption rate by the yeast was faster than that of
acetic acid bacteria.Glucose, instead of fructose, was
preferentially used by the acetic acid bacteria. However, the
alcohol content increased initially in a two-stage cultivation
process, i.e. S. pombe K-2 was inoculated in advance and
cultivated for 5 days, but the subsequent acetic acid bacterium
failed to convert the alcohol produced efficiently in the sceond
stage. Besides, the carbon source was consumed rapidly by the
yeast, especially if large inoculum size and staticculture were
used. Consequently, the residual glucose concentration in the
teafungus was too low for the acetic acid bacterium to produce a
significant amountof gluconic acid. Finally, the current two-
stage cultivation process is not recommended for preparing the
tea fungus due to its less efficient production ofmajor
ingredients such as gluconic acid.
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