Studies in the Microbiological Quality and Changes in Components During the Preparation of Tea Fungus

• Main Authors: Liu, Bih-Yun, 劉碧雲
• Other Authors: Chin-Shuh Chen
• Format: Others
• Language: zh-TW
• Published: 1996
• Online Access: http://ndltd.ncl.edu.tw/handle/92717621717207862391

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.