Studies On Kombucha Fermentation Process Optimization And Its Bacteriostasis Effect

Fermentation broth of Kombucha is a traditional acidic beverage tea with many sorts of microbes such as yeasts, lactic acid bacteria and acetic acid bacteria. The species and concentrations of microbes vary with different Kombucha. Fermentation broth of Kombucha has many nutrient ingredients such as functional elements of tea, live microorganisms and fermentation metabolites. This study explored fundamentally on the optimization of Kombucha fermentation process, the isolation and identification of predominant microbes, and the bacteriostatic mechanism of kombucha.The fermentation process was optimized using single factor test and orthogonal design methods. The results showed that the optimal medium compositions and fermentation conditions for kombucha production were: tea 0.6%, glucose 8%, liquid volume 300 ml, pH value 5.5 and culture temperatue 30℃. Under the optimum conditions, the fermentation broth had a bright and clear color, good biofilm formation, and high levels of nutrients.Four types of microorganisms were isolated and identified from Kombucha:three strains of yeasts named Pichia sp. L002, Wickerhamomyces anomalus strain L003 and Trigonopsis variabilis strain L004, respectively, and a strain of acetic acid bacteria named Acetobacter sp. L001. The further research of the fermentation process by single strain was carried out. The results showed that the four pure strains grew actively using black tea as material. The pH value of fermentation broth decreased, the free amino acids content increased, and some of the tea polyphenols conversed into theaflavins. Moreover, the alcohol producted by yeasts made kombucha sweet-smelling. Acetic acid bacteria and yeasts generated synergistically acetic acid, glucuronic acid and other acidic substances, which gave kombucha acid and refreshing taste.The fundamental study on bacteriostasis effect of kombucha fermentation broth was carried out. The results showed that when the fermentation process moved forward, the pH value of the broth decreased, the concentration of total protein and cell increased, and the bacteriostasis effect strengthened accordingly. The bacteriostasis effects of kombucha do not differ significantly when different tea substrates (green tea, black tea and Pu’er tea) were used for fermentation. When four kinds of broth fermented by four single strains were studied, only the broth by acetic acid bacteria had bacteriostasis effects on the tested bacteria strains. And the broth fermented by those four mixed strains had a more remarkable bacteriostasis effect than that by only acetic acid bacteria. Moreover, the effect of kombucha on Bacillus subtilis was stronger than that on Escherichia coli. When the pH value of fermentation broth was adjusted to 4.0, the impact of acid was excluded, there was still some bacteriostasis effect of kombucha. The results indicated preliminarily that some antibacterial protein existed in kombucha fermentation broth, and the bacteriostasis effect was due to the synergistic actions of high concentration acidic substances and inhibitory proteins.