**1. Introduction**

Kombucha tea is a slightly acidic beverage that is produced from the fermentation of tea leaves (*Camellia sinensis*) and infusion with a consortium culture of acetic bacteria including *Acetobacter xylinum*, *A. xylinoides*, or *Bacterium gluconicum* and yeasts such as *Saccharomyces cerevisiae*, *S. ludwigii*, *Zygosaccharomyces bailii*, *Z. rouxii*, *Schizosaccharomyces pombe*, *Torulaspora delbrueckii*, *Brettanomyces bruxellensis*, *B. lambicus*, *B. custersii*, *Candida* sp., or *Pichia membranaefaciens* [1]. Normally, a traditional substrate used in kombucha fermentation is comprised of 10 g/L of black tea infusion that has been sweetened with.5–8% (*w*/*v*) sucrose. Notably, cellulose is produced during the fermentation by *A*. *xylinum* and appears as a thin film on top of the fermented tea where the cell mass of bacteria and yeast is attached. Yeast and bacteria in kombucha are involved in metabolic activities that utilize substrates in different pathways. Yeast cells hydrolyze sucrose into glucose and hydrolyze fructose using invertase

enzymes. Moreover, ethanol is also produced and further utilized by acetic acid bacteria to generate organic acids and other substances such as acetic, gluconic acid, glucuronic acid, citric acid, lactic acid, malic acid, succinic acid, saccharic acid, pyruvic acid, sugars, vitamins, and amino acids [2]. Thus, the pH value of kombucha is known to decrease during the process of fermentation due to the production of organic acids. Kombucha beverages also contain other substances such as phenolic compounds in a quantity of about 30% (*w*/*w*) of the dry mass of the tea leaves [3]. These substances vary considerably depending on the variety of tea and the processing procedures. Moreover, kombucha fermentation is dependent upon the source of kombucha culture (tea fungus), which is affected by a variety of properties for each kombucha beverage. When compared to unfermented tea, the enhanced beneficial activities of kombucha tea indicate that some changes are related to the origin of the microbial community that is present during the fermentation process [4–6].

Non-fermented tea such as green tea contains major polyphenolic catechins, such as epigallocatechin gallate (EGCG), epigallocatechin (EGC), epicatechin gallate (ECG), and epicatechin (EC) [7]. Black tea is considered a fully fermented form of tea since the production process creates a small particle size of the tea leaves and a greater surface area for enzymatic oxidation. During black tea fermentation, quinones react with catechins and produce new compounds; theaflavins and thearubigins [8]. In addition, catechins present in green tea are also partially converted to theaflavins [9]. Oolong tea is classified as semi-fermented tea and prepared during a limited period of oxidation. Thus, the fermentation process of oolong tea is shorter than that of black tea. Notably, oolong tea contains approximately half the amount of catechins when compared to green tea [10]. The compounds that are produced during the production processes of different types of tea markedly affect the composition and total phenolic content that are found in kombucha tea. The major polyphenolic components, catechin and epicatechin, are known to possess antioxidant activity [11]. Moreover, the antimicrobial activity of kombucha from black tea against pathogenic *Vibrio* strains was observed [12].

Although kombucha has been used for long time but scientific report on properties of kombucha has not been clarified. In this study, different biological properties of kombucha tea from various kinds of tea leaves including green, oolong, and black tea were determined for the useful properties of kombucha and application as supplementary beverage for health benefits. Hence, the aim of this study was to investigate the antioxidant and antibacterial properties of kombucha that was obtained from different types of *C. sinensis*, including green tea, oolong tea, and black tea, and the degree of toxicity it displays against the colorectal cancer cell line.
