An overview of probiotic health booster-kombucha tea

Abstract

Traditional herbal medicine (THM) is a significant division of traditional Chinese medicine (TCM) that plays an important role in maintaining health and disease prevention. WHO has consistently highlighted the significance of traditional, complementary, and alternative medicine in human healthcare. Most people in Eastern Asia will start their day with a cup of tea. The tea provides a nourishing effect, and it has become an inevitable part of life. There are several types of tea, like black tea, green tea, oolong tea, white tea, and herbal tea. Besides the refreshments, it is important to consume beverages that benefit health. One such alternative is a healthy probiotic drink called kombucha, a fermented tea. Kombucha tea is aerobically fermented by infusing sweetened tea with a cellulose mat/ pellicle called SCOBY (symbiotic culture of bacteria and yeast). Kombucha is a source of bioactive compounds that include organic acids and amino acids, vitamins, probiotics, sugars, polyphenols, and antioxidants. Currently, studies on kombucha tea and SCOBY are gaining attention for their remarkable properties and applications in the food and health industries. The review gives an overview of the production, fermentation, microbial diversity, and metabolic products of kombucha. The possible implications for human health are also discussed.

1. Introduction

Probiotics are taken as dietary supplements to boost human immunity. The microbes in the gut are non-pathogenic and improve intestinal health. They also regulate nutrition, metabolism, and physiology. Fermented foods and drinks are traditional and trending probiotics that are available all around the world under different names. Fermented products are full of microbes that are responsible for conferring health benefits. Some of the fermented drinks include yogurt, Yakult, kefir, and kombucha. Kombucha is produced by fermenting starter culture; a mixed microbial consortium, with sweet tea infusions (Villarreal-Soto et al., 2019). In TCM, kombucha tea is known as the “Tea of Immortality” and the “Elixir of Life” (Soltani, Farshadfar, Shirvani, & Yaghotipoor, 2021). Kombucha is prepared by steeping black tea leaves in boiling water with the addition of some sugar (Fig. 1). Then the mother culture (symbiotic culture of bacteria and yeast, SCOBY) is placed into the mixture (Dufresne & Farnworth, 2000). The bacteria and yeasts in the SCOBY synthesize cellulose and form a cellulosic portion, and the fermented liquid is the tea portion (Vohra, Fazry, Sairi, & Babul-Airianah, 2019).

Fig. 1.

Preparation and fermentation of kombucha tea (Generally it involves adding tea to the boiling water followed by the addition of sugar. The fermentation is initiated by inoculation of SCOBY layer. After two to three weeks, it can be stored and consumed).

Kombucha is usually fermented in glass containers. To avoid contamination, the fermentation utensils must be sterilized. The opening of vessel should be wrapped in breathable fabric to forestall dirt and airborne mold. The incubation period of the culture is around 7 to 10 d at room temperature (18–30 °C). During fermentation, a gelatinous disc-shaped ‘daughter SCOBY’ is formed at the air–liquid interface. The biofilm formation depends upon the shape of container, and the thickness is determined by the duration of cultivation (Chan, Shin, & Jiang, 2018). The sugar and tea concentration and the fermentation time determine the colour and shade of kombucha. Due to the symbiotic action of the SCOBY, the pH diminishes when the acidity rises, which prompts gas bubble formation (Dufresne and Farnworth, 2000, Greenwalt, Steinkraus, & Ledford, 2000). After fermentation, the tea is converted into a probiotic beverage with improved health benefits. The tea seems to be an acidic beverage with a carbonated vinegar flavor. The end products can be stored in the refrigerator after straining it into a sterile jar bottle with a sealed lid. Chen et al. suggested that, as Kombucha is a living culture, it should be handled with care to avoid contamination (Chen & Liu, 2000). It can be easily brewed and well maintained in the home as well as in the laboratory. This ancient drink from China has been traditionally consumed for its therapeutic effects on the health of humans.

2. History

Kombucha tea originated in northeast China around 220BCE and was valued for its invigorating and detoxifying effects (Moreno-Jiménez et al., 2018). In 414 CE, Dr. Kombu used kombucha to cure the digestive problems of Emperor Inkyo, and by then kombucha had been brought from China to Japan. During World War II, the consumption of kombucha was extended beyond European countries, Russia, and North Africa (Blanc, 1996). After World War II, the cancer rates were lower in Kombucha-drinking regions of Russia than in nondrinking regions (Fontana, Franco, Lyra, De Souza, & De Souza, 1991). In the 1950s, Italian society reached its peak in the consumption of kombucha beverages (Dufresne and Farnworth, 2000, Hartmann, Burleson, Holmes, & Geist, 2000). In Germany in the 2000s, kombucha was devoured as a practical refreshment for the ailment, piles, and metabolic illness (Fu et al., 2014, Pei et al., 2020). Currently, kombucha imbibing has spread across the world as it is a natural diuretic. It is packed with healthy probiotics and helps to break down foods and flush out waste and toxins more quickly.

3. Biological composition of kombucha

The composition of the tea beverage and symbiotic culture of yeast and bacteria (SCOBY) layer is based on locality, weather, bacterial and yeast strains, and the inoculum source (Goh et al., 2012). Kombucha tea is comprised of osmophilic strains of yeast like Brettanomyces spp., Candida spp., Lachancea spp., Pichia spp., Saccharomyces spp., Schizosaccharomyces spp., Zygosaccharomyces spp., and acetic acid bacteria like Acetobacter spp., Gluconobacter spp., Gluconacetobacter spp., Komagataeibacter spp. and Lactobacillus spp. (Jayabalan et al., 2014, Teoh et al., 2004). The SCOBY yield is high during the first 14 d of the fermentation, and then the growth of the microbes will gradually decrease and altogether cease owing to adverse growth conditions (Chen & Liu, 2000; Jayabalan, Malini, Sathishkumar, Swaminathan, & Yun, 2010). In kombucha fermentation, fructose and glucose are utilized as the carbon source. Glucose is the only monosaccharide that produces cellulose pellicle. Each pellicle has a unique microbial composition which either possesses yeast culture or bacterial culture dominantly. The baby SCOBY that is formed after the fermentation of the mother SCOBY will even have a variation in microbial composition and percentage of microbial domination. There is a mystery about the metabolism of the microbes involved in fermentation. The microbial composition of the fermented tea and SCOBY layer determines the properties of the cellulose that is produced during the fermentation process.

4. Properties and application of bacterial cellulose

Kombucha fermentation is influenced by numerous physicochemical and genetic factors that ought to be improved, like the hardness of water, carbon source, substrate, the concentration of the tea, the microbial and media composition, production of CO₂, surface area, the effect of pH, time and temperature and oxygen supply (Marsh et al., 2013, Wolfe and Dutton, 2015). Improper assessment of these parameters will have an impact on the nutritional quality, biological activities, organoleptic and physicochemical properties of the beverage. The cellulose mat is a byproduct of the kombucha tea fermentation process. It is a valuable raw material for nano-cellulose production. Bacteria produce an unbranched pellicle structure that chemically equals native cellulose (Rangaswamy, Vanitha, & Hungund, 2015). Bacterial cellulose has unique properties that include increased mechanical potential, elasticity, nutritious, antibacterial, uniformity, thermally stable, high purity, hydrophilic, ion exchange, adsorptive, translucent, crystalline, biodegradability, adaptability, non-poisonous, permeable, fibrous nanostructure matrix, and excessive water clasping limit, good light transmittance, enhanced cell upgrading, detachment, and escalation (Chawla, Bajaj, Survase, & Singhal, 2009, Costa, Almeida, Vinhas, & Sarubbo, 2017, Morán et al., 2008, Shade et al., 2011). Bacterial cellulose has a wide range of applications (Fig. 2) due to its favorable properties, which include the food industry, ecology, paper industry, cosmetics, textile industry, nano-composites, biomedical and biotechnology fields.

Fig. 2.

Applications of bacterial cellulose (Niyazbekova, Nagmetova, & Kurmanbayev, 2018).

5. Metabolism of kombucha fermentation

Kombucha is bubbly, slightly sweet, slightly acidic, and is ingested throughout the world as a reviving refreshment (Sreeramulu, Zhu, & Knol, 2001). The bacteria and yeast in kombucha utilise substrates in different ways and are involved in many metabolic activities. During fermentation (Fig. 3), the yeast in the culture produces invertase and hydrolyses disaccharide sucrose into monosaccharide, glucose, and fructose, producing CO₂ and ethanol (Blanc, 1996). The acetic acid bacteria oxidize fructose into acetic acid and glucose into gluconic acid (Dufresne & Farnworth, 2000). The obligate anaerobic acetic acid bacteria in the culture oxidise ethanol and excrete acetic acid; thereby, the pH is lowered.

Fig. 3.

Kombucha metabolism during fermentation process (May et al., 2019).

Tea is comprised of catechins, theaflavins, thearubigins, flavonols, flavonol glycosides, protein, amino acids, caffeine, carbohydrates, organic acids (Balentine, 1992, Villarreal-Soto et al., 2018). After the fermentation process, kombucha tea is a cocktail of numerous chemical components (Miranda, Lawton, Tachibana, Swartz, & Hall, 2016). Acetobacter species are commonly found to be abundant in kombucha culture and are highly remarked as cellulose-producing bacterial species. The biochemical pathway involves Kreb’s cycle, Gluconeogenesis, and the Pentose Phosphate cycle, where the sugars are produced and converted into acids. At the end of the biochemical metabolism, the yeast and bacteria in the culture produce various beneficial metabolites.

6. Metabolites of kombucha fermentation

The metabolites of fermented tea consist of several acids such as acetic acid, gluconic acid, glucuronic acid, citric acid, l-lactic acid, (Malbaša et al., 2008, Malbaša et al., 2002) malic acid, tartaric acid, malonic acid, oxalic acid, succinic acid, pyruvic acid, saccharic acid (Chen & Liu, 2000), and d-saccharic acid-1,4-lactone (DSL) acid. DSL acid from d-glucaric acid has detoxifying and antioxidant properties (Bhattacharya, Gachhui, & Sil, 2013). The acetic acid concentration is inversely proportional to the fermentation time and also provides the taste of vinegar to the kombucha (Chen & Liu, 2000). Sreeramulu et al. has studied the antimicrobial effects of oxalic acid, saccharic acid, gluconic, succinic, and carbonic acids from kombucha, which helps to improve sleep (Sreeramulu, Zhu, & Knol, 2000). Glucuronic acid and malic acid from kombucha are helpful in the detoxification of the liver. It also beneficial in restricting lipid peroxidation (Jayabalan et al., 2008, Jayabalan et al., 2008). Kombucha yields monosaccharides such as glucose, fructose and also disaccharides like sucrose (Chen & Liu, 2000). Several vitamins are also obtained from kombucha fermentation, vitamin B1 with anti-ageing effect, vitamin B2 preventing arthritis and allergies, vitamin B12 aiding memory loss (Bauer-Petrovska & Petrushevska-Tozi, 2000), vitamin B6, which helps the body fight depression, stabilizes mood, and improves concentration, prevents stroke and obesity, and water-soluble vitamin C (Malbaša, Lončar, Vitas, & Čanadanović-Brunet, 2011) that suppresses the release of cortisol. Some trace amounts of alcohol (<0.5%) are usually produced in kombucha. The concentration of ethanol in kombucha is proportional to the fermentation time (Chen & Liu, 2000). The polyphenols from tea are active substances and powerful antioxidants (Malbaša, Lončar, Vitas, & Čanadanović-Brunet, 2011) are found in the kombucha beverage. The tea is widely known for its beneficial effects as it is rich in antioxidant content. Antioxidants play a role in preventing several diseases such as cancer, stress, neurodegenerative and cardiovascular diseases (Jayabalan et al., 2008, Jayabalan et al., 2008). Kombucha produced from green teas has higher radical scavenging activity than black tea (Chu & Chen, 2006). Essential metal elements like Na, K, Ca, Cu, Fe, Mn, Ni, Zn were found to be present in kombucha (Petrovic et al., 1999) Kumar et al. found the presence of anions such as F, CI, Br, I, NO₃, HPO₄ and SO₄ (Kumar, Narayan, & Hassarajani, 2008). Kombucha is widely consumed for the health benefits obtained from the numerous metabolites after the fermentation process.

7. Beneficial effects of kombucha

Kombucha tea is a functional food with several prophylactic and therapeutic benefits. The beneficial effects of this drink depend on the raw materials, type of sugar, fermentation duration, and composition of the starter culture. The biological activity of kombucha is determined by in vitro and in vivo studies using animal models and cell lines. Kombucha also possesses anti-inflammatory activity (Chakravorty et al., 2016; Vázquez-Cabral et al., 2017), antibacterial activity (Cardoso et al., 2020), anti-carcinogenic potential (Jayabalan et al., 2011), antimicrobial activity (Battikh et al., 2012, Sreeramulu et al., 2001), antioxidant activity (Chakravorty et al., 2016; Hartmann, Burleson, Holmes, & Geist, 2000, Jayabalan et al., 2008, Malbaša et al., 2011), and anti-proliferative activity (Cardoso et al., 2020, Deghrigue et al., 2013), which has been studied with in vitro experiments. Mice were used for the study of anti-oxidative effects of kombucha. It has an anti-oxidative stress against chromate (Ram et al., 2000), anti-oxidative stress against lead (Dipti et al., 2003), anti-stress activity against hypoxia and cold (Pauline et al., 2001), and protection against oxidative stress damage by induced alloxan (Bhattacharya, Gachhui, & Sil, 2013). The metabolites of kombucha prevent the leakage of myocardial tissues and provide protective cardiac effect (Lobo & Shenoy, 2015). It also protects against vascular and coronary heart disease (Isdadiyanto & Tana, 2019), and provides membrane stabilization in myocardial infarction (Lobo, Chandrasekhar Sagar, & Shenoy, 2017). Kombucha possesses anti-diabetic activity (Hosseini et al., 2016, Zubaidah, Afgani, Kalsum, Srianta, & Blanc, 2019) and provides a renoprotective effect against diabetes (Chandrakala, Lobo, & Dias 2019). Drinking kombucha can help to prevent and maintain the weight loss of diabetic rats (Morshedi, Dashti, Mosaddegh, Rafati, & Salami, 2006). Kombucha provides an anti-lipidemic and anti-atherogenic effect against alloxan diabetics (Aloulou et al., 2012, Lobo et al., 2017), Kombucha provides protection against nephrotoxicity activity by ceasing lipid peroxidation (Gharib, 2010). Bhattacharya et al. have studied the anti-virulence activity of kombucha against Vibrio cholerae in rabbits and mice (Bhattacharya et al., 2020). Adriani et al. studied the effects of kombucha and its cholesterol-lowering activity with duck blood (Adriani, Mayasari, Angga, & Kartasudjana, 2011). Cytogenic activity (Mrdanović, Bognadović, Cvetković, Velićanski, & Četojević-Simin, 2007) and changes in chromosomal aberrations (Yapar, Cavusoglu, Oruc, & Yalcin, 2010) were also observed in human lymphocytes. The longevity of kombucha consumption, life span, and general health was studied using mice (Hartmann, Burleson, Holmes, & Geist, 2000). Shenoy proved the hypoglycemic activity of kombucha by monitoring the blood sugar level in mice after kombucha consumption (Shenoy, 2000). Banerjee et al. conducted a study and proved that kombucha has the ability to heal stomach ulcers in mice (Banerjee et al., 2010). Kombucha helps to cease phenol-induced cytotoxicity (Yapar, Cavusoglu, Oruc, & Yalcin, 2010). Četojević et al. used the CHO-K1 cell lines from hamsters to study the protection against genotoxic effects (Četojević-Simin et al., 2012). However, most of the health benefits are not scientifically proven in human models yet. Clinical trials are yet to be done to manifest the claimed health benefits.

8. Side effects and health risks of kombucha consumption

Despite the benefits, there are some side effects and health risks to kombucha consumption. The Centers for Disease Control and Prevention (1994) stated that consuming 4 ounces of kombucha a day does not risk a consumer’s health. The US Food and Drug Administration conducted a biochemical and microbiological evaluation in 1995 that revealed kombucha consumption was secure in humans (Jayabalan, Malbaša, Lončar, Vitas, & Sathishkumar, 2014). Kombucha consumption can be harmful only if it is incorrectly prepared, and individuals with preexisting conditions should avoid it as it may lead to metabolic acidosis. As the kombucha culture has acetic acid and lactic acid, it possesses an acidic pH, which helps it protect itself by inhibiting the growth of harmful microorganisms (Chandrakala, Lobo, & Dias, 2019). The research rate on the stomach, skin, lactose intolerance, hyperlipidemia, and sensorimotor behavior is peaking continually (Martini, 2018). There have been substantial studies in animal models over the last decade on how probiotics and prebiotics regulate the metabolism of the host. These studies proved that intestinal flora modulates swelling, glucose metabolism, obesity, fullness, and energy consumption. In parallel to the emerging popularity and consumption of kombucha, there is a concern about its potential risks and safety issues. The major reasons for the beverage’s contamination include unreliable raw materials, vessels, packages, and a lack of sanitation during the fermentation process. This may lead to exposure to toxic metabolites and anti-nutritional components. Therefore, some protocols and norms should be framed by health and nutrition organizations to standardize production methods, raw materials, and quality control.

9. Conclusion and prospects

Fermented products are trending as they are healthy, beneficial foods that are consumed either knowingly or unknowingly by humans in their daily routine. It provides nutrition, enhances metabolism, and regulates the gut microbiome. Kombucha is traditionally brewed at home and is also commercially available. This beverage can be taken as dietary probiotic supplement rich in bioactive compounds, antioxidants and has a quantifiable effect on intestinal flora. Many articles provide claimed beneficial effects, microbial composition, physical, chemical, and biological properties, various raw materials, different applications, and traditional beliefs of kombucha, but there is still a dispute as there is a lack of research on toxicity studies of kombucha, microbial content of SCOBY, biological properties, consumer preferences, safety and invulnerability in kombucha consumption, qualitative and quantitative properties, probiotic effects, fermentation kinetics, cellulose chemistry, quality control, and sensory evaluation. The biological activity of kombucha is being investigated in cell lines and animal models. This particular beverage is consumed all over the world for its health benefits, but it hasn’t been involved or tested in any human trials. Human responses should be investigated to ethically claim the reported health benefits. A proper sensory evaluation study should be carried out to provide a clear view of the flavor profile, the consumer’s desire, and acceptance. As the drink is easily accessible, consumers should learn and practice the basics of brewing, storage, and handling to avoid risk. Sucrose is commonly used as a carbon source in kombucha brewing, which can be replaced by alternate sugar sources as a cost-effective raw material. There is a lack of determining the metabolites and other content in the end products of the fermented tea, and the microbial evolution should also be explored. SCOBY is termed “vegan textile” as it is used as an alternate for leather in the fashion and textile industries. As there are major issues with the flexibility and water absorptive properties, the research gap is to alter this property of the pellicle and to utilize it effectively. The SCOBY layer of kombucha can replace the traditional cellulose and the cellulose chemistry of the biofilm can be uplifted. Despite scattered safety issues, this functional drink is safe and can replace carbonated beverages. To summarize, every part of this miracle drink has major benefits in various domains and should be considered a boon from China. The industrial application of eco-friendly SCOBY is increasing tremendously because of its high potential and unique properties. Combining kombucha with other beneficial materials may lead to profitable and feasible innovations. As kombucha in the fermentation industry peaks to gain popularity, the unexplored areas of this beverage should be scientifically validated to level up the beverage for the next generation. The information in this article is expected to help fill in the research gaps and provide value for this Chinese wonder drink.

Authors’ contributions

Both the authors have read and approved the manuscript. The conception of work, drafting, revision and technical help were done by Kalaichelvan Gurumurthy. Data collection and material support were done by Suriyapriya S.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.