Introduction
The great global trend in demand for healthy foods and drinks highlights that kombucha has attracted the attention of consumers. Kombucha's global market was valued at $1.9 billion in 2019, with a Compound Annual Growth Rate (CAGR) of 16.8 % from 2020-2025. The market is forecasted to continue its growth, reaching between USD 3.5 to 5 billion by 2025 (Intelligence, 2020).Kombucha is the name of the drink obtained by fermenting sweetened tea initially with Camellia sinensis - mainly black tea, but also other types of tea such as green and blue oolong tea - which serves as a substrate for fermentation and uses a symbiotic culture of bacteria and yeasts called SCOBY (Symbiotic Colony of Bacteria and Yeasts) (Coelho et al., 2020; Martínez Leal et al., 2018). The drink is prepared initially with tea, but variations made with infusions are possible. The drink tastes slightly acidic and carbonated (Martínez Leal et al., 2018).Moreover, recent research refers to kombucha, it is believed that fermented tea was first used in East Asia in 220 BC for its therapeutic effects. However, it originated in northeastern China (Manchuria) and was awarded the title of "Divine Che (remedy of immortality)" during the Tsin Dynasty (Ling Chi) for its detoxifying and energizing properties (Coelho et al., 2020; Kim & Adhikari, 2020). The drink spread in Japan in 414 AD. because a doctor named Kombu brought the tea to Japan and used it to cure the digestive problems of the Inkyo emperor, hence the name "Kombucha" or "Kombu tea "(Coelho et al., 2020). After that, the drink spread to Russia and Eastern Europe through trade routes (Coelho et al., 2020; Kapp & Sumner, 2019). Since then, the drink's popularity has increased.Since then, the fermented beveragehas been gaining popularity due to its therapeutic properties with antimicrobial effects (Khaleil et al., 2020; Tan et al., 2020), antioxidant (Osiripun & Apisittiwong, 2021; Xia et al., 2019), anticarcinogenic (Cardoso et al., 2020; Kaewkod et al., 2019), anti-inflammatory (Cardoso et al., 2021), antidiabetic (Hardoko et al., 2020), anti-bacterial (Cardoso et al., 2020; Lopes et al., 2021), among others applications (Morales, 2020).The beneficial effects of kombucha can be attributed to bioactive compoundsacting synergistically (Martínez Leal et al., 2018). In addition, the benefits are attributed to the presence of probiotic microorganisms (like some acetic acid bacteria and lactic acid bacteria), amino acids, tea polyphenols, sugars, organic acids, ethanol, water-soluble vitamins, and various micronutrients from fermentation (Coelho et al., 2020).However, despite the beverage's advantages, little research has examined the potential hazards and adverse effects (Alejandra Villarreal-Soto et al., 2018; Brews international, 2020; Martínez Leal et al., 2018; Villarreal-Soto et al., 2018). Added to this is the lack of regulatory frameworks that standardize the production of the beverage and guarantee the safety of consumers (Batista et al., 2022).This review aims to highlight the possible benefits and risks/side effects associated with the consumption of kombucha, as well as some regulations for the production and marketing of kombucha.
2. Health benefits
The health advantages of kombuchahave been demonstrated in the literature. Most of these studies are in vitro, and some in vivo studies are on rodents, small animals, and human peripheral blood lymphocytes. Some in vivo clinical trials are underway to understand kombucha's health benefits better (Kim & Adhikari, 2020).
Fig. 1. Chemical composition of traditional kombucha.
Most researchers have focused on antioxidant activity and phenolic compounds. However, a wide variety of bioactive compounds can be found in kombucha beverages, and the diversity of raw materials that can be fermented should motivate further studies analyzing the biological activities of released and produced peptides, lipids, and secondary metabolites, among others (Morales, 2020).This way, new functional beverages with high health benefits are developed using new plant-based sources with valuable bioactive compounds. The studies that evaluated kombucha's benefits in terms of its bioactive compounds are described below. The main results have been summarized.
2.1. Variables in the fermentation process can affect beverage properties
Process variables such as fermentation, temperature, and time, among other properties, can affect the amount of bioactive compounds, antioxidant properties, and composition of kombucha can be achieved by appropriate control of this variable (Ferreira & Salgueiro, 2021).
Table 1. Variables in fermentation process can affect beverage properties.
At longer fermentation, higher acidity, which may affect the product's taste, lower pH, and lower amount of bioactive compounds(Aung & Eun, 2022)Fermentation times with kombuchabioactive compounds and antioxidant propertiesThe highest values were recorded for the tested samples after 28 days of fermentation. After 14 days of the fermentation process, it was observed that the analyzed ferments were characterized by low cytotoxicity to keratinocytes and fibroblasts(Hordyjewicz-Baran, 2020)Infusion methods of the extracts in the kombucha fermentation processBioactive compoundsUltrasound-assisted extracts had higher organic acid content, particularly α-ketoglutaric acid (224.97 mg/100 ml) and acetic acid (564.15 mg/100 ml), with higher titratable acidity, lower pH, and increased DPPH scavenging capacity(Aung & Eun, 2021).Using bioreactorsBetter control of kombucha fermentationUsing these starter cultures in combination with shake cultures allows a better fermentation strategy to be applied and the safety of the fermentation processes(Sharifudin et al., 2021)Sugar concentrations and fermentation timesInhibition of α-glucosidase e enzyme for antidiabetic activity, total phenolics, total acids, and organoleptic characteristicsThe optimal treatment for inhibition was at a sugar concentration of 10% and a fermentation time of 14 days with an IC50 of 33.95 ppm. The kombucha from the fruits of R. mucronatahad a pH of 3.11 and a total phenolic content of 19,679.82 mg GAE /100g, 0.52% of total acids, which the panelists highly appreciated(Hardoko et al., 2020).
