Development of a beverage from red grape juice fermented with the Kombucha consortium

Kombucha is a health-promoting fermented beverage traditionally made by fermenting a sweetened tea with a symbiotic culture of yeast species and acetic acid bacteria. The aim of this work was to develop a beverage using red grape juice as an alternative substrate. Grape juice contains various nutrient elements and phytochemicals, such as polyphenols, which possess a wide range of biological activities. We investigated the chemical characteristics and sensory and antimicrobial activities of the fermented grape juice Kombucha beverage. The pH decreased from 3.95 to 2.9 during the fermentation process and remained fairly constant thereafter, and the acetic acid bacteria and yeast counts in the broth increased up to 6 days of fermentation and subsequently decreased. Phenolic and anthocyanin contents and the antioxidant activity of the fermented beverage were higher after fermentation, with the maximum increase observed on the sixth day of fermentation when values were approximately 2.47- and 1.59-fold higher than pre-fermentation values, respectively, as assessed by 2,2-diphenyl-1-picrylhydrazyl and 2,2′-azino-bis (3-ethylbenzothiazoline-6- sulfonic acid) radical scavenging assays. Fourier transform infrared spectroscopy was used for the qualitative analysis of the grape juice before and after fermentation. Distinct peak variations in the spectral region between 2500 and 1650 cm⁻¹ were observed, which matched the appearance of organic acids and changes in phenolic compounds. Fermented juice Kombucha showed antibacterial activity toward all tested bacteria, which can be primarily ascribed to the increased production of acetic acid, but also to the biosynthesis of other metabolites, during the fermentation process. The 6-day fermented juice was the most appreciated by the taste panel based on the overall quality evaluation; with prolongation of fermentation the fermented juice acquired a distinct sour flavor.