Kombucha is a fermented tea containing different probiotic species and postbiotics including antioxidants. Flavor enhancing additives are often added to kombucha to make it more appealing. It is unclear if these additives have any negative effects on the probiotic species and health properties of kombucha. The aim of this study was to analyze the effects of flavor additives on the organisms present in kombucha and examine the effects of these additives on antioxidants present. Probiotics were identified and analyzed following the addition of different concentrations of ginger, lemon juice, and hemp oil. Kombucha postbiotic polyphenol levels were analyzed using Ferric reducing antioxidant power (FRAP) assay. Two additives, ginger and lemon, had statistically significant inhibitory effects on S. cerevisiae and Bacillus sp. at concentrations of 2-3% and low inoculum density (OD600 0.05) indicating flavors have species specific effects based on probiotic density. Ginger did not cause significant inhibition of L. plantarum and only lemon caused significant inhibition at low inoculum density or higher lemon concentrations (OD600 >0.6). Hemp oil had caused significant inhibition of S. cerevisiae and L. plantarum hemp across all inoculum densities while Bacillus sp. showed significant effects at low inoculum density only. The FRAP assay showed that lemon treated kombucha had the great impact on antioxidant activity increasing it (5-15%), whereas hemp oil addition led to decrease in antioxidant levels (1-7%) indicating that some additives inhibit antioxidant production of the microbes present. The results indicate that additives have varying inhibitory effects on probiotic microbes as well as their postbiotic antioxidants. The effects of additives were greatly reduced at higher inoculum densities and lower additive concentrations. Overall, additive treatments can have inhibitory effects on kombucha probiotics and postbiotics including polyphenols.
Inhibitory effects of ginger, hemp oil and citrus juice on kombucha probiotics and postbiotic polyphenol production
Swain, S. J. (Author). 2025
Western Sydney University thesis: Master's thesis