antioxidant and antibacterial activity of kombucha beverages prepared using banana peel, common nettles and black tea infusions

backgrounds and objective: kombucha is a several thousand years old traditional fermented beverage originated from east. while black tea infusion is the common substrate for preparing kombucha, other herbal infusions can be applied for this reason too. common medicinal herbs or even waste herbal materials, like banana peel, could be suitable substrates for preparing kombucha analogues. in this study, kombuchas were fermented using nettles leaf and banana peel infusions.   materials and methods: herbal infusions were fermented by kombucha fungi. folin-ciocalteu assay was performed to evaluate total phenolic contents; free radical scavenging activity was evaluated using 2,2-diphenyl-1-picrylhydrazyl. disk diffusion method was performed to measure inhibitory activity against testing bacteria. all data were statistically analyzed by anova test at significant level of p≤0.05.   results and conclusion: black tea contained highest amount of phenolics (530.5 ppm gallic acid equivalent) and fermentation decomposed approximately 50% of phenolic contents to 265.5 ppm while phenolic content of nettles infusion and fermented beverage were 173 gae and 188 gae respectively and for banana peel, 136.5 gae and 155 gae; it indicated increase of phenolic contents due to fermentation that may be cause of protein contents of nettles and banana peel gone under fermentation by lactic acid bacteria. fermented beverage of three herbs had higher antioxidant potent than infusions. kombucha from banana peel showed the highest antioxidant activity by inhibiting 94.62% of dpph. while antioxidant activity of fermented beverages of black tea and nettles leaf were more related to their acetic acid content, it was found that a considerable part of antioxidant activity of banana peel kombucha was due to other acids and phenolics. no antibacterial activity was observed from either of samples. banana peel, as a waste herbal material, and nettles leaf are good ingredients for being used as substrate to make antioxidant kombucha beverage.