Antioxidant and antimicrobial activities of various leafy herbal teas

We evaluated the antioxidant and antimicrobial activities of various leafy herbal tea (LHT) extracts, including rooibos, green tea, black tea, rosemary, lemongrass, mulberry leaf, bamboo leaf, lotus leaf, peppermint, persimmon leaf, and mate tea. To compare the antioxidant activities of various LHTs, samples of each were extracted with 80 °C water or 20 °C ethanol, and their total phenolic content (TPC), total flavonoid content (TFC), 2,2-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity, 2,2-azinobis-3 ethyl benxothiazoline-6-sulphonic acid (ABTS) radical cation decolorization activity, ferric reducing power, and ferrous ion chelating effect were measured. Green tea ethanol extract showed the highest antioxidant activity in all assays except the ferrous ion-chelating assay. Water extracts of green tea and black tea and ethanol extracts of rosemary, mate, and persimmon leaf teas also exhibited considerable antioxidant potential, followed by the green tea ethanol extract. Minimum inhibitory concentrations (MIC) and minimum lethal concentrations (MLC) were determined to verify the antimicrobial activities of the LHT extracts against two oral pathogens (Streptococcus mutans and Streptococcus sobrinus) and three food-borne pathogens (Listeria monocytogenes, Shigella flexneri, and Salmonella enterica). Among the tested LHTs, green tea ethanol extract had potent antimicrobial activity against all five pathogens, and the mate tea water extract was the most effective against Gram-positive bacteria. Consequently, green tea ethanol extracts had the most powerful antioxidant and antimicrobial properties, suggesting their potential application as a health-promoting functional ingredient or natural preservative in foods.

► Antioxidant and antibacterial functions of leafy herbal teas were verified. ► Green tea was most antioxidant as well as antibacterial against oral and food-borne pathogens. ► Drinking herb teas provides antioxidant compounds, mainly water-soluble polyphenols. ► Drinking herb teas improves dental health by eliminating cariogenic bacteria from oral cavity. ► Leafy herbal tea extracts may have the potential as natural preservatives in various foods.