Comparison of the antioxidant capacity and the antimicrobial activity of black and green tea

Tea is a common beverage. The green tea is preferentially recommended for its strong antioxidant properties and also for its antimicrobial activity. The antioxidant capacities of 30 samples (black and green tea) were determined by the chemiluminescent Trolox equivalent antioxidant capacity (TEAC) determination. The average value of TEAC of the non-fermented (green tea) and semi-fermented tea samples was 1.43 mM and the average value of TEAC of the fermented teas (black tea) samples was 1.43 mM. All samples were stored in freezer (−20 °C) and the TEAC determination was repeated after a year. The average values of TEAC of non-fermented and semi-fermented tea samples were twofold lower in comparison to fermented tea samples and only 20% of average value of TEAC of the fresh tea infusion. The parallel determinations of minimal inhibitory concentration (MIC) on gram-positive and gram-negative bacterial strains (Enterococcus faecalis, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli) were done. Also the MIC was possible to determine after a year. The assumed prevailing antioxidant and antimicrobial activities of non-fermented tea infusions were not confirmed as well as the dominant antioxidant and antimicrobial properties of specific type of tea infusion.