Effect of Water Hardness on Antibacterial Activity of Green Tea

Abstract

Effect of water hardness on antibacterial activity of green tea extract was studied using tap water and mineral water. The agar medium containing green tea made with six samples of tap water or two samples of mineral water, were tested for Escherichia coli culture, and the colony forming number was compared with that on the agar medium containing each water. Increasing water hardness resulted in increasing antibacterial activity of green tea. Using the high hardness (1468 mg/L) mineral water, the ratio of colony forming number on the green tea medium to one on the water medium was 0.016, which is 43 times lower than that on the low hardness (18 mg/L) tap water. The principal component analysis based on the concentrations of mineral elements in water samples, suggested that the high concentrations of Ca and Mg in water, and low concentration of Si increased antibacterial activity of green tea. The water hardness increased the amount of (-)-epicatechin gallate, not the total amount of catechins in green tea extract. The results are discussed considering the formation of complexs with catechin with Ca and Mg and the change in antibacterial activity of green tea.