An Increase in Antibacterial Activity of Green Tea Infusion by Heat-Treatment

Abstract

Effect of heat-treatment on antibacterial activity of green tea infusion against Bacillus spp. was studied. After the green tea infusion was heated at different temperatures, the green tea components were partitioned with chloroform, ethyl acetate, and 1-butyl alcohol. The ethyl acetate soluble fraction was further fractionated by reverse osmosis. After heat-treatment, the green tea infusions were sterilized by filtration and then inoculated with spore suspension. B. subtilis grew in the green tea infusion heated at 95°C. B. subtilis didn't proliferate in the green tea infusion heated at 120°C, but grew in this infusion from which tannic components were removed by polyvinylpolypyrrolidone. Also the antibacterial activity against B. stearothermophilus in green tea infusion was increased by heat-treatment. Concentrations of caffeine, theanine, and amino acid in green tea infusion didn't change by heating at 120°C. While four kinds of catechins decreased and their epimers increased by heating at 120°C, the catechins and their epimers showed the comparable antibacterial activity. Both the ethyl acetate and 1-butanol soluble fractions from both unheated and heated green tea infusions exhibited antibacterial activity, and the activity of the fractions from heated green tea was stronger than that from unheated green tea. On the only heated green tea, the fraction not passing through the membrane retained antibacterial activity. From these results, it was suggested that antibacterial components produced in green tea infusion by heating were lower polymers of catechin.