Aims To study the mechanism of the antibacterial action of tea polyphenols such as catechins and theaflavins against Bacillus coagulans, and the interaction of epigallocatechin gallate (EGCg) or theaflavin 3,3'-di-O-gallate (TFDG) with the surface of B. coagulans cells was investigated. Methods and Results The antibacterial activities of EGCg and TFDG against B. coagulans cells were measured by counting of the viable cells after the mixing with each polyphenol. Bactericidal effect of TFDG was shown at the concentration of greater than or equal to 62 center dot 5 mg l(-1); however, at the same concentration, EGCg did not. According to the results of two dimensional (2D)-electrophoresis analysis, TFDG seemed to interact with cytoplasmic membrane proteins. The activity of the glucose transporters of the cells decreased 40% following the treatment with TFDG of 62 center dot 5 mg l(-1); however, this decrease was only slight in case of EGCg. This result was in accordance with the strength of their bactericidal activities. Conclusion Our results suggest that the direct interaction between membrane proteins and TFDG is an important factor in the antibacterial activity of polymerized catechins, affecting their functions and leading to cell death. Significance and Impact of the Study Tea polyphenols can effectively use the prevention of product spoilage in the food and beverage industry.