Theaflavin and its derivatives exert antibacterial action against Bacillus coagulans through adsorption to cell surface phospholipids.

AIMS: To investigate the antibacterial effects of tea theaflavins and catechins against Bacillus coagulans and the underlying mechanism of antibacterial action. METHODS AND RESULTS: Bactericidal activities of theaflavin and its analogues were evaluated and compared with that of epigallocatechin gallate. Theaflavin derivatives exhibited high bactericidal activity at 50 µmol L-1 , whereas epigallocatechin gallate did not, even at 500 µmol L-1 . Furthermore, we investigated the adsorption of theaflavins to model phospholipid membranes and corresponding effects on membrane fluidity to reveal their effects on the B. coagulans cell surface. Cell membrane fluidity was decreased after treatment with theaflavin derivatives with one or more galloyl moieties. Quartz-crystal microbalance analysis showed a strong affinity of the membrane phosphatidyl glycerol (PG) bilayers for theaflavin derivatives, correlating their bactericidal activity. CONCLUSION: These findings suggest that theaflavins could effectively inhibit B. coagulans by decreasing cell membrane fluidity. SIGNIFICANCE AND IMPACT: Bacillus coagulans is a spore-forming heat-resistant bacterium responsible for spoilage in low-acidic beverages. Natural antimicrobial components in tea-based beverages are central to reducing microbial contamination and product quality deterioration, although mechanisms underlying their antimicrobial action remain obscure. This study highlights the inhibitory action of theaflavins on B. coagulans and their potential application in food and beverage industries.