Disinfection properties of the tea polyphenol epigallocatechin gallate in the presence of calcium ions

The antibacterial properties of tea polyphenols make them suitable for drinking water disinfection, but it is necessary to clarify the influence of metal ions on the sterilization efficacy. Epigallocatechin gallate (EGCG) was selected as a representative tea polyphenol, and the effects of calcium ion (Ca2+) concentration on its disinfection properties in Escherichia coli cultures were investigated. Changes in bacterial growth and structures were detected. The presence of low concentration Ca2+ (1–5 mM) inhibited the disinfection effect of EGCG but higher concentrations (6–10 mM) enhanced its effects. As Ca2+ concentration increased, the proportion of damaged bacteria also increased (15–43%). The presence of Ca2+ lessened the damaging effects of EGCG on the surface structures of E. coli but may have facilitated the entry of EGCG into the bacteria, enhancing its antibacterial efficacy. Tea polyphenols may be useful additives for the disinfection of groundwater and other raw waters containing calcium ions. HIGHLIGHTS Low concentration calcium ions inhibit the disinfection effect of EGCG, but high concentrations enhance disinfection.; Rate of EGCG-induced E. coli damage rises, as calcium ion concentration increases.; Calcium ions inhibit EGCG-induced damage to cell walls and membranes but promote internal structural damage.; Tea polyphenols may be useful for processing raw water with high calcium ion concentrations.