Effect of Green Tea Beverages on Efficacy of Povidone-Iodine

Abstract

Povidone-iodine (PVP-I) gargling solution is used to prevent bacterial infection, but because of its unpleasant smell and metallic taste, people often drink a flavoring agent, such as green tea, immediately after gargling. Green tea beverages, however, have antioxidant activity and may decrease the antibacterial activity of PVP-I. In this study, we investigated the interaction between green tea beverages and PVP-I. Addition of O-i ocha® or O-i ocha koiaji® caused color changes of PVP-I from amber to yellow-brown or to orange-yellow, respectively. Ascorbic acid (0.03 mg/ml) caused no color change in PVP-I. The antioxidant activity was highest in O-i ocha koiaji®, followed by Hajime®, Nama cha®, O-i ocha®, and Flavancha® in that order. Sou ken bi cha® and ascorbic acid (0.03 mg/ml) showed poor antioxidant activity. All six green tea beverages that we examined inhibited the antibacterial activity of PVP-I towards Streptococcus salivarius, Streptococcus mutans (S. mutans) and Streptococcus sanguis (S. sanguis). O-i ocha koiaji® showed the most potent inhibitory activity. The antioxidant activity was significantly correlated with the minimum inhibitory dilution ratio of green tea beverages for S. sanguis (r = 0.763, p < 0.05) and S. mutans (r = 0.854, p < 0.01). These findings indicate that green tea beverages reduce the antibacterial activity of PVP-I in proportion to their antioxidant activity. In conclusion, beverages with antioxidant activity, such as green tea beverages, should not be consumed immediately after PVP-I gargling.