Researchers publishing in Food Chemistry (link, sub required (1)) studied the anti-oxidative and anti-hydrogen peroxide (H2O2) activities of herbal teas. The herbs they studied were lavender, rose, chamomile, hibiscus, lemongrass, sage, rosemary, echinacea, thyme, peppermint, gingko, liquorice, and thorn apple. They compared their antioxidant properties and prevent the formation of H2O2 with those of green tea.
Herbal teas or tisanes are high in polyphenols, which as free radical scavengers have anti-oxidant properties. I thought I understood the reason why they studied H2O2 as in the body a highly level of H2O2 could lead to free radical formation and further oxidative damage, but the amounts produced, even by green tea are too small to be significant. In fact, some might even be helpful. Catechin derivatives in the teas have been previously shown to increase the formation of H2O2. The pH of the tea was a strong influence on H2O2 formation.
They prepared the teas by mixing 0.1 g dried herb with 10 ml H2O at 100 oC and steeping for 10 minutes before filtering. The filtrate was measured for total polyphenols, radical scavenging activity [for those who care radical-scavenging activity was measured by reaction with DPPH] and H2O2 concentration. The polyphenol concentration and radical-scavenging activity correlated to give a correlation factor of 0.950. Tea made from rose [do they mean rose hip?] was the only tea to have a higher polyphenol content and radical-scavenging activity than green tea. A factor put down to the anthocyanins present in rose; which are also responsible for the color. It is possible that rose has a high level of vitamin C which has anti-oxidant activity.
H2O2 formation did not correlate with either radical scavenging activity or polyphenol activity but may be related to pH as shown by the fact that echinacea tea had the highest pH and the highest H2O2 concentration. During incubation the H2O2 concentration increased only for green tea. If thorn apple (perhaps that it rose hip?) and hibiscus reduced the formation of H2O2 when mixed with green tea.
There was a similar article in the same addition of Food Chemistry (link sub req. (2)) which was looking at the antioxidant properties of extracts from large thyme (Thymus pulegioides rather than Thymus vulgaris).
1) Aoshima, H., S. Hirata, et al. (2007). “Antioxidative and anti-hydrogen peroxide activities of various herbal teas.” Food Chemistry 103(2): 617-622. Link
2) Loziene, K., P. R. Venskutonis, et al. (2007). “Radical scavenging and antibacterial properties of the extracts from different Thymus pulegioides L. chemotypes.” Food Chemistry 103(2): 546-559. Link