Consumer awareness of the benefits of green tea and green tea extracts continues to rise with growing numbers of studies, from 430 papers in 2000 to almost 1500 in 2003, reporting benefits of the main compounds, catechins.
This has seen European demand surge, having reached 500 metric tonnes in 2003. Companies such as DSM, with its Teavigo boasting 95 per cent purity of epigallocatechin gallate (EGCG), and Taiyo International, with its Sunphenon claiming more than 90 per cent purity, position themselves firmly in specific catechin markets.
The new study, published in the April issue of the Journal of Nutrition (Vol. 136, pp. 1043-1047), reports the effects of green tea extracts in the form of Mitsui Norin's commercial Polyphenon E (PE) on the cognitive learning ability of rats.
The concentration of catechins was classified as 63 per cent EGCG, 11 per cent epicatechin (EC), six per cent epigallocatechin (EGC), and six per cent epicatechin gallate (ECG).
The rats had their diets supplemented with either no PE (control group), 0.1 per cent PE in water, or 0.5 per cent PE in water for a period of 26 weeks, and their learning ability was tested using an eight-arm radial maze.
"Relative to controls, those administered PE had improved reference and working memory-related learning ability," said lead author Abdul Haque from Shimane University Faculty of Medicine.
"Furthermore, rats administered PE had lower hippocampus reactive oxygen species concentrations than controls. We suggest that this improvement in spatial cognitive learning ability is due to the antioxidative activity of green tea catechins," said Haque.
A different explanation of the benefits of catechins on brain function was offered recently, also by Japanese scientists, after a population based study of elderly people.
Reserachers from the Tohoku University Graduate School of Medicine said that EGCG is brain permeable, and its protection of the brain is proposed to be due to mechanisms other than its antioxidant and iron-chelating properties.
Possible mechanisms included "modulation of cell survival and cell cycle genes and promotion of neurite overgrowth activity."
The global tea market is worth about €790 (£540, $941) million, with green tea accounting for about 20 per cent of total global production, while black tea accounts for about 78 per cent.
Green tea is said to contain over four times the concentration of antioxidant catechins than black tea (green tea leaves that have been oxidized by fermentation), about 70 mg catechins per 100 mL compared to 15 mg per 100 mL for black tea.