The black tea polysaccharides also exhibited the greatest activity for scavenging free radicals, which are linked to development of diseases such as cancer and rheumatoid arthritis, according to new findings published in the Journal of Food Science.
Interest in tea and its constituents has bloomed in recent years, with the greatest focus on the leaf’s polyphenol content. Green tea contains between 30 and 40 per cent of water-extractable polyphenols, while black tea (green tea that has been oxidized by fermentation) contains between 3 and 10 per cent. Oolong tea is semi-fermented tea and is somewhere between green and black tea.
The new research looked at the polysaccharide content of green, black and oolong tea, and measured their ability to inhibit the effects of alpha-glucosidase activity. By inhibiting this carbohydrate hydrolyzing enzyme, it is possible to reduce the spike in glucose levels in the blood following a meal (postprandial hyperglycemia).
If additional studies support the potential effects of the polysaccharides, it could see the black tea extracts positioned in the diabetic supplements market. An estimated 19 million people are affected by diabetes in the EU 25, equal to four per cent of the total population. This figure is projected to increase to 26 million by 2030.
In the US, there are almost 24 million people with diabetes, equal to 8 per cent of the population. The total costs are thought to be as much as $174 billion, with $116 billion being direct costs from medication, according to 2005-2007 American Diabetes Association figures.
“Many efforts have been made to search for effective glucose inhibitors from natural materials,” said lead researcher Haixia Chen. “There is a potential for exploitation of black tea polysaccharide in managing diabetes.”
Researchers from Tianjin University isolated three polysaccharide-rich fractions from green, black, and oolong tea. The black tea was found to contain lower molecular weight polysaccharides. Green tea had a range from 9.2 to 251.5 KDa, while black tea polysaccharides ranged from 3.8 to 32.7 KDa.
When tested for their ability to inhibit alpha-glucosidase, as well as antioxidant activities relating to hydroxyl radicals and DPPH radicals, the black tea polysaccharides were found to produce the best results, said Chen and co-workers.
“The differences in antioxidant activities and glycosidase inhibitory properties among the three polysaccharide-rich fractions appeared to be related to differences in monosaccharide composition and molecular weight distribution of the polysaccharide,” wrote the researchers.
Source: Journal of Food Science
Published online ahead of print, Early View, doi: 10.1111/j.1750-3841.2009.01231.x
“Physicochemical Properties and Antioxidant Capacity of 3 Polysaccharides from Green Tea, Oolong Tea, and Black Tea”
Authors: H. Chen, Z. Qu, L. Fu, P. Dong, X. Zhang