 |
| Cy Lee pours canned green tea into a beaker. Photo by Rob Way/Cornell University. Copyright © Cornell University |
Today green tea is just as likely to be found in dispensing machines and in grocers' refrigerated cases in Europe and North America. But bottled or canned green tea instead of fresh-brewed? Clearly, there has been no comparison - until now. Cornell University food scientists have isolated the chemical compounds that are oxidized during commercial processing, and this discovery could pave the way for improved bottled or canned green-tea taste.
"When green tea is bottled or canned, the taste is not as good as fresh green tea. What we were looking to do is improve the flavor quality of it," says Chang (Cy) Y. Lee, Cornell professor of food science.
Lee and his students have isolated epigallocatechin (pronounced eppy-gallow-CAT-akin) and epigallocatechin-gallate as the major compounds responsible for changes in color and flavor when commercial processors try to bottle or can green tea. Preserving these compounds also is a health benefit because they are known to have anti-oxidant and anti-cancer activities.
Lee, Li-Fei Wang, Cornell doctoral candidate in food science, and Dong-Man Kim, of the Korea Food Research Institute, Hyonggi-do, South Korea, presented their talk, "Effect of heat processing and storage on flavanols [chemical flavors] in green-tea beverage," today (March 29) at the American Chemical Society national meeting in the Moscone Convention Center, San Francisco.
"First we had to figure out what's going on chemicalwise," said Lee, whose laboratory is located at Cornell's New York State Agriculture Experiment Station in Geneva, N.Y. "If the chemicals decreased during processing, then we have to modify the process to keep these chemicals stable after the processing."
How can the green tea compounds be kept stable? One possibility, Lee said, is to add ascorbic acid (vitamin C).
For nearly 5,000 years, the Chinese have consumed tea either for medicinal purposes or as a daily drink. In the early 17th century, tea was introduced into Europe, and at the end of the century, the East India Company brought tea to London for the first time.
There are two basic tea plants, C. sinensis sinensis, with small leaves, and C. sinensis assamica, with large leaves. From those two plants, three basic kinds of tea are derived: the fully processed or fully fermented black teas familiar to the Western palate; the semifermented oolong teas, familiar to Asia; and unfermented green tea.
Green tea starts with freshly harvested leaves which are processed by steaming at 95 to 100 degrees Celsius for about 30 seconds to deactivate enzymes and prevent the tea from fermenting. The leaves are then dehydrated for up to 40 minutes at 70 to 80 degrees Celsius, then rolled for 10 to 15 minutes. Two more dehydration steps complete the process.
For commercial canned or bottled green tea, hot water is added to the powdered form and the infusion is pasteurized by heating to 121 degrees Celsius for one minute. This allows it to remain on a grocery shelf without refrigeration. In addition to adding vitamin C, Lee and his colleagues are researching other ways to improve the quality of the bottled or canned green tea.