Citrus Juice Amplifies Green Tea Antioxidants

WEST LAFAYETTE, Indiana, November 14, 2007 (ENS) - Lemons and tea go even better together than their popularity might suggest. An assistant professor of food science at Purdue University has found that citrus juices enable more of green tea's unique antioxidants to remain after digestion, making the pairing healthier than previously thought.

The study compared the effect of various beverage additives on catechins (pronounced KA'-teh-kins), naturally occurring antioxidants found in tea.

Results suggest that complementing green tea with either citrus juices or vitamin C likely increases the amount of catechins available for the body to absorb.

"Although these results are preliminary, I think it's encouraging that a big part of the puzzle comes down to simple chemistry," said Mario Ferruzzi, assistant professor of food science at Purdue University and the study's lead author.

Dr. Mario Ferruzzi squeezes lemon juice into his green tea. (Photo courtesy Purdue)

Studies have shown catechins from the green tea plant, Camellia sinensis, are able to detoxify toxic chemicals, inhibit cancer cell activity and stimulate production of immune-strengthening enzymes.

Finding methods to increase uptake of these catechins may be important in improving health, part of the study's goal, Ferruzzi said.

The problem, he explained, is that catechins are unstable in non-acidic environments, such as the intestines, and less than 20 percent of the total intake remains after digestion.

"Off the bat you are eliminating a large majority of the catechins from plain green tea," Ferruzzi said. "We have to address this fact if we want to improve bodily absorption."

Ferruzzi tested juices, creamers and other additives that are either commonly added to fresh-brewed tea or used to make ready-to-drink tea products by putting them through a model simulating gastric and small-intestinal digestion.

Citrus juice increased recovered catechin levels by more than five times, the study found.

Ascorbic acid, or vitamin C, used to increase shelf life in ready-to-drink products, increased recovered levels of the two most abundant catechins by sixfold and 13-fold.

The study, published this month in the journal "Molecular Nutrition and Food Research," found that lemon juice caused 80 percent of tea's catechins to remain.

Following lemon, in terms of stabilizing power, were orange, lime and grapefruit juices.

Ferruzzi said both vitamin C and citrus juices must interact with catechins to prevent their degradation in the intestines, although data show that citrus juices have stabilizing effects beyond what would be predicted solely based on their vitamin C content.

"If you want more out of your green tea, add some citrus juice to your cup after brewing or pick a ready-to-drink product formulated with ascorbic acid," Ferruzzi said.

Ready-to-drink green tea products should optimally contain 100-200 mg of catechins, but oftentimes do not have sufficient levels of tea extract since some people do not like green tea's flavor, Ferruzzi said.

Although this study only examined green tea, Ferruzzi said he suspects that some of the results also could apply to black tea, which is produced by fermenting green tea. Many prefer black tea's flavor, although it contains lower total levels of catechins.

The study was funded by the National Institutes of Health.

To see if juices and vitamin C actually increase catechin absorption, researchers will have to find out if increased levels of intestinal catechins translate to higher levels of absorbed catechins in live animals and humans.

"This study tells us a lot of interesting things," Ferruzzi said, "but it raises many questions that have yet to be answered."

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