Antioxidant-Rich Foods Lose Nutritional Luster Over Time

April 3 -- THURSDAY, April 2 (HealthDay News) -- For those who swear by antioxidant-rich food and drink, two new studies show those health benefits can wane if the products are stored for too long a time.

The findings focus specifically on how well antioxidant activity holds up in commercially available green tea bags and olive oil when stored unopened and unexposed to light or moisture. And, in each case, the research revealed that steep drops in antioxidant activity take place within the first six months.

"The whole general concept driven by both of these studies is that if we want to maximize the nutritional value of the foods we eat, we really should buy only what we can use in a short period of time," observed Connie Diekman, a registered dietitian and director of nutrition at Washington University in St. Louis.

Diekman was not involved with either study, both of which are published in the March issue of the Journal of Food Science.

One study focused on the organic compounds found in green tea leaves that are known as catechins.

When consumed in tea, these antioxidant compounds are thought to have a bacterial and virus-fighting capacity, as well as the ability to inhibit cancer cell activity.

However, given that commercial green tea does not spoil and can be shelved for extended periods of time, Mendel Friedman and colleagues from the Albany, Calif.-based Western Regional Research Center of the U.S. Department of Agriculture set out to explore the stability of catechins during long-term storage in homes, restaurants, commercial warehouses, and/or stores.

The team chose eight teas sold commercially in tea-bag form in the United States, Korea and Japan.

The tea bags were kept stored in their original packaging in dark rooms heated to 68 degrees Fahrenheit for one of five different lengths of time: one week, one month, two months, four months and six months. Undesirable moisture exposure was not a factor.

After each period, the teas were ground into powder and mixed with boiling water, before being cooled and analyzed.