Antioxidants decrease an average of 32% after 6 months on the shelf, according to a 2009 study in the Journal of Food Science. These antioxidants, known as catechins, may decrease your risk of several types of cancer, but they are sensitive to both oxygen and light. Sadly, tea, unlike wine, does not improve with age.
Make It Last: "Buy tea in airtight packages such as tins, rather than cellophane wraps, which air can penetrate," advises Rona Tison of ITO EN, the world's largest supplier of green tea. Store your tea bags in sealed, opaque canisters in a cool spot. "Green tea is more sensitive to heat than black tea , so place your sealed container in the refrigerator to keep the leaves fresh and healthy for as long as possible," she says.
Canned tomato juice loses 50 percent of its lycopene after 3 months in the refrigerator—even when it's unopened, says a study in Food Chemistry. Similarly, scientists in Spain have found that the lycopene in ketchup deteriorates over time. That's a shame, because it's a potent antioxidant that may fight many forms of cancer and heart disease and even strengthen bones.
Make It Last: Skip the premade tomato sauce and make your own using boxed whole or diced tomatoes rather than pureed. Whole and diced tomatoes contain more solids, which provide added protection for the lycopene, says B. H. Chen, PhD, a food scientist at Fu Jen University in Taiwan who analyzes the stability of carotenoids. If ketchup sits in your fridge for months, buy smaller bottles, says Christine Gerbstadt, M.D., RD. Fresh bottles tend to start off with higher levels of lycopene.
Vitamin C declined 40 percent, on average, after 8 months in proper storage (in a place that's cool, dark, and dry), according to researchers in Holland. You probably wouldn't keep potatoes that long. But farmers often store them up to 5 months before shipping them to market, says Peter Imle, a potato farmer and plant geneticist in northern Minnesota.
Make It Last: Look for smaller potatoes (often labeled new), which have a slightly higher vitamin C content to begin with, and buy only what you can eat in a few weeks. Imle also recommends keeping potatoes in paper sacks, rather than plastic grocery bags. "Paper keeps out excess light and oxygen. But it still allows the potatoes to breathe, without trapping in moisture like plastic can," he explains. Here are some more tips to make stored foods last longer.