Canned foods have been getting the cold shoulder from a growing number of grocery shoppers lately -- not because of their nutritional content or their taste, but because the linings of most metal food cans contain the chemical BPA.
The ubiquitous chemical, also known as bisphenol A, is a hormone-disruptor that may contribute to developmental and reproductive problems.
In response, industry scientists are looking for alternatives.
Some companies already use BPA-free metal cans. But most continue to line their cans with epoxy coatings that have a BPA base -- and for good reason, said chemist John Rost, chairman of the North American Metal Packaging Alliance, Inc., an industry trade organization in Washington, D.C.
"They work better than any other material on all performance characteristics," Rost said, including corrosion resistance, physical flexibility and resistance to high heat during the sterilization process.
As a result, he said, today's metal cans are highly effective at preventing foodborne diseases, which kill 5,000 Americans, hospitalize 325,000 and sicken 76 million each year, according to estimates by the Centers for Disease Control and Prevention.
Food safety is high on the nation's priority list these days, with the Senate passing a bill on Tuesday that would overall the nation's food safety program. The bill, which needs to be meshed with a House version, would grant the U.S. Food and Drug Administration broader power to police food companies.
Canned foods, Rost pointed out, have not caused a single case of foodborne illness since epoxy coatings became the gold standard for canned foods more than three decades ago.
"There's a real food safety issue here, we have a technology that's been virtually flawless for over 36 years, and yet people are asking us to make changes," Rost said. "We want to make sure that any changes don't happen prematurely and affect food safety issues. We try to share with everyone the science on epoxy coatings so that they can see it's a real balancing act."
Food-canning technology has come a long way since the invention of the tin can in 1810. Today, companies use a variety of metals, including aluminum and steel. And they chose from many hundreds of epoxy linings, depending on the products involved.
The main purpose of a can's lining is to protect food from both bacteria in the environment and corrosion from compromised metal. To do that effectively, a lining needs to stay intact while in contact with food, a particular concern when the food is acidic.
The lining has to be flexible, to keep bending or denting of the can from exposing its contents to contamination. And it must be able to withstand high heat, which companies use for sterilization after filling cans with food and sealing their lids.
From an industry point of view, the lining should also be sturdy and stable. The longer a company's cans remain intact, the less money it loses in throwing spoiled products away. The invention of BPA-based coatings, Rost said, dramatically increased the shelf life of canned foods.
"When you pack a can with an epoxy coating, it can sit on shelves for years at a time and be completely safe upon opening and consuming," he said. "With older technologies, you will have cans fail over time much, much more."
But epoxy linings raise other concerns, said toxicologist Linda Birnbaum, director of the National Institute of Environmental Health Sciences in Research Triangle Park, N.C.
In a recent study, Birnbaum and colleagues found traces of BPA in a wide variety of canned foods from supermarket shelves. The study also detected far more BPA in canned foods than in fresh or plastic-wrapped foods.
It's not yet clear, she said, exactly what BPA's health risks are, what levels are cause for concern, or even where most of our exposure comes from, though it's starting to look like food is a major source.
"There is a lot of controversy," she said. "What we're trying to do with the research is get to the bottom of all this."
In the meantime, some alternatives are already available, and researchers are looking for more. Eden Organics, for one, lines its canned beans with baked-on oleoresinous c-enamel, which is what companies used before epoxy resins were invented. According to the company's website, Eden is the only American company to use cans with this lining, which is a "non-toxic mixture of an oil and a resin extracted from various plants, such as pine or balsam fir."
But oleoresins don't work for foods like sauerkraut or tomatoes, said Scott McCarty, director of corporate relations for the Ball Corporation, which manufactures metal food and beverage packaging, and makes BPA-free cans for Eden Organics. The acid in those foods eats away at the plant-based enamel.
Oleoresins also tend to leak into food, Rost said, affecting taste, smell and shelf life. Companies are working on a variety of other lining options, which use materials like polyester, acrylic, and vinyl. So far, all have drawbacks.
"Currently, there are no alternatives available to epoxy can coatings that will work the same and be as effective for all products packaged in cans," McCarty said. "We keep testing different coatings, but we're not there yet."
For now, consumers have some tough choices to make. Canned fruits and vegetables are often more affordable than fresh produce, but BPA-based linings have unknown health consequences.
On the other hand, BPA-free cans are far more expensive than the standard kind. Many types of canned foods aren't available in BPA-free versions. And even if a can is labeled as BPA-free, Birnbaum said, the food inside might still contain traces of the chemical.
"I know one company we questioned was supposed to be BPA-free, but our measurements of their cans showed it wasn't," she said. She wouldn't name the company.
© 2012 Discovery Channel