Optimize packaging transmission rates to extend product shelf life.

Package wraps, or films, that cover precut produce offer protection against various bacteria and extend a product's shelf life. Often, the choice of film depends on the produce being wrapped.

Each film has an oxygen transmission rate, which allows cut produce to continue breathing throughout its storage and distribution. Hundreds of different films are commercially available, each with unique permeability levels. This feature must be matched with a particular fruit or vegetable variety's requirements. Another important issue involves the amount of oxygen infused into a package before it is sealed.

The key to maintaining quality and prolonging shelf life is to create the exact balance of oxygen and carbon dioxide inside a package, as is done with modified atmosphere packaging (MAP). USDA-ARS scientists have studied the oxygen and carbon dioxide transmission rates of package films, and how they affect the produce inside. Their research has led to the development of a balance of oxygen and carbon dioxide inside packages. This balance permits a specific fresh-cut produce variety to respire slowly and stay fresh for the longest possible time.

For example, fresh-cut cilantro-a leafy culinary herb that's a popular flavor component of tomato salsa-has a high respiration rate that makes its storage a challenge. Leaf yellowing, dehydration and loss of aroma can set in quickly after the product is cut. The packaging film that scientists have identified for wrapping cilantro provides a 14-day shelf life. Using similar packaging technologies, the technologists have been able to prolong the shelf life of romaine lettuce, iceberg lettuce, carrots and salad savoy, a nutritious new vegetable crop that is a close relative to kale and cabbage.

Researchers also have used acidified sodium chlorite (ASC) as a sanitizing agent on cut carrots. The chemical had been found to degrade produce. But by optimizing concentrations and dipping times, the team developed an ASC treatment that reduced E. coli O157:H7 levels on cut carrots by 99.999%. ASC was able to remove the bacteria that cause spoilage on carrots.

The specific formula and methodology hold promise as an alternative to the chlorine rinses many processors use to control microorganism growth on fresh-cut produce. Researchers have received funding to maintain produce freshness by slowing the ripening process with a gas treatment, 1-methylcyclopropene (1-MCP), alone or in combination with ASC. They have found that exposing cilantro to 1-MCP before cutting it, and then dipping it in ASC prolongs quality and slows decay when matched with the right film.

Further information. Yaguang Luo, USDA-ARS Produce Quality and Safety, Room 012, 10300 Baltimore Ave., Building 002 BARC-WEST, Beltsville, MD 20705; phone: [phone]; fax: [phone]; email: [e-mail].