New wraps help produce breathe, stay fresh longer.

As we know, refrigerated fruits and vegetables breathe, taking in oxygen and giving off carbon dioxide. Pairing this fresh produce with a wrapping or film best suited to the product's respiratory needs is able to enhance the length of time it will stay fresh and appealing.

The wraps, newer versions of the familiar clear-plastic films already used widely in home and commercial kitchens, act as modified-atmosphere packaging (MAP) systems that regulate the flow of oxygen and carbon dioxide to and from packages of produce. While the concept isn't new, ongoing experiments by USDA-ARS scientists offer some of the most up-to-date findings about the unique packaging needs of a half-dozen different fruits and veggies, including baby spinach, carrots, cilantro, iceberg and romaine lettuces and salad savoy--a nutritious new vegetable crop that is a close relative to kale and cabbage.

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.

When selecting packaging films for MAP of fruits and vegetables, the main characteristics to consider are gas permeability, water vapor transmission rate, mechanical properties, transparency, type of package and sealing reliability. Traditionally used packaging films, such as LDPE (low density polyethylene), PVC (polyvinyl chloride), EVA (ethylene vinyl acetate co-polymer) and OPP (oriented polypropylene) are not permeable enough for highly respiring products like fresh-cut produce, mushrooms and broccoli. As fruits and vegetables are respiring products, there is a need to transmit gases from and to the package.

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].