You may have noticed new packages on supermarket shelves. Or, maybe you've heard the ads where Dick Cavett tries his best to convince you to try entrees that come right off the shelf.

What you might not have realized is that these new products are evidence of a revolution in food packaging."The forms of packaging we see on the shelves today are vastly different from those of 10 years ago," says Patricia Schwartz of the U.S. Food and Drug Administration's Center for Food Safety and Applied Nutrition. (Schwartz and Catherine Adams, of the U.S. Department of Agriculture's Food Safety and Inspection Service, gave a presentation on new packaging at the USDA-FDA Journalists' Conference held in San Francisco recently.)

What has caused this revolution and sent the packaging technologists scurrying to their drawing boards to dream up replacements for the old reliable metal cans and glass jars and bottles? The answer, says Schwartz, "is that food packaging has changed because the way Americans are eating has changed."

Consider a few statistics from Catherine Adams:

- 56 percent of women 16 years old or older are working.

- By 1995, it is estimated that 45 percent of households will be headed by singles or single parents.

- 75 percent of American homes have one or more microwave ovens. This reflects a 1,900 percent increase in the past 15 years.

- Meal preparation takes an average of 20-23 minutes now.

- Even when we eat at home, we are consuming home-prepared food with diminishing frequency. By 1990, it is predicted that 33 percent of all meals eaten at home will be take-out foods.

For the American consumer, convenience has become a very high priority, says Schwartz. "Food companies have responded to the consumers' demands with a myriad of foods that require a minimum of preparation. And, she says, the package plays an important role here.

"The role of the food package has expanded from simply protecting and preserving the food until a consumer brings it home. Increasingly, the package also serves as the container in which the food is cooked.

"Food companies have also switched to microwave compatible materials - plastic rather than metal - for more and more of their products."

In fact, she says, as research for her presentation she tried to find one of the old Swanson "TV dinners" in the three-sectioned metal tray, but there was not one to be found. "I discovered that Swanson gave the last metal tray to the Smithsonian in 1986."

Not just any plastics will do for these new packages, however. They must be made of materials that keep food quality, prevent growth of bacteria and, in some cases, can withstand high temperatures without changing composition.

And new packages have been developed that can extend shelf-life of foods in addition to increasing their convenience.

"Keeping a perishable product like milk fresh for six months without refrigeration is a sufficiently tall order that no single plastic material or even plastic-coated paperboard could do. So the packaging technologists developed a multilayer structure consisting of up to six layers of plastic, paperboard and aluminum foil. The laminated structures enable you to tailor the package to meet all the requirements of the particular food."

The sidebar on C1 lists some of the new kinds of packaging that are becoming available.

"These products fit easily into the changing profile of the home kitchen," says Adams. "A few minutes in the microwave, and supper is complete. It is not likely thatthese products will be cheap; but for those willing to pay for them, they offer good taste, excellent nutritional value and convenience with a capital C."

But there is another aspect consumers should be aware of: safety. The USDA and the FDA are both taking steps to ensure that the new packages will be safe and that food stored and served in them will not be compromised.

"By law in the United States a food package is considered a food additive," says Schwartz. "This is because components of the package can migrate or be transferred from the package to the food. For this reason, food packaging materials require pre-market approval by the Food and Drug Administration."

You can be assured that packages appearing on the supermarket shelves have been carefully tested and have passed all tests.

Another concern is the fresh-prepared, refrigerated foods that are becoming increasingly popular. "Refrigerated foods are not sterile and must be prepared appropriately by the manufacturer and handled correctly by the consumer to ensure that they are safe," says Adams.

The answer to this, she says, will probably be time-temperature indicators that will let the consumer know immediately if the product was kept at incorrect temperatures long enough to cause problems.

"Various markers are currently in the marketplace, although few have made their way to consumer packages. Reasons for this primarily include the evolving state of the art and the cost."

But this is something to watch for. And in the meantime, consumers need to take responsibility to see that the products are not kept at unsafe temperatures for any length of time.

If manufactured correctly and handled correctly by the consumer, she says, there is every reason these foods should be completely safe.

And there is no question but that the revolution in packaging offers consumers and food manufacturers what they demand: increased convenience, high quality and extended shelf-life.

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The new language of food

Here are some of the new packaging terms you will want to become familiar with as more of these products become available in the stores:

Fresh-prepared, refrigerated foods: A finished food that is not shelf-stable and may or may not be hermetically sealed (heat sealed with creation of an airtight seal) and must be maintained under refrigeration in order to retard spoilage or growth of bacteria. They have a refrigerated shelf-life of up to four weeks. Food quality is similar to things you would make from scratch, but the preparation time is cut substantially.

Modified atmosphere packaging (MAP): Food that is packaged with a specific mixture of gases (oxygen, carbon dioxide and nitrogen) that equilibrates with food components. The package materials are impermeable to gases, to keep the one mixture in and any other gases that would react with food out.

The process involves, first, the creation of a vacuum, then back-flushing with the appropriate gas mixture. Afterwards, the product is heat-sealed to retain the integrity of the package environment. The package resists crushing more readily than a normal vacuum-pack. Foods must be refrigerated.

Controlled atmosphere packaging (CAP): Similar to MAP packaging, except that a specific mixture of gases is maintained even after equilibrating with the food. The controlled atmosphere inhibits microbial growth and increases shelf life.

Sous-vide: The sous vide (meaning "under vacuum") process originated in France for use in the restaurant business, and still tends to be used in restaurants more than in homes, and still in France more than this country, but that is changing.

The idea is to prepare high-quality products in advance that can be kept refrigerated and then be heated only to taste immediately before serving. The minimal heat process retains more food quality than occurs with freezing, and foods can be prepared in less time than it takes to reheat frozen foods. Sous-vide products generally come in single-serving sizes.

Shelf-stable entrees: Hermetically sealed, heat-processed products similar to metal cans in principle, but taking advantage of new technologies to provide a high-quality product that requires no refrigeration and a short preparation time before serving. The products are processed in retortable (or able to withstand high temperature) plastics.

Retortable containers are now available in many shapes, including trays, cylinders, bowls and cups, and come with lids that are either peelable, semi-rigid or are metal pull tops. They are light-weight, unbreakable and can be used in either microwave or contentional ovens.

Aerosol-packed foods: A system is currently being proposed for beverages, condiments and toppings and may expand to other foods. The system incorporates a container with an expandable barrier pouch placed in the midsection. A carbon-dioxide propellant is created when sodium bicarbonate and citric acid are mixed within the pouch. The food is released much the way sprays and other aerosol products are now, except there are no flurorcarbons or hydrocarbons.

Heat susceptor packaging: Packaging for use in the microwave that features metalized surfaces that absorb microwave energy and become extremely hot, promoting the browning and surface crispness of packaged food as well as cooking it.

Aseptic packaging: Allows milk and other beverages to be stored for up to six months without refrigeration. The product is heated to render it sterile; and, in a separate process, the packaging material is sterilized. Then the sterile liquid is transferred to the sterile package and sealed, all in a sterile atmosphere.