Sealed in edible film - consumable coatings

Science News, Jan 4, 1992 by Elizabeth Pennisi

For food scientists concerned with freshness and consumer satisfaction, moisture represents consumer enemy number one.

Water -- moving into, out of and between foods -- causes all sorts of problems. It forces manufacturers to package snack-pack cheese separately from the accompanying crackers; otherwise, the cheese hardens and the crackers grow stale. In cereals left too long on the shelf, raisins shrivel to tooth-chipping hardness. Frozen pizza crusts never taste quite right, because the sauce on top turns them soggy. Breaded shrimp shrink from water loss, sometimes so much so that they no longer meet size standards for legal sales. Celery wilts; fruit pie fillings get gummy.

All because water refuses to stay put.

Twenty years ago, most food scientists considered these problems too trivial -- or too intractable -- to warrant much attention. Today, however, the increased emphasis on global markets and higher quality means that foods need to stay fresh longer under more complicated conditions, says Ted P. Labuza, a food physical chemist at the University of Minnesota in St. Paul. In addition, concern about overflowing U.S. landfills has brought a clamor for reduced reliance on plastic and other containers.

"People complain all the time about how come you're wasting all the packaging," says Labuza.

Cheese-and-cracker snacks represent just one sort of "multitexture" product, in which differences between the components make packaging difficult. For frozen pizza, at least one company fries its dough slightly to give it a moisture-resistant coating oil, "but that gives a crust that is more like a pie crust," Labuza says.

And moisture isn't the only threat to palate sensibility. Oxygen seeps into foods, and fat molecules slip across food boundaries, affecting texture and taste, notes John M. Krochta, a chemical and food engineer at the University of California, Davis. He and other food scientists and engineers work hard to slow the movement of oxygen into fruits and to keep concentrations of carbon dioxide at levels that extend the shelf life of produce. They also seek ways to help maintain the identities of the various foods mixed together in convenience products. "You want to keep the food different," he explains. "You don't want it to all become mush."

These problems have driven food researchers to take a fresh look at an ancient preservation technique: edible films.

By coating products with an invisible and virtually undetectable barrier against moisture and gas, researchers like Labuza seek to extend the foods' shelf life while helping to solve the nation's solid-waste problem. With edible films, food distributors could prepare large quantities of fresh produce and make them available to customers at less cost than if buyers sliced, diced and cut the fruits and vegetables themselves. And all the waste peelings would be concentrated in one place, making disposal more efficient, notes Labuza. Edible films could also improve the availability of prepared foods, such as fruit-and-nut cereals or frozen pies.

"Consumption of fresh fruits and vegetables could be higher if this service were provided," says Attila E. Pavlath, a food scientist at the USDA's Western Regional Research Center in Albany, Calif.

Two years ago, Pavlath made a presentation on consumable coatings to a group of industry food scientists. Afterward, he received some 200 inquiries from sources ranging from a fast-food chain seeking to precut its onion slices to an ice cream manufacturer who thought a digestible film would keep frozen sandwich bars tasty.

Labuza envisions edible coatings in the form of spray-on films. Just as hair spray keeps hair looking freshly combed, a spritz of edible film on freshly peeled celery or chopped fruit could keep these foods looking their best for guests arriving hours or even days later, he says. Pavlath suggests spraying edible film on bread to keep sandwich fillings from making the bread soggy. Owen R. Fenema, a food chemist at the University of Wisconsin-Madison, wants to create an invisible packaging for pie fillings that melts and disappears during cooking. "The consumer would never know it was there," he says.

These films "can reduce the cost and complexity of the packaging system," says Krochta. Because an edible film may partially protect a product, the plastic wrap could be a single layer rather than a laminate of different polymers. "It may make [the wrap] recyclable," Krochta suggests. And with the edible films themselves, "the human being becomes the waste disposal mechanism," he says.

Although consumable coatings date back hundreds of years, scientists have much research to do before modern-day diners routinely eat the packages that protect their food. In the 13th century, Chinese vendors coated fruits and vegetables with wax to keep water in and to cut down on scratches and bruises. And in the 16th century, the English practiced larding, sealing perishable foods in fat. Today, however, these "edible" packages don't rate very highly in terms of palatability.