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Protein-rich edible coatings for food.

In the classic Frank Capra film "It's a Wonderful Life," the key characterGeorge Bailey-is offered by an old school chum a "chance of a lifetime."

That chance is a foot on the ground floor of a new business venturesoybean plastics. George Baileyplayed by Jimmy Stewart-turns down the offer, and his pal winds up making a fortune in the business.

But chances like that only happen in the movies, right?

Try telling Frederick F. Shih of the Agricultural Research Service that such a notion is a pipe dream and he'll answer that you're wrong. A chemist at ARS' Southern Regional Research Center in New Orleans, Shih's found a new way to make a plasticlike material from soybeans.

"This research really has two benefits," Shih says. "It provides a substitute for synthetic petroleum-based plastics and it promotes the use of surplus soybeans in the United States."

Shih's process differs from a 1940's process for plastic auto bodies that simply incorporated soybean flour in phenol formaldehyde plastic.

Turning soybeans into films and coatings is a bit more complex than grinding the raw commodity, heating, and molding it into shape. Instead, Shih uses protein from the bean as the key ingredient.

In experiments at the New Orleans center's Food and Feed Processing Research Unit, Shih first soaked soybeans and then ground them aftff their texture softened. Mixing ground soybeans with water separates the protein from the solid.

Shih freeze-dried the protein solution to remove water from the protein. The result is a fine protein powder. He is working with two types of soy protein powders. One, known as soy isolate, contains more than 90 percent protein. The second is soy concentrate, which has about 70 percent protein.

The proteins can be mixed with various ingredients and additives before being cast into films or coatings for food products, Shih says. Sometimes, by using enzymes and other treatments, the protein can be modified for coatings and films with specific uses.

Other researchers have developed films and coatings from corn and wheat starches. But Shih says products made from soy protein may offer a bonus because of soy's adaptability for edible films.

"Protein can do a lot of things starch and gum can't do," says Shih. "It mixes better with oil, which is important in processing products and developing products with moisture-resistant characteristics."

And starch or gum can still be combined with soy protein to lend versatility to products. A common trait of films made of protein, starch, and gum is the ability to retain water and, at the same time, resist oxygen penetration.

By adjusting other factors, films and coatings can be tailored for effective food packaging and preservation.

For example, Shih says coating some food like meat products with these films generally retards moisture loss during short-term storage. But with time, the coating will eventually dry out and lose its ability to inhibit moisture loss from meat.

"Protein film actually attracts moisture, but its ability to repulse oxygen can also be significant for our purpose."

The soy protein coating could be useful in maintaining the original flavor of fat-containing foods. Precooked meat products, which might be used in institutional or school lunch programs, are particularly susceptible to developing an off-flavor, sometimes called warmed-over flavor.

"This defect is caused by oxygen penetrating the food and reacting with fats in the meat product," Shih says. "Coating food with protein films could solve the problem."

While moisture attraction and water migration may be a plus in some applications, they could be undesirable characteristics in other circumstances. In fact, an immediate goal of Shih's research is to reduce or control water permeability of the protein films.

Although edible coatings and films are essentially ready to use from a technical standpoint, they would first need approval from the Food and Drug Administration. And Shih says it may take another 2 to 3 years of research before the agriplastic can be used for nonfood products like garbage bags.

"Realistically, it's very difficult to replace synthetic petroleum-based plastics because soy-based plastic would be expensive. But, if consumers demand an environmentally acceptable alternative to synthetic plastic, it could speed up research and development in this area that might lead to lower product costs."

Shih is currently studying ways to improve the strength, elasticity, and moisture resistance of plastics made from soy protein. He is also working with various additives that could help retard microbial growth.

"This is an alternative way to produce films, coatings, and other plasticlike products from a renewable resource," Shih says. "And, because they are made from protein, the products have the desirable feature of being edible, nutritionally valuable, and, most importantly, safe to the environment."-By Bruce Kinzel, ARS.

Frederick F. Shih is at the USDAARS Food and Feed Processing Research Unit, Southern Regional Research Center, 1100 Robert E. Lee Blvd., New Orleans, LA 70124. Phone (504) 286-4354.
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Author:Kinzel, Bruce
Publication:Agricultural Research
Date:May 1, 1992
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