Edible Films and Coatings
What You Don't See is What You Eat
Edible coatings have come a long way since Grandma used an egg wash on her Swedish tea ring to make the crust shiny and golden.
Grandma now works as a greeter at Wal-Mart, and the production of edible films and coatings have become big business, serving demanding food consumers who insist that food be fresh, crisp, visually appealing and always available.
Some edible coatings are invisible. Some are so much a part of the food that we are not aware of them even though they may be visible. A savvy consumer who may be aware of the clear coat that an automaker put on his new car may not realize that his favorite fast-food restaurant is clear-coating his french fries.
Consumers are not keen on soggy french fries, dried out bakery goods or greasy fish. Stale nuts or chocolate gone gray stay on the shelf. No one wants the last six pills of a prescription, at $3 per pill, to turn to dust in the bottom of the bottle.
New coatings are coming to a market near you. One manufacturer is touting a film as a "precise combination of vitamins and minerals" that will keep cut produce fresh for up to three weeks under refrigeration. That dewy fresh slice of apple on the deli tray may be three weeks instead of three minutes old.
The most common coatings are wax coverings for fruits, lipid films to protect meat products and chocolate coating for a range of food items.
Edible coatings must be "Generally Recognized As Safe," a category established by the U.S. Food and Drug Administration.
Edible films may be cellulose ethers, starch, hydroxypropylated starch, corn zein, wheat gluten, soy protein and milk proteins.
Food-processing companies considering use of protein-based films should be aware that many consumers have a wheat gluten intolerance, milk protein allergies or lactose intolerance.
Those who think shellac is something that once coated furniture and has been replaced by polyurethane should think again. Shellac is one of the oldest substances for food coatings. A resin secreted by a tiny, female beetle as a means to hold her eggs to the bark of a tree, shellac is produced in India or Thailand.
After shellac is harvested, it is used to formulate confectioners glaze, which lengthens shelf life by providing a glossy finish for pan-coated candies such as chocolate covered almonds.
For some operations, shellac is no longer the best choice. Shellac resin glaze requires a solvent, such as food grade ethanol, to apply it. The ethanol is exhausted from the surface of the candy by air flow. In some regions of the United States, this ethanol exhaust is regulated, since the emissions contain volatile organic compounds that are restricted in many states. The strictest regulations on VOCs by states and the U.S. Environmental Protection Agency require processing operations to avoid VOCs whenever possible. Thus, other coatings are being used.
Food Science Australia researchers are looking to use naturally occurring compounds that come from the foods themselves in order to make edible coatings that are more like real food.
If food is raw or unprocessed, says Vic Reyes, a modified atmosphere coating can be applied to extend its shelf life.
"This kind of coating is similar to using a wax coating but will be more natural. The coating allows only certain gases to go through, which will prolong the freshness of the food," Reyes says.
MAC coatings are applied directly to the food. They reduce the need for plastic packaging and provide protection for the food.
Fried fast-foods have enjoyed explosive growth in the United States. Coatings are used to help fried foods stay crisp, making possible no-wilt french fries, which can remain under a heat lamp for 20 to 30 minutes.
Starch coatings, which may contain as many as five kinds of starch, coat the potato strips. The goal is to control water evaporation during frying. If the water cooks out too fast, the film coating tears and the french fries suffer. The coating allows uncooked fries to be frozen and thawed.
Clear starch coatings need not add flavor, but seasoning and coloring agents may be added to appeal to connoisseurs of spicy fries.
For those concerned about a diet too high in fat, edible coatings reduce the amount of fat that food takes up during frying. One manufacturer claims to have produced a coating that reduces the fat uptake in fried fish, vegetables, chicken nuggets and other foods by up to 40 percent.
In the pharmaceutical industry, edible coatings provide the control necessary for timed-release medications. Pills hold their shape without crumbling because of the coatings applied.
The Institute of Food Technologists' Expert Panel on Food Safety and Nutrition recommends that food labels list the materials used in coatings. "Use of such films as coatings on foods must be declared appropriately to the consumer, no matter how small the amount used. The nutritional quality of materials used for edible films may be affected, negatively or positively, by the temperature, pH, and/or solvents used in film preparation," the panel wrote in 1997.
But the institute says "no intrinsic nutritional or health problems have been identified for edible films." Edible films can be carriers of nutritional supplements, and protein-based films, depending on protein quality, can be an important nutritional enhancement of the food, the institute notes.
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