Film studies

If you've ever placed a minty breath-freshening strip in your mouth, you've encountered edible film. But where you may not have consumed it so consciously is with your peanuts, or on your grab-and-go fruit portion. In fact the development of whey- or sugar-based edible films has a very promising future in the food manufacturing industry. And so far they look set to do anything from prolonging shelf-life to preventing soggy pie-crust.

Perhaps the most exciting element to edible films is the sheer variety of potential applications. The nature of the products in development is such that when a film becomes approved for commercial use, potential uses are numerous.

"Although some edible films have been around and in use for several years, the technology has now found wide-ranging applications as the variety of available materials and their properties have broadened," explains a spokeswoman for Campden and Chorleywood Food Research Association (CCFRA).

"As well as providing a physical barrier and protective coating, edible films can help retain moisture and restrict its movement; limit fat migration between layers; provide a barrier to oxygen; act as an adhesive; help to trap flavour and aroma; and carry and present antioxidants or antimicrobials. Films can now be based on polysaccharides such as cellulose, starches and gums or proteins from milk, soya, and cereals."

This is exciting news for the food industry, and many manufacturers are looking forward to the many benefits which edible films can offer. As CCFRA states, the films in development are both sugar-based (polysaccharide) and protein-based. The former tend to be derived from the strong sugar structures found in plants, whereas protein films are most commonly whey-based.

While protein films have multiple uses in a protective or preservative role, polysaccharides can be used to bind or readily dissolve. In addition, fat-based films are being investigated for their ability to form oxidant resistant coatings. But there is also a large degree of overlap. Whey-based films can be water-soluble; polysaccharides can form barriers for the staggered release of products like multi-vitamins; and fat-based films can play a role in preventing water migration in foods.

So with technology continuing apace why aren't these products flooding our shelves? As with most advances in food science, progress is necessarily beholden to high safety standards. This means that while the technology may be in place to manufacture on a large-scale, many edible films are still being tested for wider use.

"There are many films in the development stages," says Pretima Titoria of Leatherhead Food International. Some are already on the market, such as waxes on fruits and vegetables; slow release formulations on supplements and pharmaceuticals; and edible films on poultry, meat and seafoods to extend shelf-life. But the application of edible films is slow due to safety and quality constraints required by the retail food industry and consumers."

Beyond breath strips

Breath strips are already widely sold, and the use of edible films in time-release vitamins is a less well-known, but nevertheless popular current use of the technology. But those behind the scenes are confident that these limited applications are just the tip of the iceberg.

" Within the area of edible films, there are a number of applications which we're likely to see quite soon," explains food processing expert Professor Barry Swanson of Washington State University. "Most obvious, perhaps, is the use of films to coat fresh produce so as to provide a barrier against environmental factors, such as oxygen and moisture. Or used as packaging with natural antimicrobials which can lead to extension of product shelf-life."

In addition to preservative applications, tough protein films are also being used to protect fragile products. Currently, this process has gained popularity with suppliers of shelled nuts, as it can help prevent their products from being damaged in transit. Manufacturers are also considering applications that keep ingredients separate from one another. "Certain films can be used to minimise migration within multi-component products," says Swanson. "For example, coating of nuts to prevent moisture absorption where moisture could come from ice-cream, or insertion of thin films to prevent migration from wet phases like custard to dry phases like biscuit in trifle products."

Currently, this concept is being tested in chilled pies - an area in which manufacturers continually look for new ways to prevent the dry pastry absorbing the wet filling and becoming soggy. So far, however, tests which use a film to separate the layers have proved rather too successful. Using a whey-based film to keep the filling separate worked so well that the pastry dried out too quickly, negating the shelf-life advantage of preventing moisture absorption. But the ability of films to separate wet and dry so effectively bodes well for future developments.

Those keen to take advantage of the public's obsession with health will also be pleased to note there are also possibilities in this area for edible films. "There are also health applications," says Swanson. "We've already seen films as breath-strips, but these could also act as carriers of nutriceuticals. We might even see the development of fat barrier films - for example the coating of French fries with specific cellulose gums can minimise fat absorption during frying."

The applications which Swanson refers to mostly relate to whey proteins, and this is perhaps the largest area for advances in edible films. The idea of coating products with sugar-based solutions, or fat to preserve and protect has been around for quite some time. But extracting proteins from existing products to produce edible films is a relatively new concept as it has only recently been matched with the technology to really expand its potential.

"Whey proteins make excellent oxygen, aroma and oil barrier films at low-to-intermediate relative humidity," says Dr John Krochta of Incredible Edible Films. "In addition, the mechanical properties of whey protein films are adequate to provide durability when used as food coatings, separating layers of ingredients in foods, or even films formed into pouches for food ingredients."

So while edible films have obvious preservative and coating applications, whey proteins can be made tough enough to form stand-alone food packaging. And due to the ability to manufacture either water-soluble or insoluble, this packaging could form a package which melts into food on cooking, as well as simply an alternative to plastic packaging. Uses for the latter in particular look set to become a strong driver for increased production of whey-protein films.

"The development of edible biopolymer films to replace petroleum-based plastics will evolve in the next five to 10 years as research progresses," says Titoria. Biodegradable packaging will become more and more important as we look to substitute certain recyclable paper and plastics with biodegradable materials, she adds.

Film critics

Although scientists may be propounding the multiple uses of edible films, industry views are mixed. The concept of a packaging, which melts into food and even acts as a thickening agent for sauce is, without doubt, an interesting one. But many processors fear that consumers will not be convinced. In addition, at these early stages, cost may also be a prohibitive factor.

US manufacturer TIC Gums, for example, was asked to engineer a film which could carry cheese and burger sauce for a well known hamburger chain. The idea was to create a product which could be very simply stored, come pre-portioned and was easy to add to burgers. Despite the obvious merits of this concept for the fast-food industry, however, the chain has not yet continued to pursue production, and TIC Gums suspects that the reasons are cost related.

Consumer perception is also a huge issue. With manufacturers moving towards clean-label products wherever possible, the idea of adding an unfathomable list of proteins and gums is unappealing. "How would the consumer feel about eating something that used to be a package?" asks Titoria. "That's something you have to think about when trying to promote this product."

Titoria also points out there could be problems with the development of edible films which take the place of packaging. "There are issues of safety with regard to tampering and maintaining reasonable assurance that the food was not contaminated or previously compromised in some way either intentionally or unintentionally," she says. "It may be more difficult to observe and identify tampering using an edible film with respect to plastic films and seals."

But that's not to say she's ruling out the concept in the future. "I don't believe one film will resolve the issues with many foods," Titoria concludes, "but edible films will be developed for selected foods to meet acceptable safety and quality standards."

Ultimately it looks like we'll have to wait and see which films prove themselves able to routinely meet the stringent demands of the food industry. It's still early days, but this is one film review that manufacturers will want to keep updated on. FM