|An Update on Edible Films|
|Adapted from Food Technology, Vol 51, No 2, Feb 97, pp 60, 62-63
Scientific Status Summary by John M. Druchta and Catherine DeMulder Johnston
University of California-Davis
Lifeline, Spring 1997, Vol XV, No 2, pp 1-3
More than 300 million of them are produced each day. They are small, available in six colors and have a sophisticated edible coating. This sugar shell (a carbohydrate and gum-based coating) protects the user during handling, but allows the products to be readily consumed once in the mouth. If you haven't guessed by now, they are M&M's chocolate candies. Originally introduced in 1941, the reason was a lack of chocolate sales during the warm summer months. These candies are a good example of the application of edible films and coating. The coating solves the problem in an elegant and tasty manner: how to convey and keep intact meltable chocolate drops during shelflife and handling.
Edible films have been around for a long time. Sausage casings made from animal intestines, and more recently collagen, allow meat batters to be held in a form until heat set. Sausages are one of the earliest forms of processed foods. Wax coatings on fruits and vegetables to prevent moisture loss have been used since the 1800s. Edible coatings are not just laboratory playthings, and they are being used. However, according to Jerry Conklin, who works with cellulose films at the Dow Chemical Co., "Successful growth in the area of edible films will require a fusion of the technologies of food and polymer science." As the accompanying Scientific Status Summary suggests, we are steadily enriching our basic understanding of edible films. This understanding allows them to be used in target applications. And, several commercially available films and coatings give product developers an opportunity to solve very specific design problems.
Barrier. One of the most useful functions of edible films is their ability to act as barriers, either to gas, oil, or, more often water. Moisture levels in foods are critical for maintaining freshness, controlling microbial growth, and providing mouthfeel and texture. Edible films can control water activity preventing either moisture loss or uptake.
Water-dispersible forms of corn protein (zein) can be applied as a film or coating to provide a moisture or gas barrier for nut meats or fruits. One such application would be coating on raisins for use in dry ready-to-eat breakfast cereals. Here the zein coating prevents moisture migration from the raisins to the dry cereal helping to maintain their quality. In nut meats, zein coatings act as oxygen barriers and can increase shelflife by 50% by preventing rancidity according to Paul Freeman of Freeman Industries, Tuckahoe, NY, which markets corn zein formulations.
A similar product is Z*Coat TM (once called Cozeen in other reports) from Zumbro, Inc., Hayfield, MN. The coating consists of zein (corn protein), special vegetables oils, BHA, BHT and an ethyl alcohol carrier. The ingredients vary depending on the application such as no fat, no preservatives, or other considerations. It can be used to coat nut meats and confectionery products such as gummy bears, chocolate covered peanuts and licorice candy. According to the manufacturer, coated pecans held at 70 degrees F and 50% relative humidity had a shelflife of three months compared to one month for the uncoated pecans. The zein-based coating functions as a moisture and oxygen barrier and can fix antioxidants to the product surface.
Besides being moisture and gas barriers, edible coatings can act as barriers to oil uptake. Such coatings have found a niche application in reduced-fat battered and breaded foodservice. An edible system, called Fry Shield, developed and patented by Kerry Ingredients, Beloit, WI, and Hercules, Wilmington, DE, is one example. The system involves reacting to a pectin solution with bread crumbs or batters containing a calcium source. The film formed by the calcium-reactive pectin reduces the amount of fat uptake during frying. It is also said to reduce moisture loss increasing yields. The system can reduce the amount of fat uptake in fried fish, vegetables, chicken nuggets and other items during frying by 20 to 40%. Hercules has also explored a technology that used pectin as an oil barrier in French fires. This technology is based on the idea that since pectin binds potato cells together treating or infusing the tissue with pectin would improve resistance to oil penetrations. French fried potatoes prepared using the specially developed pectin absorb only one half the fat of regular French fries.
Gellan gum, a gum approved by the FDA as a stabilizer and thickener, reacts with mono- and divalent salts to form films. Gellan gum, marketed as Kelcogel ®, can also act as a barrier to oil absorption in battered and fried foods. According to Charlie Bowman, of the NutraSweet Kelco Co., San Diego, CA, gellan gum decreases oil pickup during frying as well as preventing batter blow off. Such gellan gum-based coatings have been used for several years in Japan and other Asian countries with tempura-type fried foods.
Methylcellulose and hydroxypropyl cellulose manufactured by the Dow Chemical Co., Midland, MI, have been used to decrease oil absorption during frying of French fries and onion rings. Methylcellulose has also been used to coat fruit and prevent moisture loss. Hydroxypropyl cellulose films are marketed by Watson Foods, West Haven, CT. The films are used to form pouches that allow processors to add premeasured amounts of additives such as colorants and vitamin premixes directly without further handling.
Binding. Edible coatings are applied to the surface of snack foods and crackers to serve as a foundation or adhesive for seasonings. Such coatings are especially useful in low-fat applications where the added oil of frying might normally serve as a seasoning adhesive. An example is oil-roasted and dry-roasted peanuts, which require an adhesive to act as a coating or bonding agent for salting and/or seasonings. In this application, modified food starches in combination with corn syrup, water and glycerin are used to make an adhesive solution. This solution is applied to the peanuts during tumbling. After the peanuts have been coated with adhesive, seasoning or salt may be added. Other materials that may be used as seasoning adhesives include Grain Procession Corp., Muscatine, IA, National Starch and Chemical, West Bridgewater, NJ, MBZ Group, Westport, CT and ExcelPro, Inc., Los Angeles, CA.
Glaze. Edible films can also act as glazes to enhance the appearance of baked goods. OptaGlaze marketed by Opta Food Ingredients, Cambridge, MA, is a wheat-gluten coating that replaces the traditional egg-based coating. The wheat-gluten film avoids possible microbial problems associated with raw egg products and provides some barrier properties against moisture loss.
Many foods we consume every day take advantage of edible coatings. It remains, however, for food scientists to apply edible films and coatings in other settings to fully utilize some of the properties of these "unique packaging materials."
Safety and Health Issues
Edible and Polymer Films. Determination of the acceptability of materials for edible polymer films follows procedures identical to determining the appropriateness of such materials for food formulation:
The materials that have received the greatest attention for edible films use are cellulose ethers, starch, hydroxypropylated starch, corn zein, wheat gluten, soy protein and milk proteins. Food processors considering use of protein-based films must be aware that some consumers have a wheat gluten intolerance (Celiac Disease), milk protein allergies, or lactose intolerance. 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. Aside from these considerations, no intrinsic nutritional or health problems have been identified for edible films. In fact, edible films can be carriers of nutritional supplement, and protein-based films, depending on protein quality, can be an important nutritional enhancement of the food.
Attention to the microbial safety of edible films is guided by standard considerations of water activity, pH, temperature, oxygen supply and time. Importantly, edible films are effective carriers of antimicrobials, which improve the microbial stability of film and food alike.
Biodegradable Polymer Films. FDA regulates all materials proposed for food packaging to ensure they are safe for food contact under conditions of intended use. There are several categories of biodegradable polymers acceptable for use as food packaging:
Non-edible, polymeric materials available for biodegradable polymer films include certain cellulose-based products (e.g., cellophane), microbial polyesters (e.g., polyhydroxybutyrate/valerate co-polymers produced by bacteria), biodegradable synthetic polymers (e.g., polylactic acid produced from fermentation lactic acid) and combinations of starch with biodegradable synthetic polymers (e.g., polyvinyl alcohol). Natural polymers or polymers derived from natural monomers offer the greatest opportunities, since their biodegradability and environmental compatibility are assured. Edible polymer film materials are also acceptable for biodegradable polymer films.
The challenge for the successful use of biodegradable polymer products is achieving controlled lifetime. Products must remain stable and function properly during storage and intended use, but then, biodegrade efficiently later. This means avoiding environmental conditions conducive to biodegradation at the intended time. Only by appropriately controlling water activity, pH, nutrients, temperature, oxygen levels, and time can package integrity and microbial stability be assured. Thus, biodegradable polymer films may be safely stored in dry environments and used with dry food products over a relatively long period of time, whereas acceptable time of storage in moist environments or time of use with moist foods would be limited.
Note: Persons interested in reviewing the entire Scientific Status Summary on Edible and Biodegradable Polymer Films; Challenges and Opportunities are referred to their local libraries or to Food Scientists in their area or at their state universities. Food Technology is a publication of the Institute of Food Technogiests, 221 North LaSalle Street, Chicago, IL 60601.
This and other Scientific Status Summaries are published by the Institute of Food Technologists' Expert Panel on Food Safety and Nutrition in Food Technology. Scientific Status Summaries, which are not necessarily written by the Expert Panel, are rigorously peer-reviewed by the Expert Panel as well as by individuals outside the Panel who have specific expertise in the subject area. IFT's Expert Panel on Food Safety and Nutrition, which studies significant food-related issues and oversees timely production of Scientific Status Summaries, comprises academicians representing expertise in one or more areas of food science/technology and nutrition. The Scientific Status Summaries may be reprinted or photocopied without permission, provided suitable credit is given.
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