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Coatings with good taste.

As the desire to reduce waste and use more natural materials pervades all aspects of everyday life, interest in newer packaging technologies has grown. To address both of these issues together, some researchers are investigating edible coatings derived from plant and animal-bassed ingredients. The goal is to develop films with no taste that extend the shelf of foods without the need for packaging materials.

Many foods today are vacuum packed in plastic and cardboard packages that end up in the trash. Different packaging systems are designed to protect perishable foods that are high in polysaturated fatty acids, such as nuts, meat, and fish, or those that are fragile such as breakfast cereal. These packaging materials often contain plasticizers and other typically non-biodegradable additives such as butylated hydroxyanisole (BHA) and butylated hydroxytoluene (BHT). These incidental additives in food packaging can sometimes be transferred to the food.


Edible coatings have the potential not only to provide the same protection as conventional packaging, they may also be formulated to contain added antimicrobials and even nutritional supplements such as vitamins and minerals or flavor enhancing compounds. Edible coatings are generally thin, transparent coatings that are prepared from edible materials such as polysaccharides, proteins, and lipids. In addition to serving as a coating, these materials can be formed into thin wraps or pouches. They not only act as a barrier to moisture and gases, but can also import texture and mouthfeel.

Currently, edible coatings can be found on many fruits and vegetables. Waxes, for example, provide a physical barrier against oxygen and moisture. Other edible coatings made from wheat gluten, cellulose, starch, and various proteins are used to line ice cream cones, coat battered frozen foods, and prevent moisture from being absorbed into pizza crusts in frozen pizzas. Water-dispersible forms of corn protein (zein) applied as a film on nut meats extends their shelf life byacting as an oxygen barrier. Edible coatings are also applied to the surface of snack foods and crackers to serve as a foundation or adhesive for seasonings. Animal intestines--and more recently, collagen--are used to hold sausage meat batter in a desirable form until heat set. Different edible films are also used to reduce oil absorption by battered and fried foods, from fish to chicken to french fries.



A confectioner's glaze made from the secretions of beetles from India and Thailand is often used on specialty confections like chocolate-covered nuts and raisins. One of the widest uses of edible coatings today is on M&M chocolate candies. The coating was developed to increase sales of chocolate during warmer summer months. The carbohydrate and gum-based coating keeps the chocolate from melting during handling and storage, but dissolves readily in the mouth.

While coatings such as waxes have been used for a long time, only recently has interest in exploring other possible edible coatings begun to grow. One impetus for this new interest can be attributed to the introduction and consumer acceptance of dissolvable thin strips as a delivery vehicle for mouthwash and cough medicines. Combine that acceptance with concern over increasing numbers of food-borne sickness outbreaks, and the market appears to be ready for edible coatings that can prevent salmonella or botulism contamination.

Edible coatings do present the opportunity to improve various qualities of foods. Researchers are exploring several different types of antimicrobial additives, such as organic acids (acetic, benzoic, lactic, propionic, sorbic), fatty acid esters (glyceryl monolaurate), polypeptides (lysozyme, peroxidase, lactoferrin, nisin), plant essential oils (cinnamon, oregano, lemongrass), nitrites, and sulfites. For fresh cut fruits, edible coatings provide an opportunity to prevent browning through incorporation of actives such as cysteine, N-acetylcysteine, and reduced glutathione instead of the typically used ascorbic acid, which has limited effectiveness. Texture enhancers such as calcium salts may also be incorporated into edible coatings to minimize softening of fresh cut fruits. Nutraceutical additives such as vitamin C and probiotics might also be formulated into edible coatings to improve the nutritional value of foods.


A number of different research groups are working to develop edible coatings that can be used with a wider variety of foods, particularly to prevent rancidity and bacterial development in meats and other foods and to protect fresh cut fruits and vegetables from browning, off-flavor development, and texture breakdown.

Mark Daeschel and Yanyun Zhao at Oregon State University are working on consumer-friendly antimicrobials by developing edible films made from fibers found in crab and shrimp shells that also contain lysozyme, a protein found in both eggs and human tears that has proven effective against listeria and staphylococcus.

Zhao recently investigated the impact that edible coatings have on extending the shelf life of pre-washed blueberries. The blueberries were dipped in the coating and then stored under various temperature and air flow conditions. Chitosan-based coatings (chitosan is a derivative of chitin, a natural substance often found in the exoskeletons of insects and crustaceans) were best at controlling mold growth. Semperfresh (SF), a sucrose ester, provided the best moisture barrier, while coatings based on the milk-derived protein calcium caseinate (CC) served as an excellent gas barrier.

At UC Davis, John Krochta has prepared a biodegradable film based on whey protein, a side product from the cheese making process. He is attempting to modify milk proteins designed to protect calves from bacterial infections and incorporate them into the film to inhibit bacterial growth.

Researchers at Rutgers University prepared biodegradable polymers with oils from oregano, cloves, or thyme that were then converted into antibacterial edible films. Films developed at the Department of Agriculture from fruits and vegetables themselves have been used as sushi wraps (a carrot film) and a ham coating (an apple film). There is also the possibility of incorporating cinnamon to fight listeria and salmonella and oregano oil, which can deter E. coli through the action of thymol and carvacrol.

There are hurdles to overcome before protective edible coatings can be widely used, however. Most formulations are water soluble and thus are very sensitive to humidity. Timed release of active antimicrobial agents and other nutritional or flavor enhancing additives is also an issue that is being investigated. Designing the coatings so that they still allow contact of good bacteria with the food is yet another challenge. Ways to incorporate actives--from antimicrobials to nutra-ceuticals--without affecting the natural flavor of the foods being protected by the edible coatings need to be discovered. Production scale-up and commercial application to foods must also be addressed.

Aside from these technical issues, there are other non-coating related problems to tackle. Labeling could be quite complex, such as listing allergens (if coatings are made from shellfish, wheat gluten, and milk proteins) and alerting vegans to the presence of milk-based products on fruits and vegetables, for example.

Even with these challenges, there is growing interest in the use of edible coatings as means to protect food while reducing the resource consumption and waste generation associated with the food industry.
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Publication:JCT CoatingsTech
Date:May 1, 2011
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