Edible Adhesives

SpecialChem | Edward M. Petrie - Oct 25, 2006


This week's editorial takes a look at edible polymers in food packaging and adhesive applications. In these unique applications a food product is considered to be the substrate, and the adhesive must meet the ultimate food standard - the digestive process of the formulator. Bon Appetite!

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I was surprised recently to see significant development activity in edible films. Edible films have been around for a long time. Sausage casing made from animal intestines, and more recently collagen, allow meat batters to be held in a form until hard set. Wax coatings on fruits and vegetables prevent moisture loss, and these have been in use since the 1800s. Probably the most recognizable edible coating is a carbohydrate and gum based coating used to protect M&M chocolate candies from moisture and body heat until eaten. It also protects one's self from a messy chocolate covering on fingers.

One of the most useful functions of edible films is their ability to act as barriers, either to gas, oil, or more often moisture. Water-dispersible forms of corn protein (Zein) can be applied as a film for meats or fruits. One such application is the coating on raisins for use in dry ready-to-eat breakfast cereals. Edible films can also be used as a barrier to oil absorption in battered and fried foods. Methyl cellulose and hydroxypropyl cellulose have been used for these purposes.

An edible polymer will be generally recognized as safe ("GRAS") for use in edible films if the material has previously been determined safe, and its use in edible film is in accordance with current good manufacturing practices for food and used in amounts no greater than necessary to perform its function. In the U.S., if the edible polymer is not currently GRAS but the manufacturer can demonstrate safety, the manufacturer may either file a GRAS Affirmation Petition to the FDA or precede to make the material without FDA concurrence.

With all this going on in the area of edible polymers, I became interested in the possibility of edible adhesives and did a quick search. What I found is that sugar apparently isn't for sweetening anymore. Now it is the main ingredient in a new edible adhesive developed by Agricultural Research Service (ARS, Peoria, IL, USA) scientists. They developed a flavorless, food grade adhesive that could be used for an assembly line operation that inserts drinking straws into beverage cans, cartons, and bottles. Specifically, the company needed a strong, fast curing adhesive that could bond the straws to a special holder that's lowered into the containers before they are filled and sealed. At that point, the adhesive is to dissolve in the bottled liquid in an even and controlled manner; otherwise the straws would remain fixed to the holders instead of rising freely out of the container when consumers opened them.

The formulation and processes to form the sugar-based adhesives is described in a recent publication1and has been patented.2 Tests show that the resulting adhesive bond to substrates including wood, metal, cloth, leather, glass, plastic and paper. Besides holding the straws, the adhesives have potential applications in binding food items, utensil packaging, and manufacture of drug capsule layers.

Many foods we consume every day take advantage of edible coatings, and now edible adhesives are providing functionality as well. It remains, however, for food scientists to apply edible films and adhesives in other settings to fully utilize some of the properties of these unique packaging materials.

References

  1. "How Sweet It Is", Adhesives and Sealants Industry, June 2004.
  2. US Patent No. 6,613,378.

Should you have any comments or feedback, please contact me.

Edward M. Petrie

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