Use enzyme immobilization to produce bioactive packaging.

Enzymes improve the quality, performance and appearance of food. Incorporating enzymes within a packaging material, and creating a bioactive packaging system, is a niche area in the field of active food packaging.

Commercial examples of bioactive packaging are scarce, since complex enzyme immobilization processes can usually only be performed in a laboratory-like setting. The commercialization of bioactive packaging requires rapid and effective immobilization techniques.

Scientists at Purdue University wanted to see if ultraviolet (UV) polymerization could be a quick and inexpensive approach to immobilizing the enzyme glucose oxidase on food contact surfaces. UV polymerization is used for curing acrylic monomers and oligomers and involves the use of a photo-initiator (PI). PIs trigger free radical generation under appropriate UV wavelengths, causing complete polymerization in a fraction of a second. The scientists' research indicates that UV polymerization can effectively bind enzymes, with retained activity, to a food contact surface and act as bioactive packaging.

Introducing enzymes into an oligomer and PI matrix before curing it embeds them permanently to the cured polymer, creating a surface with bioactive properties. Researchers used two oligomers separately and a UV lamp to immobilize glucose oxidase onto corona-treated low-density polyethylene (LDPE).

The investigators tested the activity and orientation of the immobilized enzyme. They assessed the efficiency of their technique by testing the efficiency of glucose oxidase as an oxygen scavenger in apple juice at 25 C and 4 C. The retained activity of the immobilized glucose oxidase ranged from 85% to 89%, with a percentage orientation of from 90% to 95%. Immobilized glucose oxidase effectively reduced the oxygen concentration of apple juice from 4.6 ppm to 0.0 ppm in 30 minutes at 25 C, and in 70 minutes at 4 C when tested in a glass reaction vessel.

Many globular proteins, including enzymes, exhibit biological activity. Binding (non-covalent) and grafting (covalent) methods make it possible to attach globular proteins to polymer surfaces. The proteins can retain a portion of their biological activity but do not become a component of the food. Attached proteins can remove oxygen, improve or preserve packaged food and reduce microorganism levels.

The two principal disadvantages of protein attachment are the greatly reduced activity of some proteins during attachment and the drop in biological activity of the bound protein over time. But if these drawbacks can be properly addressed, a single- or multiple-attached protein system could potentially confer the properties of living tissue to a package.

Further information. Mark Morgan, Department of Food Science, Purdue University, 745 Agriculture Mall, West Lafayette, IN 47907; phone: [phone]; fax: [phone]; email: [e-mail].