Light-protection for food packaging

Oxygen and light can alter the taste of foodstuffs. Manufacturers of packaging materials therefore try to protect contents from their influence. The latest approach is to use natural dyes in transparent plastic wrappers that selectively filter light.

Light and oxygen adversely affect the quality of most foodstuffs. In combination they cause various ingredients to undergo photo-oxidation. Fatty food substances become rancid and milk products develop an unpleasant “light-induced” taste. Certain ingredients such as the plant pigment chlorophyll or riboflavin (vitamin B2), exacerbate the loss of product quality due to their catalytic effect: they absorb light and transfer this energy to the oxygen, making it more reactive.

Manufacturers of food packaging are tackling these processes with two strategies: they either exclude oxygen by sealing packaging with nitrogen or they prevent exposure to light. The disadvantage of the first method is that the plastic must have a special sealing layer to prevent atmospheric oxygen permeating into the packaging. With the second method, the contents are only partially or not visible. But being able to see through the packaging is frequently desired for product presentation to customers.

At the Fraunhofer Institute for Process Engineering and Packaging IVV, researchers have adopted a new approach: they dye transparent plastic films with the very substances that are catalysts for photo-oxidation. In this way, packaging material remains almost transparent yet they filter out light in the critical wavelength ranges. One product that exemplifies this is olive oil: “Cold-pressed olive oils of superior quality are dark because they contain large quanities of chlorophyll. This tone is what the customer wants to see”, says Dr. Gertraud Goldhan, director of the Functional Films business field at the IVV. “Dying plastic bottles green using chlorophyll not only serves to emphasize this olive-green tone – the oil can also be stored for a considerably longer period of time under exposure to light.”

Using chlorophyll, the institut`s scientists have already been able to dye a whole range of different plastic materials used for packaging foodstuffs. To do this they employ a wide range of techniques: depending on the type and thickness of the film and the desired intensity of color, the chlorophyll is either added to the raw plastic prior to processing or it is applied to the prepared film as a coating. In multi-layered composite films it is incorporated into the laminating adhesives. There are also plans to develop printing inks containing the natural pigments. “Every product requires its own customized packaging”, summarizes Goldhahn. “With the experience gained, we are now much more oriented towards industrial manufacturers.”