From pre-packed Camembert to shrink-wrapped meat loaf – choosing the right packaging is a key issue in the food industry. Companies need to protect food products from oxygen, moisture and chemical and biological contamination while keeping them fresh for as long as possible. Transparent multilayer films, in which each layer offers specific benefits, are frequently used to protect food from contamination, with the best combination of layers being chosen for each specific product.

To minimize the amount of oxygen that permeates into the packaging, companies typically use expensive, petrochemical-based polymers such as ethylene vinyl alcohol (EVOH) copolymers. The German Society for Packaging Market Research (Gesellschaft für Verpackungsmarktforschung mbH) estimates that more than 640 square kilometers of composite materials employing EVOH as an oxygen barrier layer will be produced and used in Germany in 2014 – enough to completely cover Lake Constance. There is therefore a strong impetus to develop a sustainable packaging material which is both economical to produce and environmentally friendly. Researchers working on the “Wheylayer” project have been using whey protein instead of petrochemical-based polymers (see box) – and the results so far are extremely promising. “We’ve managed to develop a whey protein formulation that can be used as the raw material for a film barrier layer. And we have also developed an economically viable process which can be used to produce the multifunctional films on an industrial scale,” says Markus Schmid from the Fraunhofer Institute for Process Engineering and Packaging IVV in Freising.

First, some background: whey is a by-product of the cheese-making process and is produced in abundant quantities, with 90 percent of the milk used to produce cheese in Europe ending up as whey. Some 40 percent of this whey is disposed of, and Schmid adds that “the disposal of this whey represents a major challenge for the milk industry, especially with waste water regulations becoming more stringent”. But how is it even possible to make a barrier film from whey? The researchers from the IVV began by purifying sweet whey and sour whey and producing high purity whey protein isolates. They evaluated a range of different modification methods in order to obtain suitable proteins with outstanding film-forming properties. To enable these proteins to withstand the mechanical loads involved, they were subsequently mixed with differing concentrations of various softeners and other additives, which were also biobased. “All these additives are approved substances which are used in the foods we eat, for example glycerin and sorbitol,” says Schmid. 

The search for the perfect formula was a tricky process for the Freising-based researchers. For example, use too many softeners and the film becomes soft and flexible but its barrier effect against water vapor and oxygen decreases – in other words, permeation increases, which means that the food is no longer adequately protected. In the end, the researchers not only found the optimum formula, but also came up with a suitable, economically viable and industrial-scale method of applying whey protein coatings to plastic films and combining these with other films using different technologies. The overall process produces multilayer structures with barrier functions which can be used to produce flexible, transparent food packaging materials. “Our work at the IVV to manufacture a multilayer film of this kind using a roll-to-roll method is a world’s first,” Schmid notes. Companies that choose to make the switch to whey proteins in the future will only need to make minor modifications to their plants. The researchers have already applied for a patent on their new technology.

As well as being a renewable resource, whey also improves the recyclability of the composite materials. The polymers of EVOH-based multilayer packaging films cannot be separated into their constituent parts and recycled; once they are combined with other synthetic materials they can only be disposed of by incineration. But the situation is very different if a whey protein film is used instead of EVOH. “We developed the recycling method in collaboration with the University of Pisa,” says Schmid. The films are shredded and the whey protein coating is enzymatically hydrolyzed. The whey proteins, which are insoluble in water during their use as a packaging material, can be enzymatically split and washed away from the other composite materials. This separation process allows the various reclaimed constituents of the film to be sorted by type and recycled.

The IVV researchers are so convinced of whey proteins’ future potential as an alternative packaging material that they have initiated their own project in Freising which goes one step further. According to a survey carried out by the German Society for Packaging Market Research, there is not only an increasing demand for composite films, but also an increasing need for thermoformable composites. Growing demand for prepared products in trays is expected to increase the volume of these composites from 76,497 tons in 2009 to 93,158 tons in 2014. Currently, EVOH or films coated with silicon oxide are seen as the barrier materials of the future. “But completely replacing EVOH with silicon oxide coatings is virtually impossible. You can’t thermoform the material, so it can’t be processed as required,” says Schmid. The researchers are now working hard to replace EVOH in thermoform composites with a barrier film based on whey protein. This additional application for whey protein would likewise conserve resources and reduce the emission of carbon dioxide into the atmosphere.

To a layperson, the idea of replacing plastic with whey sounds like a joke – but the science behind it is very real. It is already possible to produce heat-sealed sachets, flow wrap and lidding films with barrier layers based on whey protein. The antimicrobial substances that occur naturally in whey also extend the shelf life of food products, and the whey protein film offers excellent biodegradability.

Researchers working on the joint EU-funded research project “Wheylayer” are aiming to develop new, sustainable packaging materials. They intend to use the outstanding barrier properties of whey protein films to keep out oxygen and moisture and aim to replace polymer layers in packaging materials with this natural product. Since 2008, packaging manufacturers, industrial associations, process engineers, recycling specialists, research institutes and producers of milk products have been working together to find a solution that fulfils the project’s objectives.

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