When you bite into a good sausage, the casing makes a cracking sound. This sound is characteristic of German knockwursts; sausage manufacturers use sensor technology to reproduce it. In addition to natural casings, many types of boiled sausages are enclosed in an edible collagen casing. This edible collagen-based sausage casing produces the expected sound when biting into a knockwurst, and it is suitable as a natural intestine substitute. Collagen-based sausage casings are produced using hydrolytic processes, which produce casings that are 50 - 70 µm thick. The collagen is produced from split cowhide, which is part of the dermis, and a by-product in tanneries. Pork rind or fish can also be used to produce collagen.

Collagen is the main structural protein in vertebrates. It is mainly found in connective tissue and the skin. Collagen is a by-product of leather production and has been used to produce sausage casings since the last century. In order to achieve better material and energy efficiency, i.e. save water, material and energy costs, the project group “Biotechnological process development for novel membranes based on collagen” is working on the biotechnological production of collagen-based sausage casings using enzymes and reduce the thickness of the material to approximately half of that of current sausage casings. The Biopolymers/Biomaterials cluster is funded by the German Ministry of Education and Research and brings together Naturin Viscofan GmbH, the Institute of Biological Process Engineering at Mannheim University of Applied Sciences, ASA Spezialenzyme GmbH, N-Zyme BioTec GmbH, the Bio-Logik-Control consultancy run by Prof. Dr. Peter M. Kunz and SUET Saat- und Erntetechnik GmbH. 

“In addition to reducing the material thickness to less than 50 µm, we would also like to introduce the use of collagen as a biobased material in other applications,” explains Dr. Hans Füßer, head of R&D at Naturin Viscofan GmbH. Naturin Viscofan GmbH is lead applicant in the project. “We are trying to move away from purely chemical hydrolytic processes,” says Füßer who also develops other collagen-based products for his company’s clients.

The figures show the split cowhide that is a by-product in tanneries (left-hand photo) and minced collagen mass (centre photo). The latter is a viscoelastic gel with fibrous components. The basic collagen mass (right-hand photo) has a dough-like robustness and consists of native collagen with an intact protein structure.

In order to reduce the thickness of the sausage casing, the project partners first had to analyse the fibre structures of the collagen that was previously used for this purpose. The collagen polymer is present as fibrils. The collagen molecules are offset in the fibrils, which gives an oblique banding pattern under an electron microscope. The quality of the collagen used for producing sausage casings is determined by chemically analysing the collagen’s fibre distribution. The collagen mass is centrifuged and the protein concentration of the supernatant is then determined. However, since the distribution of fibre bundle thickness and length has a substantial effect on the quality and property of the sausage casings, the project team developed a new, more precise method based on optical measurement of the fibres with a scanner. This enabled them to detect fibre bundles that were 10 to 200 µm thick.

In order to produce thinner collagen sheets, the scientists used enzymes instead of chemically treating the material with acids or lyes. They tested different enzymes for breaking up the proteins. Pilot experiments showed that different agents had different effects. “Thanks to better analysis methods, we found that collagen treated with protease no longer contained large fibre bundles,” says Füßer. “We successfully produced a collagen mixture containing fibres and fibre bundles of between 5 and 80 µm. This mixture gives the sausage casing excellent mechanical robustness.” 

Naturin Viscofan GmbH has already begun examining the use of the collagen mass in large-scale production, but optimal process conditions for the enzymes have yet to be determined. “The data generated in the project can be used as a basis for the product model,” says Füßer explaining that the project data will be very useful for collagen casing and foil end users. The project will also test the use of collagen foils as seed sheets. SUET Saat- und Erntetechnik GmbH produces seed sheets for the direct application of seeds in the field and for the cultivation of seedlings. In currently used seed sheets, the seeds are embedded between two sheets of paper. A few weeks after the seeds are sown, the paper decomposes and the seedling penetrates the germination medium. The project partners are working on replacing the paper with collagen foil and embedding the seeds between two layers of collagen. “We are hoping that collagen has superior properties to paper and will improve the germination process,” says Füßer.