German scientists see great prospects in grass biorefinery

German researchers affiliated with the University of Hohenheim see grass as a new protein source that can be used for pig and poultry farming. In the ProGrün project, they are not only investigating how grass can be used to obtain high-quality proteins for feeding poultry and pigs, but also for a range of other high-quality materials.

Grass contains a lot of protein, but without processing only ruminants such as cattle and sheep can make good use of the proteins. If the protein is released via a biorefinery technique, it is in principle also suitable as animal feed for non-ruminants, the researchers at the University of Hohenheim have shown in the ProGrün project. The rest of the biomass can also be used. For the production of high-quality materials, but also for heat and energy generation.

For the research, a biorefinery demonstration installation was built at the Agricultural Sciences Experimental Station of the University of Hohenheim at the research site ‘Unterer Lindenhof’. This allowed the entire process to be tested on a pilot plant scale. The grass is first shredded and pressed. The result is a press juice with a high content of soluble proteins, a residual amount of carbohydrates and other chemical compounds. The solid components and about two-thirds of the protein remain in a press cake.

Sugar, acids and other substances in the press juice can affect the digestibility of the proteins. Therefore, these are largely separate. The proteins are then gently dried, mixed with other feed ingredients and pelletized. In this way, protein-rich feed with 1,000 kilograms of protein can be produced from about 45 tons of freshly mown grass. The composition of the amino acids in the protein extract corresponds approximately to that of soy. Therefore, it is ideally suited for feeding chickens and pigs.

According to the researchers, it should eventually also be possible to use the obtained protein extract for human food. The press cake can be used to produce paper or fiber mats for insulation. Because it still contains sufficient protein, the press cake is also suitable for feeding to livestock. It can also be used in a biogas plant. The digestate can then serve as a fertilizer. Carbohydrates and sugars in the press juice are a promising starting material for the production of platform chemicals such as HMF, which forms the basis for the production of biobased plastics.


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