Keratin2Protein; Valorization of keratinous materials through microbial conversion

The resource consumption by the human population is ever growing and with it comes an increasing amount of waste materials of which many are made from organic matter. The meat industry is generally considered as resource heavy, making it even more urgent that as much as possible of the byproduct produced is valorized. The focus of the Keratin2Protein project is on pig bristles and nails produced by slaughterhouses during preparation of the pig carcasses. Bristles and nails are part of a large family of proteinaceous materials (e.g. hair, wool, horn and feathers), made mainly from keratin and keratin related proteins. Because the materials are mainly made from keratin protein, the overall protein content generally exceeds 90% of the total biomass of the keratin material. Both bristles and nails are, however, very recalcitrant of nature, because of a high amount of chemical bonds (disulfide bonds) that makes it resilient to degradation by the proteases present in the digestive systems of most animals. To make the proteins available for degradation, treatment of the keratin material is needed. An alternative method for valorization of keratinous materials is the use of microbial organisms that can degrade the keratin and liberate easily degradable protein. Keratinolytic microorganism produce specialized proteases called keratinases, which can degrade the keratin. Furthermore, can the microorganisms break the disulfide bonds and further the degradation to produce digestible protein. In this PhD work different aspect of the keratin degradation process is investigated An assay was developed based on the degradation of the slaughterhouse by-product (bristles and nails) and was used for the evaluation of bacterial consortia grown on the by-product, to enrich for keratin degraders. Though many interesting bacteria were discovered, they were unfortunately all found to be potential pathogenic, thus not usable in the application. We did however manage to gain knowledge about potentially novel keratin degrading bacteria and their protease profiles. A known keratinolytic bacterium called Amycolatopsis keratinophila was acquired and studied to gain knowledge about its degradation mechanisms. Using a combination of different approaches involving protease purification, characterization and mass spectrometry, knowledge was gained on the protease profile of the bacterium. Two proteases were shown to be abundant in the culture supernatant of the A.keratinophila, purified and characterized, which showed that they were capable of degrading the slaughterhouse by-product. Furthermore, one of the protease showed promise as a biotechnological application by working at elevated temperatures. The protease profile was further elucidated by mass spectrometry, showing a wealth of potential keratinases in the culture supernatant. Further investigation will shed light on the roles of each protease. The culture supernatant showed high potential for degradation of the slaughterhouse by-product and optimization of hydrolysis condition (elevated temperature and pH stabilization), resulted in the 75% of the protein material in the slaughterhouse by-product being solubilized. Testing the digestibility of the end product showed >95% digestibility, indicating a successful valorization of the slaughterhouse byproduct.