INTRODUCTION
The amount of secondary raw material obtained during slaughter and processing of poultry can be as high as 45% of the live weight of the birds. Most of this material is constituted by down and feathers, which have a high biological value, since they contain about 85% keratin.
Keratins are abundant proteins found in epithelial cells. They are major structural components of skin, nails, hair, feathers, and wool. Analysis of the amino acid composition of keratins shows that these proteins are a rich source of essential amino acids. However, the transformation of natural keratin into a digestible form is problematic, since keratins are fibrillar proteins and their mechanical stability is higher than that of all other materials of biological origin except chitin. The conventional techniques used for the processing of keratin-containing raw materials are neither efficient nor rational. The use of physical and chemical processing methods can result in formation of various toxic substances, as well as in loss of up to 75% of protein. Consequently, novel procedures for the processing and efficient use of the secondary raw material are needed.
Enzymatic methods for the processing of protein-containing raw materials, which became available due to the development of biotechnology, allow for the preservation of all essential amino acids. The use of ready-made enzyme preparations on an industrial scale can lead to a significant increase in costs and expenses, and therefore it is necessary to find solutions which enable the minimization of processing costs for the keratin-containing raw material. The use of live microorgan ism cultures in the processing of keratin-containing raw material allows for a reduction of the processing costs. The bioconversion method involves cultivation of the enzyme-producing strains on a substrate formed by the raw material to be processed. High efficiency of the subsequent decomposition of the substrate can be attained if this method is used. Selection of the optimal enzyme-producing microorganism and the optimal cultivation conditions is necessary in order to increase the rate and efficiency of bioconversion employing this method.
With the requirements concerning the strain and its functional efficiency taken into account, we chose the keratinase-producing strain Streptomyces ornatus S 1220. Simple composition and low cost of cultivation media, high levels of keratinase production, short cultivation time, and high enzyme yield [4] were the primary reasons for the choice of this strain.
The aim of the present work, formulated with the current problems taken into account, was to define the optimal composition of the cultivation medium providing for a high biomass yield of Streptomyces ornatus S 1220, to determine the most appropriate cultivation temperature and the period during which the rate of biomass accumulation is the highest, and to assess the effect of chemical additives on the specific enzyme activity. The tasks to be fulfilled in order to achieve the aim included analysis of the chemical composition of feathers, characterization of the effect of complex cultivation media on the yield of keratinase produced by the microorganism, analysis of environmental effects on the growth and productivity of the microorganism under investigation, and optimization of the cultivation parameters established.
