## 4 Discussion  
The practical applicability of the microencapsulation technology within yeast cells, described previously [25], depends on the availability of affordable substrates for cultivation of the producer strain, and not only on the yield of the enzyme. _Y. lipolytica_ is known for its ability to reduce the peroxide index of the substrate and its overall detoxification of the different types of organic waste [31; 32; 33]. The yield of the active enzyme in microencapsulated form at the end of fermentation is usually significantly inferior to the yield of the secretory enzyme. However, this is compensated by the low cost of raw materials for cultivating yeast strains, and the waste-free manufacturing circle and energy savings at the drying stage (a microencapsulated enzyme, unlike a secretory one, can be concentrated by centrifugation instead of membrane filtration or vacuum evaporation followed by spay drying). We also assume that microencapsulation of the enzyme can significantly increase its biological activity within the feed additive per unit of activity, since such an enzyme, unlike the secretory one, will not lose activity when passing through the stomach. We also assume that the microencapsulated enzyme will more efficiently cleave the phytate released from the grain in the intestine, since the processes of release of phytate from the swelling grain in the duodenum and the release of phytase from microcapsules will proceed in parallel, and the phytase will not be degraded by pancreatic proteases while the phytate is still spatially isolated from it by seed shells. Swing blood is a massive type of the organic waste is rich in fat. To the best of our knowledge, swine blood has never been previously reported as a substrate for cultivation of _Y. lipolytica_. It can be hypothesized that it can be applicable for this; however, its nutritional value as a feed additive is limited because it contains an excess of iron, which is unfavourable for growth of the microorganisms. This was confirmed with a low yield of the specific activity 360 FYT/L. In comparison to the reported activity of OPP 340,000 FYT/L produced by the same strain PO1f (pUV3-Op) in a medium with peptone and glucose [25], this is an extremely low yield. The yield of the wet biomass was about 200 g/L of the wet cells together with the residue of the blood clot that was converted to the powder with the final yield of 30 g from 1 L of the culture. This powder after spray drying at 70 \({}^{\circ}\)C had activity 55 FYT/g. As far as the maximum specific activity of the pure OPP is 310 FYT/mg of protein [16], this means that the powder contained \(\sim\)0.05% of the active enzyme of the interest. The loss of the specific activity after the spray drying was 8.3%. Biological trials of feed phytase preparations are usually carried out on broilers and pigs. This approach allows a complex analysis of the physiological activity of phytase preparation on carcass parameters; relative weights of visceral organs; meat quality parameters; phosphorous content in excreta [21]; length of the bones [5]; relative yield of the carcass and the meat [20]; physical, mechanical and chemical properties of the tibia; and morphology of the jejunum [30]. These parameters are highly relevant to the practical efficiency of phytase additives; however, using productive animals as a physiological model is resource-intensive--in terms of labour, time and cost. Hence, biological trials using pigs or broilers are rarely used for preliminary trials of enzyme preparations until they are adopted for commercial manufacturing. Using mice for experiments is fast and inexpensive compared with productive animals. This approach is accessible for laboratory-scale testing of the efficiency of phytase preparations as well as other enzyme-containing feed additives. However, there are only a few published examples of using mice for similar purposes [28].