The aim of the study was the evaluation of selected whey proteins susceptability to degradation with proteolytic enzymes isolated from Yarrowia lipolytica yeast. In the research the aspartyl and serine proteases were used for hydrolysis of α-lactoalbumin, β-lactoglobulin and whey protein concentrate (WPC-80). The reaction was carried out at pH 3.0 and pH 8.0 respectively, at 37°C, with the enzyme applied in a dose of 10 U/mg of the protein. The progress of proteolysis was monitored quantitatively by the determination of the hydrolysis degree (DH), free amino groups content and qualitatively by the SDS PAGE electrophoresis and by RP-HPLC. All tested substrates were characterized by low susceptibility to degradation with aspartyl protease, while the application of serine protease caused the intensive degradation mainly β-lactoglobulin.

The object of the study was to determine the effect of the pretreatment of Miscanthus giganteus and straw rape with a 15% solution of ammonia on the availability of polysaccharides in substrates for hydrolysis. Its effectiveness was assessed on the basis of the concentration of reducing sugars released during enzymatic hydrolysis and its efficiency calculated in relation to the total polysaccharides available in materials. Carrying out the pretreatment under conditions of 80°C/6 h resulted in an increase in released sugars concentration by 50% (Miscanthus) and 18% (straw), with regard to the hydrolysis of the materials pretreated under conditions of 20°C/24 h, at the same hydrolysis time. Regardless of the pretreatment variant a higher degree of delignification was reported for Miscanthus than rape straw.

Influence of media components concentration was carried out for the evaluation of biosynthesis of citrate and invertase by Y. lipolytica strain A-101-B56-5 from sucrose as a cheap substrate. The concentration of components was designed in the Design Expert 8 software. All experiments were performer as batch cultures using microtiter plates in Bioscreen C apparatus. Amoung 37 media of different composition (1) the highest amount of biomass (OD_420-580nm = 1.9) was obtained in the medium with high amount of yeast xtract, (2) the highest extracellular invertase activity (63.9 U/l) in the medium with the highest sucrose concentration, (3) the highest concentration of citrate (0.288 g/l) in medium where low concentration of both ammonium chloride and yeast extract were used (the highest carbon to nitrogen ratio – C/N). No common medium was selected for simultaneous biosynthesis of all analyzed products. However, the optimum compositions of media for separate processes were obtained and may be used during biosynthesis of the compounds of interest in the bioreactor cultures using Y. lipolytica A-101-B56-5 strain and sucrose as a cheap substrate.