Fractionation of lysozyme and chicken egg albumin using ultrafiltration with 30-kDa commercial membranes

Lysozyme is an important protein in chicken egg white (CEW) and it is feasible to separate lysozyme from other CEW proteins using ultrafiltration. To identify suitable conditions for the fractionation of lysozyme from CEW, we studied with the model binary mixture of lysozyme and chicken egg albumin (CEA) with the composition and concentration of the two proteins similar to those in natural CEW. Two commercial ultrafiltration (UF) membranes of 30-kDa molecular weight cutoff (MWCO) made of regenerated cellulose (RC) and poly(ether sulfone) (PES) membranes were used. By systematically examining the effect of the physicochemical properties of the solution and the hydrodynamics of the membrane systems, the most suitable conditions to achieve maximum transmission and selectivity for lysozyme were identified. The PES UF membranes offer distinct advantages for the fractionation of lysozyme from this binary mixture. With the 30-kDa PES UF membrane, the suitable conditions were identified as pH 10-11, salt concentration (NaCl) 100 mM, permeate flux 26.5 L/m(2) h, and stirring speed 2100 rpm. Under these conditions, a lysozyme transmission of 99% was obtained and the selectivity of separation was as high as 2400.