Expanded bed adsorption of human serum albumin from very dense Saccharomyces cerevisiae suspensions on fluoride-modified zirconia

The adsorption of proteins from high cell density yeast suspensions on mixe d-mode fluoride-modified zirconia (FmZr) particles (38 to 75 mu m, surface area of 29 m(2)/g and density of 2.8 g/cm(3)) was investigated using human serum albumin (HSA) added to Saccharomyces cerevesiae as the model expressi on host. Because of the high density of the porous zirconia particles, HSA (4 mg/ mt) can be adsorbed from a 100 g dry cell weight (DCW)/L yeast suspe nsion in a threefold-expanded bed of FmZr. The expanded bed adsorption of a ny protein from a suspension containing >50 g DCW/L cells has not been prev iously reported. The FmZr bed expansion characteristics were well represent ed by the Richardson-Zaki correlation with a particle terminal velocity of 3.1 mm/s and a bed expansion index of 5.4. Expanded bed hydrodynamics were investigated as a function of bed expansion using residence time distributi on studies with sodium nitrite as the tracer. The adsorption of HSA on FmZr exhibited features of multicomponent adsorption due to the presence of dim ers. The protein binding capacity at 5% breakthrough decreased from 22 mg H SA/mL settled bed void volume for 20 g DCW/L yeast to 15 mg HSA/mL settled bed void volume for 40 g DCW/L yeast and remained unchanged for the higher yeast concentrations (60 to 100 g DCW/L). However, the batch (or equilibriu m) binding capacity decreased monotonically as a function of yeast concentr ation (20 to 100 g DCW/L) and the binding capacity at 100 g DCW/L yeast was fivefold lower compared with that at 20 g DCW/L yeast. The lower batch bin ding capacity at high cell concentrations resulted from the adsorption of c ells at the surface of the particles restricting access of HSA to the intra particle surface area. Batch (or equilibrium) and column HSA adsorption res ults indicated that the adsorption of HSA on FmZr occurred at a time scale that may be much faster than that of yeast cells. The zirconia particles we re cleaned of adsorbed HSA and yeast with a total of 1500 to 2000 column vo lumes lover many cycles) of 0.25 M NaOH, without any significant effect on the chromtographic performance. (C) 1999 John Wiley & Sons, Inc.