Beta-Galactosidase Retention by Hollow Fiber Membranes

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Abstract
The method of loading Aspergillus oryzae .beta.-galactosidase [an enzyme useful for lactose hydrolysis in the dairy foods industry] in a hollow fiber membrane unit influenced both enzyme retention and loss of activity during operation. Operated in the normal ultrafiltration mode with enzyme in the recirculating retentate, there was $ 5% leakage across the membrane and .apprx. 50% loss of enzymatic activity after 2 h. Loading enzyme in the sponge layer of the membrane markedly increased leakage across the membrane, but there was minimal loss of activity (< 10%) of the enzyme retained. Average leakage was 30, 40 and 7% when the membrane reactors were run in the recycle, backflush and static modes. Leakage of enzyme across the membrane was not related to a change in molecular weight (100,000 daltons) of the enzyme nor to defects in the membrane. Results of enzyme retention cannot be explained by the lumen pore size theory. Therefore, a dynamic membrane theory is proposed that states that synthetic membranes are dynamic structures whose molecular size exclusion can be influenced by a combination of variables including flux, flow, solvent, solute and membrane polymer type.