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Effects of Added Yeast on Protein Transmission and Flux in Cross‐Flow Membrane Microfiltration

Microfiltration membranes may be used to separate valuable proteins from suspensions containing cells or cell debris. Although a clean microfiltration membrane allows for complete protein transmission and high flux, both of these quantities decline in time due to membrane fouling. Using bovine serum albumin (BSA) as a model protein, flux and protein transmission during cross‐flow microfiltration were studied with and without added yeast cells. Cross‐flow microfiltration of BSA‐only solutions results in a BSA fouling layer with low permeability forming on the membrane surface. Due to this layer, the long‐term BSA transmission is typically only 25–40%. In contrast, during microfiltration of yeast−BSA mixtures, the yeast forms a cake layer on the membrane surface. The yeast cake acts as a dynamic or secondary membrane, allowing BSA monomers to pass through but preventing protein aggregates from fouling the membrane. The result is slower flux decline and higher long‐term BSA transmission of typically 60–90%. For filtration of yeast−BSA mixtures at low yeast concentrations (<1 g/L), 50–100% higher BSA recovery is obtained than for BSA‐only solutions with the same BSA concentration. At high yeast concentrations (>5 g/L), the protein transmission remains high, but the recovery may be lower due to reduced flux.