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Effects of added yeast on protein transmission and flux in cross-flow membrane microfiltration
1Department of Chemical Engineering, University of Colorado, Boulder, Colorado 80309-0424, USA.
Abstract:
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.
Insights
Adding yeast cells to microfiltration significantly improves protein recovery. Yeast cells form a protective layer, enhancing protein transmission and reducing membrane fouling compared to protein-only solutions.
Area of Science:
- Biochemical Engineering
- Separation Science
- Membrane Technology
Background:
- Microfiltration membranes are crucial for separating proteins but suffer from fouling, reducing efficiency.
- Protein fouling, particularly with bovine serum albumin (BSA), leads to decreased flux and transmission.
- Understanding fouling mechanisms is key to optimizing protein recovery processes.
Purpose of the Study:
- To investigate the impact of yeast cells on microfiltration performance, specifically flux and protein transmission.
- To compare microfiltration of bovine serum albumin (BSA) solutions with and without yeast cells.
- To evaluate the role of yeast cell concentration in protein recovery.
Main Methods:
- Cross-flow microfiltration experiments were conducted using BSA as a model protein.
- Experiments were performed with BSA-only solutions and BSA-yeast cell mixtures.
- Flux, protein transmission, and protein recovery were measured over time.
Main Results:
- BSA-only microfiltration formed a fouling layer, limiting BSA transmission to 25-40%.
- Microfiltration with yeast cells resulted in a dynamic cake layer, enhancing BSA transmission to 60-90%.
- Yeast addition at low concentrations (<1 g/L) increased BSA recovery by 50-100% compared to BSA-only solutions.
Conclusions:
- Yeast cells act as a dynamic membrane, preventing protein fouling and improving protein transmission during microfiltration.
- The presence of yeast cells significantly enhances protein recovery, especially at lower yeast concentrations.
- Optimizing yeast concentration is important for balancing high protein transmission and acceptable flux rates.