Constant permeate flux microfiltration of liquid whey protein concentrate for the separation of whey proteins from fat

Abstract Text: Value added whey protein concentrates (WPC) are often processed by membrane filtration to fractionate valuable components. One such application is microfiltration (MF) applied to cheese whey to separate proteins from fats before the protein-rich fraction can be further concentrated into products containing > 80% (wt/wt) total nitrogen on a dry basis. The objective of this research was to evaluate protein recovery into permeate during MF of reconstituted WPC 50% protein on a dry basis by using constant permeate flux (CF) operation, compared to conventional constant pressure (CP) operation. Typically, MF are started and operated at low (e.g. 27 to 138 kPa) and constant pressures (baseline and differential), which could affect the long term fouling and throughput of the filter. An alternative is to maintain a constant permeate flux by modulating applied pressure during MF to modify the initial fouling, hopefully increasing protein permeation and recovery. Approximately 400 kg of liquid WPC 50% (10% solids) was made by mixing whey permeate, pure water, and liquid WPC 80%. A 200 kg aliquot was MF (0.5 µm, 6.0× mass concentration factor, 150% water diafiltration [wt/wt on a feed mass basis], 60°F) using either CP or CF operation. This was replicated three times, using different lots of WPC 50% for each replicate. During CF MF, flux (L/m² per h) was initially controlled by adjusting a permeate outlet valve to achieve the desired flow. As product in the recirculation loop became concentrated, flux was maintained by opening the permeate valve, then increasing the differential pressure, and thus inlet pressure. Pressures during CP MF were maintained at 27.6 kPa baseline, and 82.7 kPa differential, giving an inlet of 110.3 kPa. Inlet pressure during CF MF increased to 172.4 kPa when the solids in the recirculation loop increased, whereas baseline pressure remained steady at 27.6 kPa. Protein (total nitrogen) recovery from feed into permeate was 63.2 ± 1.1 and 71.8 ± 4.4% for CP and CF MF, respectively. Average permeate flux during MF was 19.4 ± 3.7 and 17.4 ± 3.2 L/m² per h, for CP and CF MF, respectively. These results indicate that CF operation during whey MF can increase the amount of protein recovered, without greatly affecting throughput of the filtration. This research could help whey processors improve the efficiency and value of their products by implementing relatively minor changes to their processes.

Keywords: whey, microfiltration, constant permeate flux