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Soluble leaf proteins (SLP) from alfalfa herbage were concentrated by ultrafiltration. Performance of a custom-made rotary ultrafilter with 10 kDa membranes was evaluated with a 2³ factorial experimental design using rotor speed, pressure, and membrane clearance as variables. The device was then operated at various rotor speeds at a given pressure and membrane clearance, and the permeate flux and level of protein concentration were monitored. The applied pressure and rotor speed showed a significant effect in enhancing SLP permeate flux at the beginning of the experiment, but only pressure had a positive effect after 2 h of run time. Rotor speeds showed a detrimental effect on permeate flux by 2 h as well as on protein concentration. The protein concentration in the retentate was only about one-third of the expected theoretical concentration. Egg white proteins (EWP) were also concentrated for comparison. They showed similar protein concentration levels and losses. Performance was also compared with that of a conventional hollow-fiber ultrafiltration device. [ABSTRACT FROM AUTHOR]