The effectiveness of ultrafiltration for the purification of recombinant proteins from aqueous corn endosperm and germ extracts was examined using model proteins of two different sizes, recombinant type I human collagen (rCollagen, 265 kDa) and green fluorescent protein (GFP, 27 kDa), to evaluate the effects of membrane pore size, transmembrane pressure (TMP), crossflow rate, and filtration pH on permeate flux and protein sieving. Using a 300 kDa MWCO membrane resulted in a significant loss of rCollagen, whereas a 100 kDa MWCO membrane completely retained rCollagen. Increasing the filtration crossflow rate and TMP resulted in a higher permeate flux without significantly altering the sieving of the host cell proteins (HCP) or GFP. The greatest HCP sieving was observed in the endosperm extract filtration at low pH and, compared to endosperm, the filtration of germ extracts had lower HCP sieving. GFP exhibited similar sieving as the average HCP for all filtration conditions. rCollagen purity of 89% was achieved with only diafiltration of endosperm extracts and, when preceded by precipitation, a purity of >99% was attained. Thus, ultrafiltration is a valuable method to separate and purify corn-hosted recombinant proteins >100 kDa, particularly when the expression is targeted to the endosperm. (C) 2010 Elsevier B.V. All rights reserved.