Protein Recovery in Aqueous Extraction Processing of Soybeans Using Isoelectric Precipitation and Nanofiltration

Abstract

AbstractIsoelectric precipitation and whey nanofiltration were evaluated in recovering protein from skim fractions produced by enzyme‐assisted aqueous extraction processing (EAEP) of extruded full‐fat soybean flakes. Countercurrent two‐stage EAEP was performed at 1:6 solids‐to‐liquid ratio, 50 °C, pH 9.0, and 120 rpm for 1 h to extract oil and protein from soybeans. Two protein recovery strategies were applied to skim fractions produced by different extraction treatments: Treatment 1 using 0.5% protease (wt/g extruded flakes) in both extraction stages; Treatment 2 using 0.5% protease only in the 2nd extraction stage; and Treatment 3 using no enzyme in either extraction stage. Protein recovery by using isoelectric precipitation was inversely related to the extent of hydrolysis with recoveries of 27, 61, and 87% of skim proteins from Treatments 1, 2, and 3, respectively. Overall protein recoveries of 26, 54, and 57% of the original protein in the extruded full‐fat flakes were achieved when combining extraction treatments and isoelectric precipitation. Nanofiltering isoelectric wheys (500‐Da membrane) achieved protein retentate yields of 96.3, 94.5, and 91.8% (1.9–2.8 concentration factor) with permeate fluxes up to 1.35 kg/h m2. About 97, 98, and 99% of skim protein were recovered by isoelectric precipitation and whey nanofiltration for Treatments 1, 2, and 3, respectively. Overall protein recoveries of 93, 87, and 65% of the protein in the extruded flakes were achieved for Treatments 1, 2, and 3, respectively. Although high protein retentions were achieved, very low permeate fluxes were observed for whey nanofiltration.