Precipitation of proteins from soybean whey wastewater by successive foaming and defoaming

Abstract

To remove whey soybean proteins (WSP) from soybean whey wastewater (SWW), a continuous technology of successive foaming and defoaming was developed to precipitate WSP based on the foam fractionation of WSP from SWW. The roles of foaming and elevated temperature in precipitation of WSP were firstly investigated. The results show that foaming played the critical role in the precipitation of WSP, particularly the precipitation of lipoxidase, β-amylase and lectin, and elevating temperature enhanced the foaming-induced precipitation. Based on these results, the technology was optimized by studying the effects of temperature, pore diameter of gas distributor, superficial air flowrate and retention time on the removal yield of WSP. Under the conditions of length of foam column 700 mm, temperature 60.0 °C, pore diameter of gas distributor 120 ± 20 μm, superficial air flowrate 2.55 mm/s and retention time of 5.0 h, a high removal yield of 88.4 ± 3.9% was obtained. A SDS-PAGE analysis of the variation of WSP composition with retention time further confirmed the effective removal of WSP from SWW, and lectin was found to be the only soluble protein in the residual SWW. Compared with batch foam fractionation, the current technology was more effective in separating WSP from SWW.