Recovery of soluble white proteins from discarded brown juice of lucerne biorefinery by integrating foam separation and aqueous two-phase extraction

Lucerne (Medicago sativa L.) is acknowledged as an important biomass feedstock for bioethanol production. However, the by-products of lucerne biorefinery may lead to environmental burdens, especially the deproteinzed effluent (brown juice). In this work, an integrating technology of foam separation and aqueous two-phase extraction was developed to recover soluble white proteins (SWP) from discarded brown juice. First, foam separation was used to isolate SWP from discarded brown juice. Under the optimal operating conditions obtained by response surface methodology (RSM), enrichment ratio (E) and recovery percentage (R) of SWP were 2.96 ± 0.17 and 97.85 ± 1.87%, respectively. In order to overcome the paradox between E and R, the foamate had been prepared into aqueous two-phase system (ATPS) using PEG and (NH₄)₂SO₄. The suitable molar mass of PEG and pH were 2000 and 6.5, respectively. When PEG-(NH₄)₂SO₄ mass ratio was 0.54, the partition coefficient of SWP in ATPS reached 4.21 ± 0.11. Subsequently, foam separation was conducted once again by using above ATPS as the feeding solution. Under the optimal operating conditions, E and R of SWP were 10.47 ± 0.25 and 93.58 ± 1.64%, respectively. The total E and R of SWP from the integrating technology of foam separation and aqueous two-phase extraction were 31.21 ± 3.80 and 91.57 ± 3.32%, respectively.