Abstract
For reducing protein aggregation in foam fractionation, the role of pH-induced structural change in the interface-induced protein aggregation was analyzed using bovine serum albumin (BSA) as a model protein. The results show that the decrease in pH from 7.0 to 3.0 gradually unfolded the BSA structure to increase the molecular size and the relative content of β-sheet and thus reduced the stability of BSA in the aqueous solution. At the isoelectric point (pH 4.7), BSA suffered the lowest level in protein aggregation induced by the gas–liquid interface. In the pH range from 7.0 to 4.7, most BSA aggregates were formed in the defoaming process while in the pH range from 4.7 to 3.0, the BSA aggregates were formed at the gas–liquid interface due to the unfolded BSA structure and they further aggregated to form insoluble ones in the desorption process.
Highlights
Foam fractionation is a physical process in which rising foam serves as the medium to separate surface-active compounds from their diluted solutions [24]
bovine serum albumin (BSA) suffered the lowest level in protein aggregation induced by the gas–liquid interface and no insoluble aggregates were formed in the foamate
As pH deviated from the isoelectric point, the increase in bubble size resulted in the increase in the BSA enrichment ratio
Summary
Foam fractionation is a physical process in which rising foam serves as the medium to separate surface-active compounds from their diluted solutions [24]. Foam fractionation has effectively decreased the price of nisin from 1200 RMB/kg at 2004 to 500 RMB at 2006 and to 300 RMB/kg at 2015 (the data were obtained from Tianjin Kangyi Biotechnology Company). It is presented that protein molecules suffer structural unfolding as they are adsorbed at the gas–liquid interface [1]. In the foam fractionation of proteins, foam drainage is often enhanced to obtain a high enrichment ratio. The enhanced foam drainage reduces the gas–liquid interfacial area to intensify the desorption of adsorbed protein molecules in the rising foam. In this case, protein aggregates will flow into the bulk solution with the drained liquid and may reduce the protein recovery. It is necessary to give a molecular-level understanding of the gas–liquid interface-induced protein aggregation to reduce its bad effect on foam fractionation of proteins
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