Increase of bubble size playing a critical role in foam-induced protein aggregation: Aggregation of BSA in foam fractionation

- Increase of bubble size enhanced desorption of BSA to induce its aggregation.
- Drainage promoted increase of bubble size to enhance the aggregation of BSA.
- Drainage also enhanced the formation of aggregates with larger size.
- The aggregation of BSA occurred in the rising foam and the defoaming process.
- Foam-induced protein aggregation greatly reduced the separation performances.

In this work, the role of increase of bubble size in foam-induced protein aggregation was investigated using bovine serum albumin (BSA) as a model protein. Firstly, different increases of bubble size were obtained by varying the height of rising foam. Then, the effects of increase of bubble size on the desorption of BSA molecules from the interface, and the aggregation of desorbed BSA molecules in the rising foam and during the defoaming process were studied. Finally, the effects of the foam-induced aggregation on the performances of foam fractionation of BSA were studied. The results show that by reducing the flux of the gas-liquid interfacial area, the increase of bubble size desorbed BSA molecules from the interface to cause protein aggregation. By promoting the increase of bubble size, foam drainage intensified the foam-induced BSA aggregation, and increased the production of BSA aggregates with larger-sizes. For a slight increase in bubble size, most of the BSA aggregates were produced during the defoaming process, so both the enrichment ratio and recovery percentage of BSA monomer reduced. Whereas for more significant increase of bubble size, most of the BSA aggregates were produced in the rising foam and companied with enhanced foam drainage, they decreased both the recovery percentages of BSA overall and BSA monomer.