Role of foam drainage in producing protein aggregates in foam fractionation

Ascertainment of Surfactin Concentration in Bubbles and Foam Column Operated in Semi-Batch

This paper describes a mathematical model for the convection, diffusion, and balance phenomena for predicting the depletion curves, i.e., variations in the timed surface-active molecule concentration for fractionation processes in bubbles and foam column, operated in semi-batch. The model was applied for the purification of the surfactin solution and the results were compared with experimental data. Gibbs adsorption curves were obtained for the biosurfactant at different temperatures, and then adjusted with estimated parameters, according to the Langmuir adsorption model. The gas bubble sizes were optically determined. The isotherm adsorption parameters and bubble average diameter are crucial for the attainment of the depletion curves, generated by the model described. The results demonstrate that the process is most effective when operating a column with reduced gas flow and low initial concentration. A top product with two or thirty times greater concentration than the initial one was achieved and the highest biosurfactant concentrations were attained for higher operating temperatures. It was also observed that bubble diameter increased with a higher gas flow. The adjustment obtained for the adsorption curves of Gibbs was satisfactory. Therefore, there was evidence that surfactin molecules adsorb in monolayers in the liquid–gas interface.

Effects of nanobubbles on peptide self-assembly

It is believed that the aggregation of amyloid proteins or peptides is promoted by the presence of an air-water interface, and substantial evidence suggests that the characteristics of the air-water interface play critical roles in foam-induced protein aggregation during foam fractionation. However, the effects of the air-water interface on the self-assembly of amyloid-like peptides have not yet been elucidated clearly at the nanometer scale. In this work, air nanobubbles produced in water solution were employed for studying interfacial effects on the self-assembly of a model amyloid peptide termed P11. An atomic force microscopy study showed that the air nanobubbles induced the formation of peptide fibrils with a 9-13 nm helix structure in the P11 solution. Thioflavin T fluorescence and circular dichroism spectroscopic analysis indicated that the nanobubbles induced the change of the peptide conformation to a β-sheet structure. Based on these observations, we have proposed a mechanism to explain how the nanobubbles affect the self-assembly of the P11 peptide at the nanometer scale. Since air nanobubbles are present in water solutions in addition to an air-water interface in normal experiments in vitro, our results indicate that nanobubbles must be taken into account to achieve a complete understanding of protein aggregation events.