Formation and pH-stability of whey protein fibrils in the presence of lecithin
Raphaela Araujo Mantovani, Juliana Fattori, Mariano Michelon, Rosiane Lopes Cunha
The effect of the soybean lecithin (SL) (0–0.25% w/v) on the kinetics of whey protein (2% w/v) fibrils formation and their stability under different pH values were evaluated. Linear and long fibrils were formed in the presence of SL at concentrations below critical micelle concentration whilst a higher SL content led to fibrils aggregation. The electrophoretic profiles and rate of fibril formation were not affected by the presence of SL. In spite of indicating SL-protein interaction, circular dichroism results showed that SL did not affect significantly the protein secondary structure conformation during heating. The pH-stability of fibrils was evaluated in a pH range from 3 to 7. At pH 3, the fibrils were isolated, but the increase of pH to 5 led to the formation of big aggregates that became more opened at pH 7, mainly in the presence of SL. These results were confirmed by small-angle X-ray scattering profiles. Different from fibrils formed without SL, the secondary structure of fibrils formed in the presence of SL showed no differences increasing pH from 3 to 7. Thus, despite not affecting the fibril growth mechanism and conformation, the presence of SL decreased the protein susceptibility to pH changes broadening the potential application of nanofibrils as a food ingredient. In this context, changes of process variables were carried out in order to enhance whey protein nanofibril formation in the presence of lecithin. Alternatives such as increasing pH, reducing protein-lecithin ratio and the modification of phospholipids composition favored the amyloid-like structure formation.
Circular dichroism, Secondary structure, Protein denaturation, Protein folding, Aggregation, Food science, Biochemistry