Impact of pH-shift processing combined with ultrasonication on structural and functional properties of proteins isolated from rainbow trout by-products

The effects of alkaline and acid solubilization pHs (11, 11.5, 3.5 and 2.5) combined with ultrasonication (100, and 400 W for 0, 5, 10 and 20 min) on protein recovery from rainbow trout by-product and its structural and functional properties were investigated. The combination of pH-shift processing with ultrasonication increased protein solubilization and total yield compared with the classic pH-shift processing. The combination also significantly reduced particle size, tryptophan fluorescence intensity, and reactive sulfhydryl groups content of the protein isolates. The secondary structure of the proteins was also influenced by ultrasonication with decreasing in α-helix and increasing in β-sheet, β-turn and random coil content. However, SDS-PAGE demonstrated no difference in the molar masses of the proteins. Emulsifying and foaming properties of the proteins improved by applying the combined method. However, the level of improvements was governed by solubilization pH as well as ultrasound exposure power and time. Altogether, pH-shift processing combined with ultrasonication increased protein recovery from the fish by-products while the structural changes induced with the combination improved functional properties of the recovered proteins.