Ultrasound and high-speed shear pretreatments of walnut meal protein: Structural and functional characterization and mechanistic investigation

The study aims to investigate the effect of the addition of ultrasound (US) with high-speed shear (HSS) at the extraction stage on the yield, physicochemical, structural, and functional properties of walnut meal protein (WMP). Compared with the conventional alkaline soluble acid precipitation method, the WMP yields after US and HSS pretreatments were increased by 1.11 and 1.21 times, respectively. Protein samples treated with the US showed increased surface hydrophobicity, a more uniform distribution of particle sizes, and greater contact angles. SDS-PAGE results showed that the protein had broken peptide bonds at higher molecular weights. The proteins' free sulfhydryl groups and fluorescence intensity have both increased as a result of the two pretreatment approaches, indicating a substantial alteration in the proteins' tertiary structure. Dynamic light scattering and SEM findings revealed that the US and HSS treatments improved the protein water solubility and emulsion stability by reducing the aggregate particle size and homogenizing the protein dispersion system. These results indicate that US and HSS pretreatment can effectively solubilize WMP polymers and enhance the structural function of the protein. This provides a theoretical basis for the application of WMP in food processing and offers a suitable technology for improving protein utilization.