Functionalizing cottonseed protein by sequential pH-shifting and ultrasonication

The physicochemical, functional, rheological, conformational, and thermal attributes of cottonseed meal protein (CMP) prepared by pH-shifting and/or ultrasonication were investigated. CMP isolates were altered using acidic (pH 1.5, 3.5) or alkaline (pH 9.5, 11.5) treatments followed by ultrasonication before neutralization. Traditionally extracted CMP was used as native protein (control). Sequential pH 11.5-shifting and cavitation was the most effective treatment in decreasing particle size, turbidity, and wetting time of CMP, while increasing protein dispersibility and emulsion stability index. Synergistic treatments (i.e., pH-shifting/sonication) substantially impaired viscosity and viscoelastic characteristics compared to control and pH-shifting counterparts, illustrating the collapse of polymeric chains and inter-molecular hydrogen bonds in CMP. SDS-PAGE revealed that, relative to control or alkaline treatments, pH 1.5 and 3.5-treated CMP isolates showed lighter-intensity subunits at lower molecular weights (12-19 kDa), suggesting the development of large aggregates under acidic conditions. Moreover, intrinsic fluorescence, X-ray diffraction spectra, and DSC thermograms showed that CMP isolates modified with sonication-aided alkaline pHs-treatment had a more flexible tertiary conformation, along with lower crystallinity, rigidity, and thermostability than control or other samples. The current outcomes offer an effective strategy to modify the functionality and rheological characteristics of CMP isolate for application as a building-block in food formulations.