Nanoreduction of Millet Proteins: Effect on Structural and Functional Properties

In this study, proteins from three different millet varieties, viz., sorghum (SP), pearl millet (PP), and foxtail millet (FP), were obtained using the isoelectric precipitation method and nanoreduced using ultrasonication treatment. The aim of the study was to investigate the effect of nanoreduction on the protein structural, functional, and thermal attributes. The mean particle sizes were found to be 335.40, 587.98, and 801.42 nm for pearl millet protein nanoparticles (PPU), foxtail protein nanoparticles (FPU), and sorghum protein nanoparticles (SPU). An increased ζ potential (from −11.25 to −15.87) for nanoprotein samples revealed their increased stability. A sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) profile revealed a significant reduction in molecular weight (27–10 kDa) following nanoreduction. Moreover, nanoprotein samples revealed improved functional attributes like solubility, emulsifying, foaming, and hydrophobicity with decreased turbidity. Scanning electron microscopy (SEM) revealed disorientation in the microstructure of protein after nanoreduction. An alteration in functional groups and conformational attributes of proteins after sonication was measured using Fourier transform infra-spectroscopy (ATR-FTIR) and X-ray diffraction (XRD) analysis. Differential scanning calorimetry (DSC) showed a significant reduction in denaturation temperatures (50–65 °C) and enthalpy (5.5–7.0 J/g) of proteins after nanoreduction. This work highlights that ultrasound can successfully produce protein nanoparticles with improved function, structural, and thermal attributes.