pH-shifting and sonication synergistically altered cottonseed protein: Correlating the conformational and functional characteristics

Abstract

pH-shifting (pH 1.5, 3.5, 9.5, 11.5) and sonication were exclusively and synergistically used to produce cottonseed meal protein (CSMP) with modified structure and improved functionality. Conventionally extracted CSMP served as control. Combined pH-shifting and sonication considerably reduced the β-sheet (40 – 27 %), but increased random coil (12 – 34 %) and β-turn (25 – 35 %) content of CSMP, suggesting partial unfolding in the secondary structure of the protein. From scanning electron microscopy and UV-VS spectroscopy data, the synergistic use of alkaline pH-shifting and ultrasonication resulted in the production of CSMP that had disintegrated microstructure and smaller particle sizing, with higher peak absorption, compared with the control; indicating the collapse of intramolecular hydrogen bonds and interactive forces among CSMP molecules. Further, pH-shifting and/or ultrasonication remarkably strengthened sulfhydryl clusters and surface hydrophobicity, but decreased the disulfide bonds and lightness of CSMP. Most importantly, combined treatment at alkaline conditions increased absolute surface charge, solubility, foamability, and oil binding efficacy over control, and pH-shifting alone (p < 0.05). Contrarily, CSMP isolates modified with sequential treatment displayed a reduction in foaming stability (supported by foaming morphology) and water holding efficacy. Overall, the findings indicated that synergistic pH-shifting/sonication may help increase the utilization of CSMP in the development of new food ingredients.