Molecular mechanism underlying the effects of temperature and pH on the size and surface charge of octenylsuccinated oat β-glucan aggregates.

• Surface tension, size and ζ of OS β G aggregates induced by temperature/pH were probed. • Compactness of hydrophobic and hydrophilic domains was both temperature/pH dependent. • Balance of different molecular interactions confirmed OS β G aggregates structure. • The aggregate formation for OS β G was driven collectively by enthalpy and entropy. • Transition mechanism of OS β G aggregates induced by pH and temperature was established. Environmental temperature and pH induced significant changes in the size and surface charge (ζ) of octenylsuccinated oat β -glucan aggregates. The underlying mechanisms were explored by using 1H-NMR, fluorescence spectra, thermodynamic analysis, and SAXS. At pH 6.5, the size decreased with temperature while ζ continuously increased. With increasing pH at 293 K, parabolic and U-shaped trends were observed in the size and ζ , peaking at pH 8.5 and 6.5, respectively. At any tested pH, the size decreased with temperature. Overall, ζ significantly increased with temperature at each pH. As temperature increased, the compactness of hydrophobic-domains increased while the compactness of hydrophilic-domains decreased. In an acidic environment, both the compactness increased with decreasing pH, but in an alkaline environment, they decreased with pH. The compactness changes were co-driven by enthalpy and entropy and corresponded to changes in the hydrophobic interactions in hydrophobic-domains, hydrogen bonds in hydrophilic-domains and electrostatic repulsions among octenylsuccinate molecules. [ABSTRACT FROM AUTHOR]