Effect of ultrasound on pH-shift to improve thermal stability of coconut milk by modifying physicochemical properties of coconut milk protein

Abstract

In this study, ultrasound was subjected to pH-shift treatment to explore their synergistic effects on thermal stability of coconut milk and the underlying mechanism was explored by investigating the changes in functional properties and structures of coconut milk protein. The results showed that ultrasound combined with alkaline pH-shift treatment improved the viscosity (from 239.5 to 309.2 mPa), increased zeta potential (from −22.3 to −24.8 mV) and decreased the size distribution curve right shift distance (from 4.07 to 2.15 μm) of coconut milk compared to alkaline pH-shift treatment alone. This was future elucidated by the enhance effect of ultrasound assisted alkaline pH-shift to improve physicochemical properties of coconut milk protein, including higher solubility (from 43.4% to 51.8%), higher surface hydrophobicity (from 5877.2 to 13372.7) and fewer free sulfhydryl group (from 441.8 to 352.5 μmol/g). The improved properties were consistent with changes in the secondary structure, tertiary structure and microscopic state of coconut globin reflected by the fourier transform infrared spectroscopy, fluorescence spectroscopy and scanning electron microscopy, respectively. In conclusion, ultrasound can amplify the effect of pH-shift on increasing the thermal stability of coconut milk by modifying functional properties and structures of coconut milk protein, especially under alkaline pH-shift treatment.