Synergistic effect of pH shifting and mild heating in improving heat induced gel properties of peanut protein isolate

Peanut protein isolate (PPI) was first subjected to pH shifting treatment at pH 7 or pH 10 with temperatures ranging from 25 degrees C to 70 degrees C. Then the structure and heat induced gel properties of PPI were investigated. The breaking force and water holding capacity of PPI10-40 (PPI after pH shifting with pH 10 at 40 degrees C) gel were 2.2 times and 2.15 times that of PPI7-25. Moreover, they were higher (p = 0.001637, p = 0.000916, p = 0.000021, p = 0.23) than that PPI7-40 or PPI10-25, indicating the synergistic effect of pH shifting and mild heating in improving the gel properties of PPI. These results were probably because the particle size of PPI10-40 decreased was 1.8 times that of PPI7-25 measured from DLS. Moreover, the solubility, free sulfhydryl content and surface hydrophobicity of PPI10-40 were 1.3 times, 1.8 times and 1.6 times that of PPI7-25 respectively, which resulted in enhanced covalent or non-covalent interactions between proteins. Circular dichroism and intrinsic fluorescence spectroscopy suggested that both heating and pH shifting significantly changed the secondary and tertiary structure of PPI. So the combined treatment of pH-shifting and mild heating is an efficient method to improve the gel properties of PPI (PPI10-40) to the maximum extent.