Dynamic oscillatory rheological measurement and thermal properties of pea protein extracted by salt method: Effect of pH and NaCl

The effects of two important factors, pH (3.0-10.0) and NaCl (0-2.0 M), on pea protein gelation properties were studied using dynamic oscillatory rheometer and differential scanning calorimeter (DSC). The strongest gel stiffness was achieved at 0.3 M NaCl; higher or lower salt concentrations lead to weakening of the gel. The gelation temperature was also influenced by ionic strength; salt had a stabilization effect which inhibited pea protein denaturation at higher salt concentrations resulting in higher gelling points (p<0.05). At a NaCl concentration 2.0 M, pea protein gelation was completely suppressed at temperatures <= 100 degrees C. The pH also played an important role in gel formation by pea protein isolates since acid and base cause partial or even total protein denaturation. In this paper the maximum gel stiffness occurred at pH 4.0 in 0.3 M NaCl; higher or lower pH values resulted in reduced gel stiffness (p<0.05). pH also altered the denaturation temperature of the pea protein; higher pH values resulted in higher denaturation temperatures and higher enthalpies of denaturation (p<0.05). At pH 3 pea proteins seem like completely denatured by acid as the DSC curve showed a straight line. The gelation temperature (gelling point) peaked at pH similar to 6.0 (89.1 degrees C). Careful adjustment of pH and NaCl concentration would enable the food industry to effectively utilize the salt-extracted pea protein isolate as a gelling agent. (C) 2011 Elsevier Ltd. All rights reserved.