Influence of pH and ionic strength on heat-induced formation and rheological properties of cottonseed protein gels

• The effects of pH and NaCl on cottonseed protein isolation (CPI) gel were studied.
• Higher pH values and salt resulted in higher denaturation temperatures.
• NaCl and pH inhibited CPI denaturation resulting in higher gelling points.
• pH and NaCl had effects on determining the structure of networks formed by CPI.

The influence of pH and ionic strength on gel formation and gel properties of cottonseed protein isolation (CPI) was studied using dynamic oscillatory rheometer, differential scanning calorimeter (DSC), and scanning electron microscopy (SEM). The gelation temperature was influenced by ionic strength; salt had a stabilization effect, which inhibited CPI denaturation at higher salt concentrations resulting in higher gelling points. The strongest gel stiffness was made with 0.2 M NaCl. The pH also altered the denaturation temperature of the CPI; higher pH values resulted in higher denaturation temperatures. Maximum gel stiffness occurred at pH 3.8 in 0.5 M NaCl; higher or lower pH values resulted in reduced gel stiffness. The pH and NaCl also played a major role in the structure of gel networks formed by CPI. Lower pH and higher salt concentrations resulted in dense networks. These results are helpful to improve understanding of cottonseed protein, to control aggregation behavior, to improve the quality of cottonseed protein products, and to provide a theoretical base for its development and utilization.