Rheological characterization of thermal gelation of cowpea protein isolates: Effect of processing conditions

Abstract

Processing conditions such as protein concentration, maximum temperature, heating and cooling rates were analyzed for gelation of untreated (A8) and pH-shifting-modified (A10) cowpea protein isolates. Rheological measurements allowed characterization of finished gels as well as deeper understanding of gelling process. During thermal cycle, gelation started with a low denaturation degree, which reflects a good ability of cowpea proteins to interact with themselves and water. Gels were obtained at temperatures as low as 70 °C, a low temperature in the context of plant proteins. pH-shifting was a simple and inexpensive way to improve gel forming ability in terms of stiffness (G′) and minimum protein concentration and temperature required. Maximum temperature conditioned G′ and viscoelasticity (tan δ). Gels formed by A10 with treatments at 70–80 °C were more elastic than A8 ones, but differences were canceled when gels were formed at 90–95 °C. The highest increase of G′ occurred during cooling stage, which suggests a great contribution of hydrogen bonds. However, A10 gels had a greater contribution of heat-induced interactions, probably hydrophobic, than A8 gels, when thermal treatments were at 70–80 °C. The versatile gelling ability of cowpea protein isolates represents a way to introduce them as a replacement for animal proteins.