Synthesis of carboxymethyl flaxseed gum and study of nonlinear rheological properties of its solutions

Flaxseed gum (FG) was carboxymethylated by reacting it with monochloroacetic acid (MCA). The effects of concentrations of NaOH and MCA, reaction temperature and reaction time, on the degree of substitution (DS) were investigated. Reaction between the FG and MCA at NaOH and MCA concentrations of 0.06 g/mL and 0.08 g/mL, respectively, at 70 °C for 60 min produced carboxymethyl flaxseed gum (CMFG) with a DS of 0.969. Carboxymethylation of FG increased its solubility and light transmittance in water. The nonlinear rheological properties of CMFG solutions were studied using large amplitude oscillatory shear (LAOS) tests, Fourier transform (FT) rheology and Chebyshev stress decomposition methods. The different nonlinear rheological behaviors observed were related to the microstructures of the CMFG solutions as a function of concentration and DS.