Isolation and rheological characterization of Mucuna flagellipes seed gum

The gum from Mucuna flagellipes seed endosperm has been isolated and characterised using capillary viscometry and steady shear and small deformation oscillatory rheometry. The endosperm was found to constitute 67.15% of the whole seed and yielded 32.6% of gum. The Huggins and Kraemer plots obtained by capillary viscometry gave an intrinsic viscosity of 7.9 dL/g and viscosity average molecular mass was calculated to be 2.1 x 10(6) using the Mark-Houwink relationship. The zero shear viscosity was plotted against the coil overlap parameter, C[eta], and the slopes of the lines in the dilute and semi-dilute regions were found to be similar to 1.0 and 4.6 respectively. The curves were fitted to the Tuinier and Martin equations and showed only qualitative agreement. The shear flow viscosity profiles indicated that M. flagellipes gum did not exhibit significant shear thinning at polymer concentrations less than 0.5%, however, at higher concentrations, pronounced shear thinning was observed with the relaxation time (tau) increasing with increase in polymer concentration. The dynamic viscosity profiles showed that at all polymer concentrations examined, a Newtonian plateau was obtained at low frequencies indicating that the loss modulus was the dominant response. Plots of log eta versus log (gamma) over dot and log eta* versus log omega were not superimposible and hence did not obey the Cox-Merz rule. (C) 2008 Elsevier Ltd. All rights reserved.