Structure conformational and rheological characterisation of alfalfa seed (Medicago sativa L.) galactomannan

In the present work a galactomannan extract of low protein residue (< 1.3 % wt dry basis) was isolated from alfalfa (Medicago sativa L.) seed endosperm meal. The alfalfa gum (AAG) comprised primarily mannose and galactose at a ratio of 1.18:1, had a molecular weight of 2 x 10(6) Da and a radius of gyration of 48.7 nm. The average intrinsic viscosity of the dilute AAG dispersions calculated using the modified Mark-Houwink, Huggins and Kraemer equations was 9.33 dLg(-1) at 25 degrees C. The critical overlap concentration was estimated at 0.306 % whereas the concentration dependence of specific viscosity for the dilute and semi-dilute regimes was proportional to C-2.3 and C-4.2, respectively. The compliance to the Cox-Merz rule was satisfied at 1% of AAG, whereas a departure from superimposition was observed at higher concentrations. Viscoelasticity measurements demonstrated that AAG dispersions exhibit a predominant viscous character at 1 % wt, whereas a weak gel-like behaviour was reached at AAG concentrations >= 3 %.

Automated summary

A galactomannan extract of low protein residue was isolated from alfalfa seed endosperm meal, with mannose and galactose as the primary components. The intrinsic viscosity of dilute AAG dispersions was calculated, and viscosity behavior varied with concentration, showing both viscous and gel-like properties.