Structure conformational, physicochemical and rheological characterisation of red clover seed (Trifolium pratense L.) galactomannan

In the present work, a galactomannan isolated from the endosperm of red clover (Trifolium pratense L.) seeds was studied for its feasibility as a thickening and gelling agent in food applications. Red clover seed galactomannan (RCG) had a mannose-to-galactose ratio of 1.12, a molecular weight of 1500 kDa (SEC-MALS) and an intrinsic viscosity of 13.6 dL g⁻¹. The solvation affinity of RCG in water was equivalent to θ-solvent, according to the estimated Kraemer and Huggins coefficients. The critical coil overlap concentration of the RCG solutions in water was estimated to be c∗ = 0.35 wt %, whereas the concentration dependence of specific viscosity in the dilute and semi-dilute regimes was ∝ c^2.3 and c^4.2, respectively. The water vapour sorption dynamics of RCG were controlled by a solution-like sorption mechanism. RCG exhibited a semi-crystalline structure with the glass transition occurring at T_g,onset ≈ 44 °C. The viscoelastic behaviour of the RCG solutions (1–7 wt %) obeyed the concentration superposition principle with a breakpoint in the relaxation dynamics to occur at c ≈ 2 wt %. A time-temperature-concentration super master curve was successfully constructed for c ≥ 2 wt % and temperatures between 5 and 65 °C with an Arrhenius kinetics calculated activation energy of 23.5 kJ/mol.