Physicochemical, Thermal and Rheological Characteristics of a Novel Mucilage from Chia Seed (Salvia Hispanica)

Chia seed gum (CSG), an anionic heteropolysaccharide, was isolated from the seed coat of chia seeds (Salvia hispanica L.). The physicochemical, thermal and rheological properties of the purified CSG were studied. CSG was found to be composed of a tetrasaccharide repeating unit consisting of β-D-xylose, α-D-glucose and 4-O-mehtyl-α-D-glucuronic acid. FTIR and zetapotential analyses revealed the presence of a large proportion of carboxylic acid groups in CSG indicating polyelectrolyte functionality. CSG samples produced weak gel-like mechanical spectra, with G’>G” and a weak frequency-dependence in both moduli. The complex dynamic viscosity (|η*|) values of CSG solutions were higher than the corresponding steady-shear viscosity (η), i.e. η(γ)<η*(ω) values. CSG solutions exhibited Newtonian behaviour at low shear rate and pronounced shear-thinning behaviour at higher shear rate. The transition from dilute to semi-dilute regime was found to occur at the critical concentration (C*) of 0.3 g dL⁻¹. The intrinsic viscosity was ∼16 dLg⁻¹ and zero shear viscosity was found to correlate with the gum concentration as η₀ ∝ c^1.5 in the dilute regime (<0.3 g dL⁻¹) and η₀ ∝ c^2.7 in the semi-dilute regime (>0.3 g dL⁻¹ ). Acid hydrolysis yielded various molecular weight fractions with fairly uniform polydispersity giving the Mark-Houwink-Sakurada relationship of [η]=1.52×10⁻⁴ M^0.803 dL g⁻¹. Differential scanning calorimetric and thermogravimetric analyses showed that CSG was resistant to thermal degradation below 244°C. Due to the high intrinsic viscosity and low critical concentration, CSG can be considered as a promising stabilizer in many food formulations.