Gelling and rheological properties of a polysaccharide extracted from Ocimum album L. seed.

In this study, a new polysaccharide was isolated from Ocimum album L. seed (OA), and its physicochemical and rheological properties were investigated. Ocimum album polysaccharide (OAP) was an acidic heteropolysaccharide with a molecular weight of 1935 kDa, and it was composed of five types of sugars: mannose (32.95 %), glucose (27.57 %), galactose (19.29 %), rhamnose, (15.96 %) and galacturonic acid (4.23 %). According to the results obtained from Huggins and Kraemer equations, the intrinsic viscosity was 6.9 dL/g in distilled water. The OAP solutions at a concentration between 0.1 and 1.5 %, showed shear-thinning behavior, and the Herschel-Bulkley and Cross models exhibited a high ability to describe the flow behavior of OAP solutions. The apparent viscosity of 1 % OAP solution was decreased in the presence of different concentrations of NaCl (0.1, 0.3, and 0.5 M), at different pHs (3-11), and in temperatures between 5 and 100 °C. Also, the pseudoplastic behavior was observed in all samples. In OAP solutions (0.1-1.5 %), the up and down curves in the shear stress-shear rate diagram did not coincide, which indicated time-dependent (thixotropic) behavior. Although, the thixotropic properties of 1 % OAP solution were weakened with adding NaCl (0.1-0.5 M) and at different pH (3-11). The results obtained from the dynamic oscillatory test showed that the OAP solutions at concentrations higher than 0.1 % had a gel-like behavior, and the viscoelastic moduli (G' and G″) were weakened in the presence of salt and with a change in pH. Also, in the temperature sweep test, the 1 % solution showed the behavior of thermally irreversible gels.

Polysaccharide extracted from Althaea officinalis L. root: New studies of structural, rheological and antioxidant properties.

A water-soluble acidic polysaccharide (AOP-2) from Althaea officinalis L. root was isolated by water extraction and purified by ion exchange chromatography (Cellulose DEAE-52) and gel filtration (Sephadex G-200). The structure characteristics of AOP-2 was determined by gel permeation chromatography (GPC), high performance liquid chromatography (HPLC), fourier transform infrared (FT-IR), nuclear magnetic resonance (NMR) spectrum and gas chromatography-mass spectrometry (GC_MS). The results indicated that the AOP-2 was an acidic hetropolysaccharide with the molecular weight of 639.27 kDa. The AOP-2 composed of 51% galacturonic acid, 32.56% rhamnose, 12.73% glucose and 3.71% galactose. It could be found that the main backbone chain of AOP-2 consisted of →3)-α-D-GalpA-(1→, →3)-α-D-Rhap-(1→ and→3,4)-ß-D-Galp-(1→ with branches of →4)-α-D-Rhap-(1→, →4)-α-D-Glcp-(1→ and α-D-Rhap-(1 â†’ . Thermal analysis revealed that the AOP-2 had high thermal stability and according to the results obtained from XRD analysis, it had a semi-crystalline structure. The results of Steady-shear flow and dynamical viscoelasticity showed that AOP-2 solutions exhibited shear-thinning behavior with high viscosity and a weak gel-like behavior at concentrations above 1% in linear viscoelastic region. In addition, it showed relatively high antioxidant property.