Analysis of Rheological Behavior and Antioxidant Activity of Succinoglycan Exopolysaccharides with High Succinic Acid Content Obtained Through Succinic Anhydride Esterification Reaction

Highly succinylated succinoglycan (HS-SG) was obtained by reacting succinic anhydride with succinoglycan (SG) exopolysaccharide obtained from Sinorhizobium meliloti. Herein, structural analysis of HS-SG was performed through NMR, FT-IR, and GPC measurements. The rheological properties, physical properties, and antioxidant effects of HS-SG were investigated and compared with SG. HS-SG showed a tendency for the molecular weight to increase as the reaction ratio of succinic anhydride increased. HS-SG maintained the structure of SG, and the increase ratio of the succinyl functional group was confirmed through NMR and FT-IR. Rheological property analysis showed that HS-SG had a viscosity 250% higher than SG at a shear rate of 10 s^-1 when the reaction molar ratio of SG and succinic anhydride was 1:50. Furthermore, HS-SG exhibited higher thermal stability in rheological properties. The viscosity of SG decreased significantly to less than 10% above 70°C, but HS-SG maintained a viscosity value of over 20%. Additionally, DSC analysis showed that HS-SG exhibited a higher endothermic peak at 151 °C than SG at 93 °C, indicating improved thermal stability. In the DPPH, hydroxyl radical scavenging test, HS-SG had enhanced antioxidant activity. In these results, it was confirmed that HS-SG exhibits improved physical and rheological properties and antioxidant effects for the potential industrial use of biomaterials in various fields such as cosmetics, food, and biotechnology using microbial polysaccharides.