Extraction of sodium alginate from Algerian brown seaweed: the effect of molecular weight on its physicochemical and rheological properties

Sodium alginate, a polysaccharide primarily derived from seaweed, has garnered significant attention due to its exceptional gel-forming capabilities, renewability, biocompatibility, and biodegradability, making it highly versatile for various applications. The molecular weight of sodium alginate is influenced by the type of algae used and the extraction method applied. This study presents a comprehensive investigation of sodium alginate extraction from Cystoseira brown seaweed collected on the north of Algeria’s PHARE beach in Ain Benian, Mediterranean Sea. The primary objective was to evaluate the effects of the acid-to-alkali procedure on the physical, chemical, and thermal properties of the extracted sodium alginate in comparison with commercially available sodium alginate. The findings revealed that the extracted sodium alginate exhibited a higher molecular weight than commercial sodium alginate, along with enhanced thermal stability. FT-IR spectral analysis confirmed that the fundamental structure of sodium alginate remained unchanged regardless of the extraction method. Rheological analysis demonstrated that the extracted sodium alginate behaved as a pseudoplastic fluid with shear-thinning properties and exhibited greater elasticity. Its viscosity followed the Cross model, showing a decrease with increasing temperature. These results highlight a strong correlation between the structural and thermal-rheological properties of the extracted sodium alginate. Given its improved properties, the extracted sodium alginate has potential applications in biomedical, pharmaceutical, and food industries, where enhanced gel strength and thermal stability are advantageous.