The Content, Antioxidant Activity, and Structural Characteristics of Sodium Alginate Extracting from Sargassum polycystum Grew in Vietnam: Effect of Various Extraction Conditions

Introduction: Alginate is a biopolymer commonly in brown algae, high content, diversity in structure and bioactivity. They are applied to other fields such as food, functional food, pharmaceuticals, and heavy industry and extracted from Sargassum, Laminarin, Tubinaria and Sargassum polycystum species commonly grow in the world than another genus. The content, the antioxidant activity, and the physical chemistry properties of alginate extracting from the species did not exhibit in the previous studies. Methods: The study focused on the impact of various extraction conditions (temperature (40 to 90,degrees C), time (01 to 06, hours), the solvent-to-material ratio (10/1 to 40/1, v/w), solvent pH (8, 9, 10), and numbers of extraction (1, 2, and 3 times) on alginate content and its antioxidant activity, also evaluated sugar compositions, average molecular, viscosity, and C-13-NMR spectrum characteristics of alginate. Results: The results showed that the suitable condition for the extraction of alginate was for 4 hours at 60 degrees C with the ratio of Na2CO3 (pH 9)-to-material (40/1, v/w) and one number of extraction. The highest alginate content was 176.22 mg uronic acid equivalent/g DW, corresponding to antioxidant activity (188.54 mg ascorbic acid equivalent/g DW). Alginate possessed the intrinsic viscosity (271.86, n) and the average molecular weight (78.6, kD). Different sugar compositions of antioxidant alginate were fructose, fucose, mannose, galactose, rhamnose, mannose, and glucose. The C-13-NMR spectrum of antioxidant alginate exhibited chemical shifts of C sites of D-mannuronic (M) and L-guluronic (G), corresponded to C-1, C-2, C-6, and C-2, C-3, C-4, C-5, C-6, respectively. Conclusion: Alginate is non-toxic, therefore, antioxidant alginate extracting from brown algae Sargassum polycystum grown in Vietnam is a potential in functional food and pharmaceuticals.