4.2. Extraction of Alginate from Brown Seaweed

Alginate was extracted from brown seaweed (Sargassum polycystum) using the cold method that was described by Chee, Wong, and Wong [57]. Approximately 20 g of air-dried seaweed powder was soaked in 300 mL of 1% CaCl₂ solution for 18 h at room temperature. Excessive CaCl₂ was then removed from the seaweed by washing it with 300 mL distilled water 3 times. The seaweed powder was then subsequently treated in 5% HCl (300 mL) for 1 h. This treated seaweed was again rinsed 3 times with 300 mL distilled water to remove HCl residues. The rinsed seaweed was then soaked in 300 mL 3% Na₂CO₃ solution for 1 h at room temperature. A total of 250 mL distilled water was added then and the mixture was left overnight in room temperature. A viscous solution of soluble sodium alginate was obtained by centrifuging the mixture at 14,000× g for 10 min at 4 °C. The soluble sodium alginate was then precipitated with an equal volume of 95% absolute ethanol. The wet sodium alginate was filtered from its solution with cheese cloth and washed with 50 mL of 95% absolute ethanol. The alginate that was obtained was finally dried in a vacuum oven at 50 °C for 24 h.