The Mechanism of Carrageenan Extraction from Eucheuma cottonii Using Alkaline Solvent

Carrageenan recovery process was developed for Eucheuma cottonii by investigating the effects of distilled water, KOH (0.1-0.5 N) and NaOH (0.1-1.0 N) as the solvent on carrageenan yield and gel properties. Extraction process was carried out with a constant ratio of seaweed weight to solvent volume (1:50; g/mL) at 80 degrees C. A certain amount of the liquid sample was withdrawn at regular interval time for analysis. Filtrate was separated from residue by pouring ethanol. The precipitated carrageenans were collected and oven dried at 50-60 degrees C to a constant weight. The extraction product was found to have virtually identical infrared spectra to the reference samples of kappa-carrageenan. Distilled water was the most efficient solvent with regard to yield but certainly not gel strength. Increasing KOH concentration led to carrageenan containing less sulfate content. In extraction process using alkali, the ion exchange occurred between cation from alkali solution and anion from sulphate in the seaweed. Compared with cation of sodium, the cation of potassium was able to form helixes aggregation indicated by the higher gel strength value. Alkali concentrations affected the gel strength of the extracted carrageenan significantly.