Effect of Extraction Methods on the Yield and Physiochemical Properties of Polysaccharides Extracted from Seaweed Available in Sri Lanka

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Agar, carrageenan and alginate are high valued seaweed polysaccharides, which are used as gelation and thickening agents in different food, pharmaceutical and biotechnological industries. The annual global production of the polysaccharides has recently reached 100,000 tons with a gross market value just above US$ 1.1 billion. In Sri Lanka although several seaweed species are available, there is no systematic study on comparison of method of extraction, yield and physicochemical properties of polysaccharides from seaweeds. Seaweed species Gracilaria edulis, Gracilaria verrucosa, Kapphaphycus alverazi and Sargussum wightti were collected from North and South coast of Sri Lanka. Gracilaria edulis and Gracilaria verrucosa were used for agar extraction with acid and alkaline treatments. Carrageenan was extracted from Kapphaphycus alvarezii using alkaline treatments. Three types of carrageenan (kappa, iota, lambda) were separated using freeze thawing, jelly pressing and alcohol precipitation methods respectively. For the extraction of alginates from Sargussum wightti samples were treated with acid and alkaline and hot and cold extraction methods were used. Some of the above physiochemical properties were compared with commercial available products. In agar yield (16.6%) of acid treated Gracilaria eduliswas high when compared to Gracilaria verrucosa. The gel strength was high in alkaline treatments (429 g.cm2) and was obtained from G. verrucosa. Freeze thawed method gave the highest yield (23.4%) and gel strength 715 g/cm2 in kappa carrageenan extracts. The highest alginate yield (35%) was obtained from Sargussum wightti in hot extraction treatments. The mean viscosity of agar and carrageenan purchased from commercially and extracted polysaccharides didn’t show significant difference. When considered the proximate composition mean crude protein contents of extracted and commercial products were not significantly difference on dry weight basis among agar, carrageenan and alginates. The mean value of iodine content of extracted and commercial product obtain from agar carrageenan and alginates were range from 32-58; 26-45 and 43-57 mg/l respectively. The mean sodium content of agar, carrageenan and alginates were significant difference between extracted polysaccharides and commercial product. There is also significant difference in the calcium contents of agar, carrageenan and alginates respectively. Chemical properties of agar carrageenan and alginates extracted in laboratory were more superior when compared to those properties of the products collected from the local market, but physical properties were at comparable levels. Considering the above extracted product can be promoted for commercial market.