Chemical composition of six edible seaweed species available in the coastal belt of Sri Lanka

Abstract

Climatic and hydrographic conditions allow several genera of seaweed species to grow along coastal belt of Sri Lanka. They are classified as green, brown and red algae depending upon the type of pigments present and other morphological and anatomical characters. Polysaccharides, extracted from seaweeds; agar, carrageenan, and alginates contains several nutritional compounds which are important substitutes used in food, agriculture and medicinal industry. Seaweeds were collected from Northwestern and Southwestern coastal belt of Sri Lanka. Samples were washed, cleaned, air dried, packed in air tight containers and kept in 4ºC in powdered form until analysis. The results show that red seaweed contains higher calcium than green and brown algae. Also brown and red seaweeds exhibited higher averages of sodium and potassium than that of green species. Significantly highest content of Na and K were recorded (P<0.001) in brown algae (Sargassum wightii) and in decreasing order in Ulva lactuca, Gracilaria eduli and Kappaphycus alvarezii. The green seaweeds showed the highest magnesium content than red and brown algae; ranging from 14.920-18.016 g/kg. Nickel (0-0.013 g/kg), manganese (0.006-0.188 g/kg) and boron (122-539 mg/kg) were recorded in high constitutes. The micro elements cobalt and chromium were not found in any of the seaweed species. The results of average proximate constitutions of different species are as follows: Carbohydrates: 56.9, 52.49, 53.5%, Protein: 11.83, 10.80, 9.25%; Ash: 2.70, 2.7, 2.78% and, Moisture: 24.67, 27.4, 23% in red, green and brown algae respectively. The nutritional evaluation shows that the mineral composition depends on the seaweed species. The mineral contents of seaweeds were significantly higher than vegetables such as soya bean white and lettuce. Therefore, these seaweed species could serve as a source of essential mineral to improve nutritional value of human diet.