| Costaria costata is an annual brown alga, which mainly distributes in certain sea areas, such as the north coast of the Pacific Ocean, Hokkaido of Japan, and Peter the Great Bay. C. costata has been used as edible seaweed for a long time in Japan. In recent years, C. costata has been successfully cultivated in China, but its utilization has not yet been establised. This study has determined the nutritional composition of C. costata, the structure and properties of its alginate, the chemical composition and primary structure of its fucoidan. This study has established the theoretical basis for comprehensive development and utilization of C. costata.The nutrition composition of C. costata harvested in May, June and July was determined. It indicated that the content of moisture, ash, protein, lipid, crude fiber and phenolic compounds was increasing with growth and the highest content of them was 10.50%,29.25%,18.15%,2.21%,5.68% and 4.796 mg/g respectively. The content of essential amino acids was 32.61% and 32.91% in May and June. The content of unsaturated fatty acids, which mainly consist of palmitoleic acid and linoleic acid, was 86.43% in May, and 83.78% in June. But saturated fatty acids were abundant in July and the content of them was 48.03%. Mineral elements analysis showed that the content of calcium and magnesium was high. The content of alginate was 22.90%,29.13%, and 22.49% in May, June and, July successively.Crude fucoidan was isolated from C.costata by four methds:water extraction, acid solution extraction, enzyme extraction, and ultrasonic and SDS assisted extraction. Comparing different extraction methods of fucoidan showed that enzymatic method was the best method for the highest yield and high SO42- content. The yield of crude fucoidan was 2.58%,8.094%, and 4.183% in May, June, and July respectively. The total sugars content was 20.350%,27.712%, and 30.280%, the fucoidan content was 25.204%,29.958%, and 14.348%, and the SO42- content was 4.962%,13.097%, and 11.168% in May, June, and July.The molecule weight, viscosity, gel strength, M/G and rheological characteristics of alginate have been studied. The results indicated that the molecule weight was 3.981×106 Da,3.731×106 Da, and 1.410×106 Da, the viscosity was 1026.7 mPa-s, 419.7 mPa·s, and 104.8 mPa·s, the gel strength was 1,449.0 g/cm,1,935.0 g/cm, and 980.5 g/cm, and the M/G ration was 2.030,1.415.1.306 in three months. The viscosity of the alginate sodium solution increased as its concentration increased, and decreased as the temperature rised. So alginate solution was proved to be the pseudoplastic fluid with shear thinned. The thixotropy of alginate of different months was similar. Alginate solution had viscoelastic properties. Viscidity was the main property of the alginate solution in the low frequency area while the elasticity was dominant in the high frequency area, and the point of intersection of G’ and G" decreased from May to July.Fucoidan extracted from C. costata in June and July was noted as 6F and 7F. Then 6F and 7F were purified through Q-Sepharose FF anion-exchange chromatography to obtain fucoidan fractions 6F0,6F1,6F2, and 7F1. Monosaccharide composition determined by gas chromatography indicated that the monosaccharide composition of each fraction was heterogeneous. Fraction 6F0 had the highest fucose content as 62.362%, and other major monosaccharide were fucose, mannose and galactose. The molecule weight of 6F0,6F1,6F2, and 7F1 was 15.668-4.966 kDa, 433.511 kDa, and 4.721 kDa. Molecule structure of fractions was detected by infrared spectroscopy,1H-NMR and 13C-NMR. The infrared spectroscopy spectrogram of 6F1, 6F2, and 7F1 had the similar absorption bands of sulfuric acid, uronic acid and sugar ring characteristic groups.’H-NMR spectrum revealed that 5.68 ppm,5.14 ppm,5.04 ppm,4.94 ppm,4.84 ppm,4.65 ppm, and 4.57 ppm were the signal peaks of fucose, xylose and rhamnose, galactose, arabinose, mannose, and glucose respectively. It also indicated that 3.69 ppm,2.12 ppm, and 1.36 and 1.2 ppm were the signal peaks of oxygen methyl, acetyl and fucose methyl protons.’C-NMR spectrum showed that 100.06 ppm,99.92 ppm and 99.87 ppm were a-L-fucose anomeric carbon signal peaks, and that 74-88 ppm was sulfate groups,61 ppm was C6 of β-galactose, and 15.75 ppm was methyl fucopyranose. |
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