Abstract: The objective of this study was to explore the main nutritional composition and polysaccharides of Sargassum wightii, and to provide a theoretical basis for exploiting and utilizing the natural resource of S.wightii. By using nutritional analysis method,the seaweed S.wightii was proved to have abundant content of mineral elements and 1.44% fat,11.78% protein,as well as 41.61% carbohydrates.The total amino acid content was 6.63 g/100 g which included 45% of essential amino acids,and the proportion of essential amino acid to non-essential amino acid was 0.81.Methionine and Cystine were determined to be the first limiting amino acid,and Lysine was the second limiting amino acid,and the essential amino index was 96 for S.wightii. Meanwhile,vitamin B-2 and beta-carotene were also detected in S.wightii, whose contents were 102 μg/100 g,11.4 μg/100 g,respectively.In addition,the crude polysaccharide was extracted from S.wightii by hot-water,followed by being refined by Sevage deproteinization method combining ethanol precipitation method and organic solvent cleaning method.The IR spectrum analysis indicated that refined polysaccharide contains uronic acid and sulphated ester groups.The above results showed that S.wightii was a kind of seaweed with high nutritional value,which may provide high protein,low fat and sulfated ester polysaccharide for health foods,and had important economic value and broad market prospect.

Key words: Sargassum wightii, chemical constituents, nutritional composition, polysaccharides, evaluation