Extraction, Separation And Preliminary Structure Analysis Of Polysaccharide From Longan Fruit

Longan polysaccharide(LPS)has been proven to have several bioactivities, including anti-oxidation,anti-consenescence and anti-tumor activity,which confers Longan with high economic values.In this study,LPS was extracted,separated and purified into three constituents.The purity and the molecular weights of these three constituents were analyzed,and their basic chemical structure and characteristics were determined through various analytical techniques."Feng Li Shui" longan,one main longan breed in Tong'an,Xiamen,China,was used as the source of Longan polysaccharide in this study.Three different methods, traditional hot water extraction,microwave-assisted extraction and microwave assisted hot water extraction were applied to separate LPS from longan seed pulp.It was found that a higher yield of LPS was achieved while longan pulp was extracted by the microwave assisted hot water extraction.The result of orthogonal experiments showed that the optimal process parameters for this method were:microwave pretreatment with 700 W for 60 seconds,followed by hot water extraction with solid-liquid ratio of 1:15 under stirring speed of 240 r·min^-1at 100℃for 7 hours.The optimal yield of 9.0 mg·g^-1(dried longan biomass weight)was achieved under these parameters.The protein and small molecule impurity dissolved in the LPS extract were removed by TCA precipitation and dialysis,respectively.A DEAE 52-cellulose ion exchange column was used to further separate a neutral LPS(LPS-N)and two acid LPS(LPS-A1 and LPS-A2)from the LPS extract.The molecular weights of LPS-N, LPS-A1 and LPS-A2 were determined to be 13.8 kDa,1382 kDa and 571 kDa, respectively.Furthermore,"ultrafiltration-protein removal" and "protein removal-ultrafiltration" process were applied in ultrafiltration process to effectively separate LPS-N,LPS-A1 and LPS-A2.UV-VIS spectrum and FTIR analysis showed that three constituents of LPS, LPS-N,LPS-A1 and LPS-A2,are allβ-heterosaccharides with pyran and acetyl amino group.Analysis of the hydrolysis products of LPS-N,LPS-A1 and LPS-A2 showed that LPS-N was a heterosaccharide composed of xylose and glucose;LPS-A1 was composed rhamnose,xylose,arabinose and galactose and had 6%of uronic acid; LPS-A2 was composed of rhamnose and had 19%of uronic acid.