Purification and bioactivity characterization of polysaccharides extracted from marine brown macroalgae (Sargassum siliquosum)

  • 王 紹華

Student thesis: Master's Thesis


Fucoidan a group of fucose-rich sulfated polysaccharides found in brown algae has been shown to possess a variety of human health-related biological activities such as immune competence regulation antitumor antioxidant antivirus and inhibition of angiogenesis Therefore fucoidan has a high potential for commercialization In light of this it is worthwhile to identify more efficient production strategies to improve the productivity of fucoidan and reduce its production cost In this study three brown algae species identified as Sargassum siliquosum Sargassum hemiphyllum and Sargassum polycystum were examined for their potential for fucoidan production First conventional hot water extraction method was applied to extract fucoidan from the algal biomass Among them S siliguosum showed the highest fucoidan production and fucose content giving a total sugar yield of 5 08% with 46 5% of fucose in total sugar To increase fucoidan yield ultrasound-assisted extraction (UAE) and microwave-assisted extraction (MAE) were evaluated The results revealed that UAE causes polysaccharide degradation and decreases fucoidan yield In contrast MAE showed high efficiency in fucoidan production which gave a total sugar yield of 6 94% dry weight under the condition of 750 W 10 minutes and a liquid/solid ratio of 15 ml/g The crude fucoidan was then purified to gain high purity With the isoelectric focusing treatment and the addition of calcium chloride to final concentration of 20 g/L most of the protein and alginate were removed Anion-exchange chromatography (AEC) was subsequently carried out for further purification Fucoidan was bound on the resin and eluted with 2 M sodium chloride in a linearly increasing gradient The fucoidan content finally increased from 33 31% to 78 26% with 70 94% of total sugar recovery This study also assayed the antioxidant anti-lipogenesis and anti-inflammatory activity of the extracted fucoidan which were investigated by DPPH scavenging effect lipid synthesis inhibition and the inhibition of pro-inflammatory cytokine (TNF)-? production respectively The results indicated that crude extract of fucoidan showed a high DPPH scavenging effect with a EC50 of 0 34 mg/mL while the inhibition of lipid synthesis and TNF-? production were not determined After purification DPPH scavenging effect decreased but anti-lipogenesis activity and anti-inflammatory activity were discovered The results show that the purified fucoidan product could inhibit 28 9% of lipid synthesis and 14 8% of TNF-? production To improve the potential biological activity of the fucoidan products partial hydrolysis was carried out to gain lower molecular weight compounds With hydrogen peroxide treatment fucoidan fractions with different average molecular weight (Mw) were obtained The results showed that antioxidant activities increased with decreasing Mw and the EC50 dropped from 2 58 to 1 82 mg/mL when the Mw decreased from 107 3 to 3 2 kDa In addition anti-lipogenesis and anti-inflammatory significantly enhanced when the Mw decreased to about 3 kDa giving a reduced level of 71 1% and 36 7% respectively Then low molecular weight fucoidan was treated with SO3-DMF method to gain high sulfate content The results indicated that when sulfate content increased from 18 7% to 32 1% EC50 of DPPH decreased from 1 82 mg/mL to 0 86 mg/mL and the anti-inflammatory activity also increased; however the anti-lipogenesis activity decreased In the last part of this study ESI-MS was used to analyze the structure of fucoidan obtained from S siliquosum The ESI-CID-MS/MS spectra indicated that fucoidan has a backbone composed of (1-3)-linked L-fucose residues and the sulfate groups are located at C-2 and C-4 of fucose residues Branches are galactose residues with (1 3)-linkages and the branching point is at C-4 of fucose residues The sulfate groups on galactose was mainly presented at C-4 and C-6 of galactose residues and some located at C-2
Date of Award2016 Sept 1
Original languageEnglish
SupervisorJo-Shu Chang (Supervisor)

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