Ultrasound Effects On Molecular Chain, Structure And Antioxidant Activity Of Marine Fucoidan

Fucoidans are a class of sulfated polysaccharides from marine organisms with multi-activities. They has been reported to have various biological benefits, such as anticoagulant and antithrombotic activities, antiviral activityies, antioxidant activities, promotion of neural stem cell proliferation, protection against gastric ulcer and so on. Native fucoidan is usually with high molecular weight (Mw), which limited its utilization by human body. The Mw and structure of polysaccharides are reported to be related to their biological activities. Thus, more and more researches are focus on reducing the Mw of fucoidan to improve its diffusion into biological tissues. Generally, the low Mw polysaccharide is mainly prepared by chemical methods such as acid hydrolysis or free radical depolymerization, which would destroy its structure and damage the bioactivity. Researchers hope to find a more mild and effective way to degrade the polysaccharides.In this thesis, the ultrasonic method was applied to degrade the fucoidan from sea weeds and sea cucumber Isostichopus badionotus. The Mw, structure and antioxidant activities changes of the fucodian during ultrasonic, as well as the degradation kinetics was investigated to optimize and prediction the degradation of fucoidan. The results showed:(1) The ultrasonic process was a mild and effective way to reduce the Mw of the fucoidan. The degradation efficiency was directly proportional to ultrasonic intensity, and inversely related to temperature and sample concentration.(3) Degradation kinetics model of fucodian from Isostichopus badionotus quite was fitted to1/Mt-1/M0=kt during5-45℃.(4) According to the results of response surface methodology, the optimum temperature and ultrasonic intensity of ultrasonic degradation of fucoidan of seaweed and sea cucumber Isostichopus badionotus was7.83℃,469W/cm2and12℃,508W/cm2, respectively.(4) Structure analysis suggested that ultrasound treatment is an effective approach to decrease the Mw of fucoidan with only minor structural destruction. The fucoidan from Isostichopus badionotus have kept the tetrasaccharides-repeats as the original after ultrasonic process, with some destruction on non-sulfated fucose in the tetrasaccharide-repeat. Some sulfate groups in sea weed fucoidan might suffer minor destruction, especially those substituted at the C-4positions.(5) Antioxidant activity assay showed the antioxidant activity was slightly improved after a short period of ultrasound treatment. However, a long period of ultrasound treatment would paly a bad effect on the antioxidant activity of the degraded fucoidan.(6) Based on the results of the structure analysis and the antioxidant activity, we speculated the possible mechanism of the ultrasonic acted on the fucoidan may be a combination a mechanical and free radical degradation. The mechanical effect from shear force may paly a major role in degrading the fucoidan from Isostichopus badionotus.