In order to study the anticoagulant oligosaccharides derived from Sargassum fusiforme fucoidan (SFF), the monosaccharide composition, molecular mass and physicochemical characteristics of SFF were determined by high performance liquid chromatography (HPLC), high performance gel permeation chromatography (HPGPC) and chemical methods, respectively. Degradation of SFF was carried out using hydrochloric acid (HCl). The degradation products were separated by gel permeation chromatography on Bio-gel P4. The anticoagulant activity of the resultant oligosaccharide fractions was evaluated by activated partial thromboplastin time (APTT), thrombin time (TT), and prothrombin time (PT) assays. The oligosaccharide fraction with the highest anticoagulant activity and lower molecular mass was selected and its structural characteristics were analyzed by negative-ion electrospray mass spectrometry (ES-MS). Results indicated that SFF mainly consisted of fucose, galactose, mannose and glucose in a molar ratio of 67.11:26.69:2.54:3.66. The average molecular mass of SFF was 708 kDa and the contents of total sugar, protein and sulfate ester in it were 56.44%, 1.14% and 26.22%, respectively. Five oligosaccharide fractions, named P1 to P5, were obtained by degradation of SFF with hydrochloric acid. They all could prolong the APTT and fractions P1, P2 and P3 were more effective than P4 and P5, especially P3; however they were ineffective in prolonging TT or PT. P3, a highly pure oligosaccharide, was mainly composed of Fuc₃(SO₄)₂.

In order to prevent fucoxanthin degradation in the stomach before entering the intestine, pH-sensitive nanoparticles based on fucoidan and chitosan were constructed for the efficient delivery of fucoxanthin in the gastrointestinal environment. In this study, fucoxanthin and a fucoidan fraction were extracted from Sargassum horneri. High performance liquid chromatography (HPLC) was used to determine the purity of fucoxanthin. High performance gel permeation chromatography (HPGPC), chemical methods and HPLC were used to determine the molecular mass, physicochemical characteristics and monosaccharide composition of the fucoidan fraction. Fucoxanthin-loaded nanoparticles with different fucoidan/chitosan mass ratios of 0.6:1, 0.8:1 and 1:1 were prepared by polyelectrolyte self-assembly. Fourier transform infrared (FTIR) spectroscopy was used to evaluate the interaction between fucoidan and chitosan, and the physicochemical characteristics of fucoxanthin-loaded nanoparticles and the changes in its size, fucoidan-loading rate, and fucoxanthin-loading rate during simulated gastrointestinal digestion were determined to evaluate the stability of the nanoparticles in the gastrointestinal tract. Results indicated that the purity of fucoxanthin from S. horneri was 13.57%. The average molecular mass of the fucoidan was 342 kDa. The contents of total sugar, protein, uronic acid and sulfate group in it were 52.45%, 7.96%, 9.25% and 19.26%, respectively. Moreover, the fucoidan was composed of fucose, galactose, mannose, glucuronic acid and xylose, among which fucose and galactose were the most abundant monosaccharides. FTIR spectra showed non-covalent interactions between fucoidan and chitosan in the nanoparticles and good binding state between them. The particle size of fucoxanthin-loaded nanoparticles was 360–430 nm, the zeta potential was 26–31 mV, and the polydispersity index (PDI) was 0.23–0.27, indicating that the nanoemulsion was uniform and stable. The fucoidan-loading rate was 87%–90%, and the fucoxanthin-loading rate was 87%–91%, indicating that fucoxanthin was well encapsulated in the nanoparticles. In vitro simulated digestion experiments showed that the particle size, fucoidan-loading rate and fucoxanthin-loading rate of the nanoparticles in simulated gastric juice did not change significantly, indicating that the nanoparticles were stable in simulated gastric environment. In simulated intestinal fluid, the particle size increased significantly, and the fucoidan-loading rate as well as fucoxanthin-loading rate decreased significantly, indicating the expansion and depolymerization of the nanoparticles in simulated intestinal environment. As a result, efficient delivery of fucoxanthin in simulated gastrointestinal tract was accomplished. At the fucoidan/chitosan mass ratio of 1:1, the effect was most obvious.