Abstract: 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.

Key words: Sargassum horneri; fucoidan; fucoxanthin; nanoparticles