Study On The Characterization Of Fucoidan From Laminaria Japonica And Its Digestibility And Fermentability In Vitro

Laminaria japonica belongs to the genera Laminaria(order Phaeophyta).It is a macroalgae and was documented as a traditional Chinese medicine.Fucoidan is an important functional polysaccharide in Laminaria japonica and was verified to own various activities in vivo and vitro.However,its digestibility and fermentability in digestive system were rarely investigated and reported.Therefore,we investigated the digestibility and fermentability of fucoidan from Laminaria japonica and revealed the interactions between fucoidan and digestive solution as well as microbiota.Firstly,crude fucoidan(CF)was extracted from the Laminaria japonica by enzymolysis and precipitated with quaternary ammonium.The homogeneous CGF-3 was obtained after purification using chromatography.Furthermore,we studied the digestive process of fucoidan and the effects of fucoidan on the activities of various digestive enzymes by in vitro digestion model.At last,fermentation of fucoidan by human fecal microbiota and the effects of fucoidan on intestinal microflora were investigated.Details are as follows:The homogeneous CGF-3 was obtained after purification using anion-exchange chromatography DEAE-cellulose-52 and size-exclusion chromatography sepharose CL-6B,and the average molecular weight of CGF-3 was 527.3kDa.The basic composition of CF and CGF-3 was detected by chemical colorimetric method.The protein content decreased and the uronic acid content increased after purification.The monosaccharide composition was determined by high performance liquid chromatography with PAD detector,and analysis results indicated both CF and CGF-3 were mainly composed of fucose,xylose,galactose,glucose,galacturonic acid and mannose.The molar ratio of component monosaccharides of CGF-3 was 9.8:1.0:16.4:1.8:6.0:12.7,and the sulfate content was 26.74%±7.8%,indicating CGF-3 is a kind of fucoidan named as fucogalactan.DSCGF-3 was obtained and verified by infrared spectrometer for further study.The digestibility of CGF-3 in saliva,simulated gastric and small intestinal fluids and the effects of CGF-3 on digestive enzymes were investigated using an in vitro digestion model.Results showed that the molecular weight and the reducing sugar content of CGF-3 were not significantly changed,and no free monosaccharide released from CGF-3 was detected after digestion.These results indicated that the saliva,simulated gastric and small intestinal fluids showed no influence on CGF-3,the structure of CGF-3 is resistant to the saliva and gastrointestinal tract environments.The ?-amylase and pancreatic lipase inhibitory effects of CGF-3 and its desulfated derivative were evaluated.Although no significant ?-amylase inhibition was observed,CGF-3 showed the dose-dependently pancreatic lipase inhibitory activity.The inhibitory effect on pancreatic lipase of DSCGF-3 was weaker than CGF-3.This means that fucoidan may be potential to influence lipid metabolism and regular obesity in vivo.The fermentability of CF was investigated through fermentation by human fecal microbiota in vitro.CF was fermented for 48 hours.The short chain fatty acids(SCFAs)such as acetate,propionate were increased gradually,and butyrate was not detected until 48 h.The total SCFAs between CF and control(Blank)were not significantly different at 48 h.The pH of fermentation culture of CF was decreased at 6 h and maintain at a low value till 48 h.The molecular weight of CF and total carbohydrates of fermentation culture were not changed during fermentation.Although CF was not fermented,the microbiota composition was modulated by increasing the Proteobacteria population and decreasing the Bacteroidetes population.Meanwhile,it significantly increased the populations of Faecalibacalibacterium and Bifidobacterium.This study demonstrates that fucoidan extracted from Laminaria japonica can be neither digested by salivary and gastrointestinal(GI)tract nor fermented in the human large bowel.However,it can modulate the microbiota composition and inhibit the activity of pancreatic lipase.These researches indicate fucoidan can pass through digestive tract without degradation,and affect organism by modulating the activity of digestive enzymes and the composition of microbiota.This study shed a light on the mechanism of the effects of fucoidan and provided a scientific basis for fucoidan application.