| Sargassum thunbergii,belonging to the family of Sargassaceae,is a kind of natural edible algae,widely cultured in China,Japan,and other Asia regions.S.thunbergii has been reported to have anti-inflammatory,antioxidant,hpyerglycemic,anti-coagulation,anticancer and immunomodulatory activity and etc.Phytochemical studies have demonstrated that S.thunbergii contains various active ingredients,of which polysaccharide is one kind of main active ingredient.However,current studies on the polysaccharides from S.thunbergii and its biological activities are limited.In the present study,isolation and purification,physicochemical and structure of S.thunbergii polysaccharides were preliminarily measured.In addition,hypoglycemic and antioxidant effects in vitro were evaluated.Finally,in vitro digestion and fermentation of S.thunbergii polysaccharides and its effects on intestinal microflora were investigated.Main results are listed as follows:(1)Response surface methodology(RSM)was used to optimize the microwave extraction of S.thunbergii polysaccharides(STP-1)to obtain the maximal yield of polysaccharides.The optimal extraction conditions were extraction time 23 min,mcrowave power 547 W,temperature 80 ? and the ratio of water to material 27:1(m L/g),respectively.Under this optimal conditions,the polysaccharide yield was 2.84±0.09%,STP-1 contained 32.7% of total carbohydrate,1.86% of protein,and 15.2% of sulfates.STP-1 had two molecular weights of 190.4 kDa(80.1%)and 0.92 kDa(19.9%),and comprised of Ara,Gal,Glc,Xyl,Man,GalA,and GlcA with molar percentages of 1.94,30.7,4.54,23.2,17.6,8.11,and 13.9%,respectively.In addition,STP-1 showed strong DPPH· and ·OH radicals scavenging activities,?-glucosidase inhibitory capacity.Compared to traditional water extraction,STP-1 had stronger hyperglycemic and antioxidant ability.At the concentration of 0.05 mg/m L,the ?-glucosidase inhibition rate was 75.01%.At the concentration of 0.8 mg/m L,the hydroxyl free radical scavenging rate was 72.4%.At the concentration of 0.4 mg/m L,the DPPH free radical scavenging rate reached to 95.23%,which has acomparabe scavenging capacity with ascorbic acid.(2)S.thunbergii polysaccharides(ST-P)were extracted and fractionated using a DEAE-Sepharose fast-flow column to obtain ST-P1,ST-P2 and ST-P3.Structure analyse indicated that ST-P1,ST-P2 and ST-P3 had different chemical composition,monosaccharide composition and types of glycosidic linkages.Congo red analysis indicated that they did not have triple-helical conformation.ST-P2 and ST-P3 showed some ?-glucosidase inhibition effect.ST-P2 exhibited stronger antioxidant activities,with a lot of uronic acid and an average molecular weight of 48.8 kDa.Periodate oxidation analysis showed that ST-P2 contained(1?)or(1?6)linkages(37.80%),(1?2)or(1?4)linkages(25.70%),(1?3)linkages(36.50%).(3)In vitro digestion profiles of ST-P2 in a simulated gastrointestinal digestive system were investigated.Results showed that gastric juice couldn't change the molecular weight of polysaccharides and increase the content of reducing sugars.After digestion in simulated intestinal juice,the molecular weight of ST-P2 decreased from 47.97±0.94 kDa to 46.94±0.11 kDa,5.98±0.03 k Da,and 41.45±0.06 kDa,respectively.The content of reducing sugar content in digestive juice increased.During the whole digestion process,no free monosaccharides were generated.These results indicated that ST-P2 could be digested in the gastrointestinal digestive system and its overall structure was not damaged.(4)The in vitro fermentation of ST-P2 simulated fermentation system was further investigated.ST-P2 was mixed with human intestinal microflora.Deionized water was used as the blank control.After fermentation for 0,6,12,24,and 48 h,the pH of the glycolytic products was lower than that of the blank control.With increasing the fermentation time,the content of total sugar gradually decreased,and the content of reducing sugars increased at first but then decreased.The content of total short chain fatty acids(SCFAs)production in the ST-P2 group was higher than that of control group.After 48 h of fermentation,the proportions of Bacteroidetes and Firmicutes in the control group were 17.3% and 75.12%,respectively.In the ST-P2 treated group,the proportion of Bacteroidetes increased to 27.99%,and the proportion of Firmicutes decreased to 64%.In addition,there were an obvious increasing in the proportions of Faecalibacterium,Coprococcus and Ruminococcus,which facilitated the production of SCFAs.Therefore,ST-P2 could be metabolized in the large intestine and colon,regulating the structure of the intestinal microflora. |
PDF Full Text Request