Effects Of Drying Methods And Molecular Modifications On The Physicochemical Properties And Biological Activities Of Polysaccharides From Sargassum Pallidum

Sargassum pallidum?Turn.?C.Agardh,commonly known as“big leaf seaweed”,is a typical brown alga widely distributed in China,South Korea and other Asian countries.It is widely consumed by people as a medicinal and edible resource in China.According to the record of“Chinese Pharmacopoeia”,it has benefical functions of eliminating phlegm,softening,dispersing,benefiting water and reducing swelling.Phytochemical studies have indicated that S.pallidum is rich in active polysaccharides with various beneficial physiological activities,including anti-oxidation,anti-proliferation,hypoglycemic,and auxiliary activities.Previous studies have shown that processing methods and structural modifications have a significant impact on the physicochemical properties and biological activities of polysaccharides.However,the effects of different drying methods and chemical modification on the polysaccharides from S.pallidum are still unclear.Therefore,this paper investigated the effects of three different drying methods?freeze drying,vacuum drying and hot air drying?,sulfation modification,and selenization modification on the physicochemical properties,chemical structure and biological activities of polysaccharides from S.pallidum.The results will lay a theoretical foundation and technical support for the processing and utilization of polysaccharides from S.pallidum.The main results were listed as follows:?1?Three polysaccharides,designated as FD-SPP,VD-SPP and HD-SPP,were prepared from S.pallidum by hot air drying,vacuum drying,and vacuum freeze drying methods,respectively.The chemical composition,structure and antioxidant activity of the three polysaccharides were comparatively investigated.The results showed that FD-SPP,VD-SPP and HD-SPP had different contents of total sugar,protein,monosaccharide composition,and molecular weight.Ultraviolet spectroscopy,Fourier transform infrared?FT-IR?spectroscopy,scanning electron microscopy?SEM?,and X-ray diffractometry analyses indicated that the three polysaccharides had different structural characteristics and crystallinity.The results of in vitro antioxidant experiments indicated that FD-SPP had the strongest DPPH free radical scavenging ability,ABTS free radical scavenging ability,and iron ion chelation ability.These results indicated that the drying methods had a significant effect on the chemical structure and biological activity of the polysaccharide from S.pallidum.The freeze-drying method is a rational choice for the preparation of polysaccharides from S.pallidum.?2?The three sulfated derivatives,designated as S-SPP_1–4,S-SPP_1–6–6 and S-SPP_1–8,were prepared from polysaccharides from S.pallidum by chlorosulfonic acid-pyridine method.Their chemical composition,in vitro antioxidant,and hypoglycemic activity were studied.Physicochemical characterization indicated that sulfated modification had successfully occurred.The degrees of substitution?DS?of S-SPP_1–4,S-SPP_1–6 and S-SPP_1–8–8 were 0.85,0.91and 1.19,respectively.Structural analysis showed that the sulfation modification had some effects on the chemical composition,molecular weight,and monosaccharide composition of the polysaccharides.S-SPP_1–4 exhibited the best DPPH and ABTS free radical scavenging activities,while S-SPP_1–8 exhibited the best?-glucosidase inhibitory activity and promoting-effect on glucose consumption in insulin resistant?IR?-HepG2 cells.Furthermore,all the sulfated derivatives exhibited better hypoglycemic ability than native SPP.These results suggested that appropriately sulfated modification could enhance the antioxidant and hypoglycemic activities of S.pallidum polysaccharides,which might be used as an alternative derivative of natural antioxidant and hypoglycemic agent.?3?The polysaccharides?SPP?from S.pallidum was selenized by the sodium selenite/diluted nitric acid method.The effects of selenization on the physicochemical and biological properties of SPP were studied.The results showed that the selenium content of Se-SPP was increased from 8.15 to 2419?g/g.High performance gel permeation chromatography?HPGPC?and SEM analyses showed that selenization modification had certain effects on the molecular weight and surface morphology of SPP.FT-IR spectroscopy showed that a new absorption peak appeared at 675 cm^-1 in Se-SPP,indicating that the group on the SPP structure was replaced by selenium.Bioactivity assay showed that Se-SPP had higher free radical scavenging activity and ferrous ion chelation ability than SPP.In addition,Se-SPP showed stronger?-glucosidase compared with SPP and acarbose.Its inhibition type was non-competitive inhibition,and the half-inhibitory concentration(IC₅₀)values of SPP,Se-SPP and acarbose were 1.579,0.896,and 2.742 mg/mL,respectively.?4?The cellular antioxidant activity of selenized polysaccharides was studied using ABAP-induced HepG2 cell injury model.Superoxide dismutase?SOD?,catalase?CAT?,and malondialdehyde?MDA?were used as three antioxidant damage markers.The results showed that both SPP and Se-SPP could significantly increase the activities of SOD and CAT,and significantly reduce the content of MDA produced by intracellular lipid peroxidation in a dose-dependent manner.These results suggested that Se-SPP can be used to develop a new selenium-complementary ingredient in functional foods.