Preparation Of Sargassum Pallidum Polysaccharide Nanoparticles And Its Application In Edible Films

Sargassum pallidum,as a typical brown alga,contains lots of bioactive substances,which has high value for edible and medicinal purposes.Current researches indicated that S.pallidum is rich in active polysaccharides,which show remarkable physiological activities and functional properties like antioxidant,antidiabetics,antithrombosis and thickening.In this study,the polysaccharides were separated from S.pallidum by hot water extraction and fractional ethanol precipitation.Their physicochemical properties,antioxidant and antibacterial activities were comparatively investigated.The nanoparticles of S.pallidum polysaccharides were prepared by anti-solvent precipitation method.Edible films made of S.pallidum polysaccharide(or its nanoparticles)and chitosan were used to compare the effects of different component compositions and component ratios on their mechanical properties,practical properties and application properties.This study provided a technical basis for the development and utilization of S.pallidum polysaccharide and polysaccharide-based edible films.The main research results are as follows:(1)Three polysaccharide fractions,named as SPP-30,SPP-60 and SPP-90,were obtained by hot water extraction and fractional ethanol precipitation(30%,60%and 90%,v/v).Physicochemical characterization showed that three polysaccharide fractions had different contents of neutral sugar,protein,uronic acid,and sulfate group.Monosaccharide composition analysis showed that SPP-30,SPP-60 and SPP-90 were mainly composed of fucose,arabinose,galactose,glucose,xylose,mannose and glucuronic acid but in different molar ratios.High performance gel permeation chromatography(HPGPC)analysis indicated that the molecular weight distributions of SPP-30,SPP-60 and SPP-90 ranged from 3.77 to206.73 k Da,5.55 to 189.44 k Da and 4.92 k Da,respectively.Scanning electron microscopy(SEM)analysis showed that they had different surface morphology and sizes of fragmentation.Specifically,the polysaccharide with lower molecular weight showed more irregular fragments.In vitro bioactivity assays indicated that the three polysaccharides exhibited significant DPPH·,ABTS~+·,·OH and oxygen free radical scavenging activities,among which the fractions with higher contents of glucose and uronic acid(SPP-30)and lower molecular weight(SPP-90)performed better.Besides,SPP-60 with higher sulfate content showed better inhibitory effect on Staphylococcus aureus compared with SPP-30,while SPP-90 inhibited the growth of both Staphylococcus aureus and Escherichia coli.(2)The S.pallidum polysaccharide nanoparticles(n SPP)were prepared by antisolvent precipitation method.The optimization of preparation process,structural characteristics and functional activities of n SPP were studied.Results indicated that the average size,Zeta-potential and polydispersity index of n SPP-30 were 229.63±7.63 nm,-28.43±0.50 m V and 0.41±0.02,respectively.FT-IR and SEM analysis showed that n SPP-30 exhibited spherical or rod-like structures,which referred to the breaking of S=O bond and the formation of lactones.X-ray diffraction(XRD)and thermogravimetric(TG)analysis indicated that SPP-30 had ordered crystal structure and favourable thermal stability,which was similar to n SPP-30.In vitro antioxidant experiments showed that nanocrystallization was effective to enhance the biological activity of SPP-30.Thymol interception and dynamic release tests showed that n SPP-30 had a higher interception rate of thymol than SPP-30(86.27±0.10%vs81.96±0.04%),leading to the function of sustained release.(3)The chitosan-based edible films with different contents of SPP-30(CH,0.2SPP/CH,0.4SPP/CH,0.6SPP/CH,0.8SPP/CH),nano-polysaccharide edible film(0.4n SPP/CH)and polysaccharide-based antibacterial films(TH/SPP/CH and TH/n SPP/CH)were prepared by blade casting process.Rheological tests showed that the addition of SPP-30 or TH as well as the substitution of n SPP-30 for SPP-30 could increase the viscosity of the film-forming solution.With the increase of SPP-30 content and the addition of TH,the thickness of edible films increased but their mechanical strength decreased at the same time.However,this phenomenon could be alleviated after replacing SPP-30 with n SPP-30.FT-IR and XRD analysis revealed good compatibility among the film components.With the increase of SPP-30 content,the surface roughness of the films also increased gradually.The directional movement of TH resulted in the microscopic phase separation of TH/SPP/CH.Nonetheless,this phenomenon could be improved with the addition of n SPP-30,showing a smooth surface morphology than it had been.In addition,the oxygen and moisture resistance of SPP/CH films increased firstly and then decreased as the increasing of SPP-30 content,among which the 0.4SPP/CH performed best.Interestingly,these properties could be further improved in0.4n SPP/CH,with the lowest water vapor transmittance of 0.082±0.00 g·mm/(m~2·h·k Pa).The addition of thymol improved the hydrophobic properties of the films,reduced their water content and water absorption,and increased water contact angle as well.(4)Edible films exerted fruit refreshing effect through preventing water from evaporating,adjusting gas atmosphere and isolating external pollution.0.4n SPP/CH and0.4SPP/CH showed better application potential due to their compact structures and barrier abilities,while TH/n SPP/CH showed stronger microbial inhibition activity after adding antibacterial factor.