Synthesis,Properties And Microencapsulation Of Octenyl Succinic Anhydride Modified Agar Derivatives

Agar is a natural polysaccharides,which frequently used as a thickening and gelling agents in foods,biotechnology and pharmaceuticals.However,due to the defect of molecular structure and functional group types,resulting in the agar showed some disadvantages,such as high gel brittleness and syneresis,low gel transparency,which made the agar cannot meet the multiple requirements of export and partial domestic sales of agar products.Thus,to broaden agar’s applications,octenyl succinic anhydride（OSA）,a hydrophobic modify agent,was used to modified the agar’s structure and prepared the newly amphiphilic agar derivatives,the physicochemical and structural properties of modified agar（OSAR）were evaluated and then used OSAR as wall material for microencapsulation.First of all,a kind of newly agar derivative with high gel transparency was prepared using OSA as hydrophobic modify agent in aqueous solution.With the gel transparency as the index,the effect of reaction’s parameters on gel transparency was studied.When the agar/water 5%,OSA concentration 3%,pH of reaction system 8.0-8.5,reaction time 2 h,reaction temperature40°C,the degree of substitution（DS）was 0.06,and the highest gel transparency of OSAR was79.7%which increased by 32.6%compared to that of native agar（47.1%）.Then,the other physicochemical properties of the OSAR were studied.Fourier transform infrared spectroscopy（FT-IR）showed characteristic absorption of the-C=O and RCOO-enclosed to 1730 cm^-1 and1570 cm^-1 in OSAR,respectively.Scanning electron microscopy（SEM）showed the surfaces of OSAR particles became smoother and the partial surface of the particles eroded,revealing that modification mostly occurred at the surface of the agar particles.Additionally,compared to native agar（NAAR）,the gel elasticity of the OSAR increased,while the 3,6-anhydrogalactose,sulfate content,gel strength,gel dehydration rate,thermal stability,dissolution temperature,gelling temperature and melting temperature,and viscosity of OSAR all decreased.Secondly,to study the formation mechanism and the gel properties of OSAR,a series of OSAR with different DS were prepared and the structure,freeze-thaw stability and rheology of these agars were studied.FT-IR showed that the greater the DS,the more pronounced the characteristic peaks of-C=O and RCOO-exhibited in the OSAR.Nuclear Magnetic Resonance Spectroscopy（NMR）exhibited hydrophobically alkenyl chain length introduced in the OSAR and suggested that OS groups were mainly substituted at the C-2 position in agar molecules.Moreover,due to the introduction of carboxyl groups and branching chains,the syneresis of agar derivatives showed that the freeze-thaw stability of OSAR improved,and the more significant improvement of freeze-thaw stability with the greater DS.The value of pH and salt ions have significant effects on the freeze-thaw stability of agar gels and freeze-thaw stability of agar gels under neutral conditions is better than that of gels under acidic or alkaline conditions,and the exists of salt decreased its freeze-thaw stability.The rheology findings revealed agar was thermo-reversible gel.Compared to the native agar,the transition temperature of the agar changed,whilst viscoelasticity of the OSAR significantly decreased,indicating that OSAR showed a more liquid-like property.Moreover,differential scanning calorimetry（DSC）showed the required temperature for OSAR from gel to melt reduced and OSAR showed a more regular network structure,which attributed to the changed structure.Finally,due to the good emulsifying properties of agar and the decreased gelling point of OSAR after hydrophobically modification,the OSAR could be used as wall materials and carriers of lipophilic components.Thus,to improve the emulsifying capacity of single alginate,OSAR and alginate were used as composite materials to prepared microcapsules containing soybean oil using complex coacervation method.The highest oil yield of complex bead was obtained at:the concentrate of alginate 1%,the ratio of alginate and agar derivatives 1:1,oil concentration 4%and CaCl₂ concentration 3%at 45°C.Compared to the emulsions without the addition of OSAR,the emulsification stability of mixed emulsions improved.The particle size of microspheres was 1200μm,the oil loading content reached 40.5%,the encapsulation yield and efficiency were 62.75%and 97.59%,respectively.Moreover,the oxidative stability of soybean oils improved after encapsulation compared to the soybean oil unencapsulated or the beads without the addition of OSAR.These results showed the mixed beads had a good encapsulation effect,which could be used as wall materials for the encapsulation and delivery of lipophilic materials.