Construction And Application Of Sodium Alginate-based Aerogels

In recent years,aerogels have attracted many interests due to good mechanical properties,high porosity,heat resistance and biodegradability.As a commonly used polysaccharide,sodium alginate is an excellent material for preparing aerogels.However,the aerogels formed by pure sodium alginate have poor mechanical properties,low porosity,and poor thermal stability,which limit their applications in food industry.In this thesis,the multi-component alginate-based aerogels were fabricated to improve the physical properties for a number of food applications.The details are as follows:(1)The aerogels based on sodium alginate and pectin were prepared by cross-linking with divalent cations(Ca²⁺)and the sol-gel method,followed by freeze-drying.It was found that with the increasing ratio of pectin,the porosity and pore size of the aerogels increased,and the water solubility and hygroscopicity were significantly enhanced.The mechanical property results suggested that the aerogels with a higher alginate ratio presented a stiffer and closer structure,while the aerogels with a higher pectin ratio were more flexible.The first-order and Korsmeyer-Peppas models suggested that these aerogels loaded with proanthocyanidins showed good controlled release.The results of the free radical scavenging activity and ferric reducing antioxidant power indicated that the proanthocyanidins encapsulated aerogels with a higher pectin content had the stronger antioxidant activity.Therefore,these aerogels have showed the great potentials in the controlled release of bioactive substances.(2)The sodium alginate/soy protein conjugates were prepared by Maillard reaction,and then freeze-dried to form aerogel templates.The results showed that the viscosity and elastic modulus of the conjugate solution were increased,indicating that the produced new macromolecules strengthened the gel network.The conjugate aerogels showed the severe aggregation and adhesion morphology,but the elastic modulus and the thermal stability were improved due to the enhanced covalent interactions.Then the oleogels were prepared,showing a good oil absorption of up to 10.89 g/g aerogel and40%oil holding capacity.Moreover,the oleogels loaded with 5%thymol had excellent antibacterial activity against Staphylococcus aureus and Escherichia coil.Therefore,these aerogels have showed the potential applications as template for preparing oleogels.(3)Sodium alginate and chitosan were mixed based on the electrostatic attractions,and cross-linked with calcium ions to obtain the composite aerogels.The results showed that the aerogels prepared with a sodium alginate/chitosan weight ratio of 3:1 and crosslinked with calcium ions had the lowest pore size.Moreover,the elastic modulus and thermal stability of the composite aerogels after cross-linking were significantly enhanced.Therefore,these aerogels have showed the potentials as food packaging materials.