| Self-assemble of bio-macromolecules(proteins and polysaccharide)play a key role in the hydrogel forming,which can impact on the microstructure and functional properties of hydrogel.Because of the potential applications in food,medicine and other fields,they are worthy of further study and exploitation.Gelatin has been an important member of thermoreversible protein hydrogels on account of its strong self-assembly.The self-assemble behavior of gelatin under the intervention of microbial transglutaminase(MTG)and nano-collagen fiber was studied,the physical and chemical interactions between gelatin molecules were analysed,and the gel properties of the transport and release behavior for the active substances was evaluated.The results provided the guidance for the preparation of hydrogels,transport and sustained release of biologically active substances.Firstly,the type A gelatin and type B gelatin were taken as the matrix to crosslink by different concentrations of MTG.PAGE analysis showed that MTG could crosslink two types of gelatin molecules well.With the increase of MTG concentration,the average particle size of cross-linked products of type A gelatin increased gradually,and the surface hydrophobicity and Zeta-potential both increased firstly and then decreased.Within a certain enzyme concentration range,MTG could increase the thermal denaturation temperature of type A gelatin,which indicated that the molecular structure of type A gelatin had been changed.The microstructure study indicated that the network of type A gelatin gel became more and more compact and the shape of the hole gradually changed.The rheological evaluation indicated that the gel point of type A gelatin gel increased from 31.75? for the untreated MTG solutions to 33.22? for the treated MTG solutions with 8 U/g,and once the MTG exceeded 12 U/g,the gelatin gel system could lose the gel point and exist in a gel state.Texture measurements indicated that MTG could reduce the hardness,adhesiveness,and chewiness of type A gelatin gel.For type B gelatin,the increase of average particle size of crosslinking product was obviously lower than that of type A gelatin as the increase of MTG concentration.The surface hydrophobicity and Zeta-potential of type B gelatin showed no obvious fluctuation trend.The microstructure and texture properties of the type B gelatin gel hardly changed.The gel point of the type B gelatin gel increased from 29.54? to 32.8? with the increase of MTG concentration.In order to enhance and improve the properties of gelatin gel,nano-collagen fiber with homology of gelatin was added into the reaction system.Nano-collagen fiber could enhance the hardness,viscosity,and chewiness of type A gelatin gel,and the improvement effect of adding MTG was stronger than before.For type B gelatin gel,however,only the high concentration(? 10%)of nano-collagen fiber could have similar effects.For type A gelatin gel,nano-collagen fiber could increase the gel point temperature,and the gel point temperature reached 45.8 0C when the concentration of nano-collagen fiber was added up to 20%,and when the MTG was added,the gel point disappeared.For type B gelatin gel,the gel point temperature was changed only by adding more than 10%of nano-collagen fiber.However,the gel point temperature increased from 32.1? to 43.8? when adding amount of nano-collagen fiber was only 1%after treated with MTG.Finally,the effect of four different microgel on the in vitro release for porphyrin iron were studied.In vitro release test for 24 h showed that the MTG crosslinked the type B gelatin microgel,which has no significant effect on the sustained-release of porphyrin iron compared with the only type B gelatin microgel.After adding nano-collagen fiber,the sustained-release effect for porphyrin iron was improved in comparison to the type B gelatin microgel alone.MTG-crosslinked type B gelatin-nano-collagen fiber has the best sustained-release effect for porphyrin iron among the four mircogel. |
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