The Formation Mechanism Of Konjac Glucomannan Gel Based On Topological Structure And Its Functionalization

The stability of food hydrogel in complex conditions places stricter requirements on the scientific experiments and the engineering processing.Polysaccharides have always been one of the most common raw materials for the production of hydrogel series products in the food research area.However,the molecular structure of polysaccharide hydrogels is complex and irregular,and extremely unstable during processing.It has been a challenge to control the dynamic changes of polysaccharides.Therefore,to explore green measures to form gels and dynamically controlling their molecular chains has always been one of the hot spots in food processing.This doctoral dissertation intends to use a kind of resource plant polysaccharide,KGM,as a gel model,based on the study of the topological structure of KGM,construct the concepts of "KGM molecular chain topological structure→topological structure effects on gel stability→experimental verification and evaluation".In theory,the topological network formation in the KGM gel microstructure was analyzed,and the result reveled the formation mechanism of the stability of the KGM gel.The construction of mathematics theory realize the micro-control of the KGM hydrogel,and provide a theoretical foundation and method for improving the quality food hycrogel.In practice,many other organic or inorganic food-grade raw materials was combined to produce naturally degradable hydrogels with different functions.Those hydrogels were fabricated under fine design and control with different physical and chemical methods at the molecular level,and to be applied in areas of food science and technology.We have established a complete system of hydrogel synthesis and application based on KGM,and provide more innovative ideas in the field of hydrogel fabrications from natural polysaccharide.The main co;ntents of this work include the following aspects:(1)Study on topological structure and gel stability of KGM molecular chains.In this chapter,based on the theory of network topology,we proposed several different topological structures in the formation of KGM gels,gave the theoretical guarantee of the effect of topological structure on the stability of KGM gels,and adopted three different techniques(methods)to modify KGM hydrogel in the molecular level.The topological construction bwtween KGM and other complex molecules was realized from the perspective of physics and chemistry,and a stable topology network structure which differ from KGM itself were formed.The three types of cross-linked compounds and the technical methods adopted in this chapter are:(a)Selection of silicon-based materials(sodium silicate,tetraethylorthosilicate,and nano-SiO2)as composites,to prepare the KGMbased porous food hydrogel;(b)Preparation of food microsphere ingredients based on KGM by physical and chemical degradation with polysaccharides,like sodium alginate and chitosan;(c)Selection of polymers(sodium polyacrylate polyethylene,polyacrylamide)as a crosslinking agent,to prepare a KGM-based food ingredient detector.Combined with the theory of topological network design,this chapter also proposed three different topological structures for KGM hydrogel:(a)KGM " Starlike" network structure;(b)KGM crosslinked network structure;(c)KGM double network node structure.(2)KGM hydrogel functionalization(section one):porous food hydrogel and its adsorption for metal ions.In this chapter,based on the KGM "Star-like" topological network structure,an ordered porous gel material with a honeycomb structure is obtained through organic-inorganic hybridization and vacuum freeze-drying technology.We illustrated the principles of synthesis,the structure,and the functions of a novel konjac glucomannan(KGM)-based biopolymer-silica hybrid materials.Nano-silicon dioxide(SiO2)were applied as composites,combined with KGM,to form a highly porous structure by using a simple and versatile route-freeze drying.Morphology of materials was analyzed by scanning electron microscope(SEM),while the structure was characterized by Fourier Raman spectra and Nuclear magnetic resonance(NMR)methods.Thermal stability was also detected by Thermogravimetric analysis(TGA).We systematically varied the Nano SiO2 concentration and solution pH value,and designed a new class of KGM-silica hybrid porous materials(KNSi)with honeycomb structure,tailored mechanical properties,and excellent support capacity.The results revealed that gel formation was improved by the addition of silica materials,and a relative ordered porous honeycomb structure was formed to produce a better biological polysaccharide porous silicon material under the optimum condition(2 wt%of Nano SiO2 concentration,solution pH value with 7.5).Activated carbon-loaded porous materials(CKNSi)exhibited a high Cu2+ adsorption capacity.The results showed that the copper ion-loaded gel had high copper ion adsorption performance,and the adsorption amount reached 2.87 mg/g in 10 minutes,and reached the maximum adsorption in 30 minutes.The amount was 4.38 mg/g.The resulting materials not only compare current composites with their unique thermal and mechanical properties,but are also derived from bio-based precursors through an attractive aqueous“green”process.Most importantly,these polysaccharides based porous materials have excellent microparticle loading properties.We also make best of this organic-inorganic hybrids to develop the activated carbon loaded porous materials which have a relative high Cu2+ adsorption capacity.(3)KGM hydrogel functionalization(section two):food microsphere ingredients and their protection for food components.The content of this chapter is based on the KGM cross-linked topology network structure,using konjac glucomannan as the main raw material to prepare a new type of microcapsule as a food microsphere ingredient.In this study,a novel microcapsule was generated by the encapsulation of Lactobacillus acidophilus(L.acidophilus)using konjac glucomannan(KGM)hydrogel.Micropowder of L.acidophilus was mixed with gel particles,which was encapsulated in a microcapsule wall material produced by the combination of konjac oligosaccharides(KO)and sodium alginate(SA).The encapsulation and stability(both storage and digested)along with the microstructure of the capsules were analysed by Fourier transform infrared spectroscopy(FT-IR)and scanning electron microscopy(SEM).The results revealed that the microencapsulation rate was 62.5%,Dialdehyde glucomannan(DAK)/gelatin crosslinked gel formed numerous interconnected pores,and the pore wall was thick and smooth,which could well protect the microorganisms inside.Study of the storage stability showed that microencapsulated L.acidophilus could be stored for longer at both 4℃ and 25℃.Gastric fluid simulation results confirmed that micro-encapsulation improved the acid resistance of L.acidophilus.In addition,KO was applied as both prebiotic of L.acidophilus and antifreeze agent.It is illustrated that the survival rates of L.acidophilus(with and without encapsulated)were significantly(P<0.01)increased during freeze drying situation.The use of Oligosaccharide(KO)for improvement on stability of microcapsules relies on its prebiotic activity and antifreezing property.(4)KGM hydrogel functionalization(section three):food ingredient detector and its detection for harmful components.The content of this chapter is based on the KGM double network node structure,to synthesize a microfiber by using microfluidic spinning technology.In this study,we reported a microfluidic spinning technology(MST)for fabrication of microfibers with a novel biocompatible material,konjac glucomannan(KGM)as the main material combined with sodium polyacrylate(PAAS).These as-produced KGM/PAAS microfibers are consistent and uniform in size with an average width of 100μm.The structural characterization of the fiber gel shows that the addition of sodium polyacrylate removes the acetyl group from the konjac glucomannan molecule and enhances the strength and heat resistance of the material.At the same time,the acquisition of highly viscoelastic fibers also demonstrated the formation of a double-network network of gels.Also,these microfibers can easily arrange to microarrays and microgrids,facilely forming a useful platform for molecules recognition of amines.Three kinds of amine molecular solutions were selected as the research object.It was observed by fluorescence microscopy that at 525 nm wavelength,different amine molecule-loaded array nodes have different fluorescence absorption peaks,so this array structure can serve as a micro-reaction for the identification of amine molecules.Platform.Moreover,the nontoxicity of KGM developed an ofloxacin loaded KGM microfibers present potential application in wound dressing.To conclude,this dissertation theoretically analyzed the topological network stability and rheological properties of KGM composite hydrogel,the results revealed the topological stability mechanism of KGM composite hydrogel,and provided the theoretical basis for raw material selection and process parameters for subsequent studies.Meanwhile,This study successfully prepared porous gel with ion adsorpation function,microcapsules with embedding function,and microfibers with molecular recognition function,which offers insight into a versatile pathway to the construction of biomaterial by using plant polysaccharides as precursors.