Self-assembly Behavior Of Lysozyme/Polysaccharide System And Its Ragulation

Proteins and polysaccharides, two kind of essential biopolymers in food, their phase transition in micro or macro-structural perspective and the nano or micro- self-assembly based on the non-covalent bond, especially induced by the conditions of food processing, could be favor to design the micro-structure of food products, enrich the food styles and produce novel food structure. On the other hand, the nano or micro- self-assemblies prepared with biopolymers would provide more choices for the vehicles in the food and medical field. In this paper we research the phase transition of κ-carrageenan(CRG), xanthan gum(XG) and lysozyme(Ly) based on the non-covalent interaction from the micro or macro perspective, as well as the self assembled behavior. The potential application in solubilizing and protecting of curcumin(Cur) is studied. The successive phase transited model of XG/Ly mixture is established. The effects of polysaccharide on the structural and enzyme activity of Ly in natural and thermally treated conditions, and on the assist or green fabrication of inorganic materials from the point of the relation between the material structures and the conformation of polysaccharide are both discussed. In this paper, the main research results are as follows:1. The phase transition of XG/Ly system is pH-dependent. The system transited from co-solubility state to soluble complexes, and finally tenuous network as the pH further decreased. The network was cross-linked of XG chains by Ly resulting in the sol-gel transition by electrostatic interactions. XG could improve the thermal stability of Ly, but it could not prevent the fate of degeneration, aggregation and gelation. The heat-induced phase behavior is different in different pH, including co-solubility, micro/nano structural state and associative phase separation. A regular spherical morphology, size-controlled(61.7nm-108nm) XG/Ly NPs were fabricated in alkali coupled thermal condition. The NPs exhibited favorable distribution and stability within one month. XPS shown both XG and Ly interpenetrated on the surface of the formed NPs. Induced by the alkali and thermal treatment, XG and Ly lost their initial structures and explored more hydrophobic areas. Meanwhile, a trend transition from α-helix to β-sheet was demonstrated for Ly. Molecular rearrangement and gelatinizing were induced by the hydrophobic interaction. Subsequently, the metastable XG/Ly complex coacervations assembled by hydrophobic interaction turned to be a stable nanoparticle driven and stabilized by hydrogen bonding during the anneal process.2. XG/Ly NPs are not stable when pH decreased, but exhibit excellent stability when suffer vortex and homogenization. The XG/Ly NPs are used as particulate emulsifier for the preparation of Pickering emulsions and found the energy input decreased the pH sensitivity of the emulsions. The hypothesis is proposed XG/Ly NPs may interact with hydrophobic areas in the oil resulting in a more solid interface layer and improve the stability of emulsions.The crystal violet adsorption capacity could reach to 90% and 105% for vortex and homogenized prepared emulsions in the concentration range of 2.5-20 mg/L.3. Tunable Ly/XG nanogels were fabricated through regulating the pH of Ly/XG mixtures which has been exposed moderate alkali-coupled thermal treatment. The switched behavior could be transferred between cosolubilization and nanogels when the pH of solutions changed between 7 and 11. The pH-response of the samples exhibited favorable repeatability. The phase transition showed “S” style, and co-solution, nanogels and superstructures could obtain at stage Ⅰ(pH>9.0)、Ⅱ(pH 6.0-9.0)、Ⅲ(pH<9.0) based on the Ly/XG NPs could be obtained at different pH stages as it was tunable adjusted. The superstructures are aggregated with the unit of Ly/XG nanogels at stage Ⅲ. The initial pH affects the sensitivity and phase stage of XG/Ly system, but it does not change the phase transition.4. CRG and Ly spontaneously formed CRG/Lys complex via physical interactions. During the complexation, CRG could change the senior structure and improve the thermal stability of Ly. The hydrophobic domain of CRG/Ly complex could load the hydrophobic active substances. The solubility of Cur could improve 600 times in CRY2 system. At the same time, the stability and bioactivity in pasteurization and ultraviolet radiation are also improved. At different pH, protein/polysaccharide ratio and salt concentration, improve protein concentration would promote the of CRG/Ly complex to self-aggregate into structure with a large size due to the gradual association of complex to form lager interpolymeric complexes. The tunable process could control the dissociation and association behavior between interpolymeric complexes and soluble complex by pH. All systems shared high NaCl(0-25 mM) tolerance behavior. Heat-induced self-aggregation exhibited a temperature and polymers ratios dependant manner.5. In non-thermal condition, the effects of polysaccharides on the structure of Ly is depend on that the interaction between them. CRG has strong attractive interaction with Ly and further form soluble complex. Therefore, the complexation could change the structure, spectral properties of Ly, and further decrease it enzymatic activity. After complexation with CRG, the activity is reduced to 1/4 of initial value. But high and small molecular weight neutral polysaccharides, konjac glucomannan(KGM) and inulin, have not obvious influence on the structure of Ly. The effect of the three kind of polysaccharides on the thermal behavior of Ly is different. CRG and KGM could improve the thermal stability and could not produce phase separation even the temperature high than the thermal denaturation of Ly. However, inulin do not produce any effect for the small molecular. Heating could promote the rate for changing the structure of Ly form the Uv-vis absorption spectra and fluorescence spectra. The capacity of changing structure of Ly is in following order: CRG>KGM>Inulin.