Study On The Compability And Phase Behavior Of Gelatin/Hydroxypropyl Methycellulose Complex System

The interaction between proteins and polysaccharides is of importance for constructing microstructure to meet people's requirements in food taste and flavor as well as food edible film properties.Most of mixtures of polysaccharides and proteins are often accompanied by diverse phase separation and gelation behavior during processing and storage.The exploitation on the coupling of phase separation and gelation behaviors can offer opportunities for designing functional products,which is in urgent need of in-depth study.Gelatin(GA)and hydroxypropyl methyl cellulose(HPMC),as two typical protein and polysaccharide individually,were chosen to be studied as model materials.Hydroxypropyl methyl cellulose is one of the widely used polysaccharides for preparing edible film materials.HPMC films have good performance.However,HPMC is thermal-gel with low viscosity at low temperature,which lead to poor processing performance at low temperature.Gelatin is cool-gel on the other hand,and its addition can improve the viscosity and processing performance of HPMC at low temperature.The addition of HPMC in turn can improve the thermal stability of gelatin gel.The phase separation,gelation behaviors and film performance were investigated through establishing phase diagrams of GA/HPMC blend systems,combining with rheometer,UV,CLSM,mechanical tensile instrument,TGA,SEM and SAXS measurements.The effect of polymer concentration on microstructure and rheological properties of GA/HPMC blends were investigated by firstly establishing phase diagram,and then by rheometer,inverted fluorescence microscope and SAXS.The results showed that the macroscopic phase separation between GA and HPMC was strongly dependent on polymer concentrations and blending ratio.At room temperature,GA/HPMC blends formed homogeneous gels with no macroscopic phase separation when the polysaccharide proportion was less than 50% and the polymer concentration was higher than a certain value.However,GA/HPMC blends showed macroscopic phase separation systems when the polysaccharide proportion was more than 50%.With the increase of HPMC concentration from 1% to 6%,the microstructure of GA/HPMC blends gradually changed from the like-emulsion with HPMC as the dispersed phase to a bi-continuous network structure,and then a structure with gelatin as the dispersed phase,due to the incompatibility between GA and HPMC and the cool-gel property of gelatin.The gel strength of GA/HPMC blend system increased and the correlation length of the blend gels decreased with the increase of HPMC concentration.The addition of HPMC improved the thermal stability of gelatin gels.The apparent viscosity and specific viscosity of GA/HPMC blend solution with and without salt ions were studied by rheometer.The influence of blend ratio on the film microstructure,thermal stability,and mechanical properties of GA/HPMC blend films were studied by SEM,TGA and tensile instrument.The results showed that the addition of gelatin improved the shear thinning behavior of HPMC.The concentration dependence of specific viscosity for GA/HPMC blends was stronger than that of pure GA and HPMC solution,indicating the existence of phase separation.The phase separation behavior of GA/HPMC blends with KCl was more pronounced than that with Na Cl.With the increase of HPMC ratio,the heterogeneity of microstructure and thermal degradation temperature of the blend films increased.The elongation at break of GA/HPMC films decreased with the addition of HPMC.When the ratio of GA and HPMC was 5-5,the tensile modulus and tensile strength of GA/HPMC blend films had the lowest value,which was consistent with the changes in concentration dependence and critical entanglement concentration of the blends,indicating that change of continuous phase occurred at that blend point.The effect of pH on phase separation and gelation behavior between GA and HPMC were systematically studied.UV,ESEM,inverted fluorescence microscope and rheometer were used to investigate the variations of transmittance,micromorphology and gel performance of the blend systems.The results showed that GA and HPMC have good compatibility and no macroscopic phase separation was found under low pHs.When pH was higher than 4.50,obvious macroscopic phase separation occurred between GA and HPMC,and when pH was close to the isoelectric point of gelatin,the phase separation rate of the two phases became much faster.The blend gels changed from transparent to milky systems with the increase of pH.The gel strength of GA/HPMC blends and thermal stability of gelatin gel increased with the increase of pH,which is consistent with the change in microscopic morphology.Near the isoelectric point of gelatin,the electrostatic repulsion between gelatin molecules weakened,which promoted the strong self-aggregation and coarsening of gelatin molecules and increased the gelatin concentration in local areas,leading to the improvement of gel performance.The effect of gelatin bloom on the phase diagram,microstructure,rheological properties and gel performances of GA/HPMC blends was investigated by rheometer and CLSM.The compatibility and phase transition of blend systems were studied,and then coupling mechanism of phase separation and gelation on GA and HPMC was speculated.The results showed that the compatibility areas of GA/HPMC blends increased with the decrease of GA bloom.The equilibrium gel strength of GA/HPMC blends increased and the formation time of semi-gel shortened with the increase of GA bloom.The addition of HPMC increased the gel melting temperature and thermal stability of 100B-GA and decreased the gelation temperature of 100 BGA.The addition of 100B-GA in turn decreased the gelation temperature of HPMC at high temperature,which is due to the good miscibility between the two polymers.The entanglement in GA and HPMC played a synergy effect during the process of forming composite gels.GA and HPMC can form continuous phase at low temperature and high temperature,respectively,which determined the rheological property and gel performance of GA/HPMC blends.The rapid change in viscosity of the blends at about 55 ? was consistent with the aggregation of HPMC observed in the microscope.