The Interaction Of Hsian-Tsao Gum With Chitosan Or Gelatin And Its Effect On Food Mixed System

Using the interactions berween biopolymers,such as,oppsitely charged polysaccharides interactions,protein-anionic polysaccharide interactions,to control the microstructure,texture and rheological properties of formed complexes is a new way for developing new food systems with novel functionality.The present research on Hsian-tsao gum(HG),rich in uronic acids,mainly focused on preparation of mixed gels by the interaction with starch and herbal tea.However,the basic research on HG that was used to interact with cationic polysaccharide or protein to prepare new food systems is relatively lack.This study systematically studied the interactions of HG with chitosan(CS)or gelatin(G)as a function of HG concentration,pH and ionic strength;the complex coacervates and gels prepared by CS-HG and G-HG interactions,respectively,were characterized in detail in terms of microstructure,rheological properties,thermostability and texture.Moerover,on the basis of G-HG system,tapioca starch(S)was added to evaluate the rheological properties of G-HG-S mixed systems as a function of pH,HG and S concentration;further the mixed gels prepared by G-HG-S mixed systems were characterized in terms of microstructure,thermostability and texture.The main results were as follows:(1)The interaction mechanism of HG with CS in aqueous solution was elucidated.The zeta potential,turbidity,particle size and phase separated behavior of CS-HG mixed systems were affected by change of pH,HG and NaCl concentration.CS could interact with HG forming soluble/insoluble electrostatic complexes depending on the pH.When pH was away from pKa of CS,the CS-HG complexes were soluble.By contrast,as pH approached to pKa of CS,CS aggregates were formed,of which the surface positive charges electrostatically bonded to anionic HG molecules to form the insoluble CS-HG complexes.Additionally,added NaCl ions changing the charge density of two biopolymers further affected their electrostatic interactions,which were enhanced at lower concentrations but suppressed at higher concentrations.Optical measurements indicated the CS-HG complexes formed at pH 6.5 presented a coarsening phenomenon where the soluble electrostatic complexes aggrated to form insoluble complexes with increase of HG concentration.(2)CS-HG complex coacervates were prepared and characterized.The rheological properties of CS-HG coavervates were affected by changing pH and HG concentration.The apparent viscosity values of CS-HG coacervates were increased with HG concentration,showing shear-thinning behavior,and their storage modulus(G')and loss modulus(G")also increased.PH affecting the zeta potential of biopolymers further affected the forming type and viscoelastic modulus of complex coacervates.The CS-HG coacervates were formed molecularly through the electrostatic bonding between-NH3+ of CS and-COO-of HG,thus the crystalline structure of CS was destroyed by interacting with HG,forming a novel network within coacervates.Microstructure measurement indicated that the CS-HG electrostatic complexes forming aggregates coarsened and the surface structure changed with increase of HG concentration.(3)The interaction mechanism of HG with G in aqueous solution was investigated.The zeta potential,turbidity,particle size and distribution of CS-HG mixed systems were affected by change of pH,HG and NaCl concentration.G could interact with HG forming soluble/insoluble electrostatic complexes depending on the pH and HG concentration.Microstructure measurement indicated that pH and HG concentration within mixtures significantly affected the microstructure of formed complexes,showing that G as the center was adsorbed by HG,with tertiary structure of G changed by the interaction with HG molecules.Three critical phase transition points(pH?1,pHopt and pH?2)shifted to lower pH and pHc was kept constant with increase of HG concentration.(4)Rheological properties of G-HG mixed systems were explored.The factors of HG concentration,pH and temperature affected the rheological properties of G-HG systems.All the samples showed a shear-thinning behavior.At pH 3.5,the G-HG mixtures exhibited liquid behavior with G">G',showing no sol-gel transition,while at pH 4.5,5.5 and 7,G blended with HG could form gel network,exhibiting increased G" but decreased G' with addition of HG.The sol-gel transition time tg of G-HG mixtures varied with pH and HG concentration,leading to the mixed gel formed with different fracture stress ?f.At pH 7.0,G mixed with HG subjected to heating could form stable gel network with enhanced and fracture stress ?f,of which the apparent viscosity and viscoelastic modulus and tg were changed depending on HG concentration.(5)The properties of G-HG mixed gel were investigated.Changes in either pH or HG concentration affecting the molecular interaction between G and HG,further influenced the formation of microstructure of G-HG gels.The texture properties of mixed gel strongly associated with its microstructure.The formed gel with continuous G phase exhibited higher fracture stress than one with particulate and coarse-linear structure.As HG concentration was increased,the microstructure of mixed gel transformed from uniform to particulate,finally to coarse linear structure,this transformation resulting in the reduction in fracture stress but increase in the flexibility and deformability of mixed gel.The interaction of G with hydrophilic HG formed gel network that bounded the movement of free water,leading to the T23 shifted to lower time.(6)The ternary mixtures(G-HG-S)and mixed gels were investigated.The rheological properties of ternary mixtures and microstructure and texture properties of mixed gels were affected by pH,HG and S concentration.When HG concentration was increased within mixtures,the microstructutre of mixed gel formed transformed from particulate to fine stranded and finally to coarse stranded structure with hole.When S' concentration was increased within mixtures,the microstructutre of mixed gel formed transformed from coarse stranded to fine stranded structure.Both increase of HG and S concentration could increase the G' and G" of mixed systems,improve the fracture stress and strain of mixed gels,increase the melting temperature and thermostability,but decrease the Young modulus.The mixed gel formed through intermolecular forces(hydrogen bonds,Maillard reactions,electrostatic effects),thus affected the distribution of free water within mixed gels.