Effect Of High Intensity Ultrasound On Rheological Behavior And Gelation Properties Of Low Acyl Gellan Gum

Food product developers are constantly looking for new functional ingredients to improve or modify food textural attributes in order to meet consumers'demands.One of the ways to achieve this is to modify the functionality of existing ingredients.Application of high intensity ultrasound?HIUS?in food industry is currently attracting much attention because it can be used to alter food physical or chemical properties with a low impact on the environment.This work investigated the impact of high intensity ultrasound?HIU?pretreatment on the gelation properties and rheological behavior of low acyl gellan?LA?.The effects of gellan concentration,temperature,ultrasonic time and ultrasonic power on the rheological behavior of gellan solution were investigated.The results of steady rheological tests showed that temperature and gellan concentration have a remarkable effect on the rheological behavior of gellan solution.The flow curves of gellan solution can be divided into two regions,the Newton flow region at low shear rate and shear thinning region at high shear rate when the temperature is not exceeding 25 ?.The apparent viscosity of the gellan solution increased with increasing the gellan concentration.The apparent viscosity of gellan solution decreased with the increasing of ultrasonic power.While,ultrasonic time has little effect on the rheological behavior of the gellan solution.It is found through the dynamic measurements that storage modulus?G??and losss modulus?G??decreased with the increasing of temperature.At high temperature the gellan solution showed viscoelastic behavior typical of a dilute polymer solution with G?<G".While at low temperature,G?becomes higher than G"and a plateau appears indicating the three-dimension network formation.The higher gellan concentration,the higher G?and G?.Ultrasound has a little influence on the G?and G?,while the G?and G?decreased with the increasing of ultrasonic power.Moreover,diffusing-wave spectroscopy?DWS?was used to investigate the micro-rheological properties of gellan gelation.It was found that ultrasonication could delay the gel formation,but the addition of GDL will accelerate the Brownian motion of the particles in the system.The influences of gellan concentration,GDL/LA weight ratio,ultrasonic time and ultrasonic power on the mechanical properties,water-holding capacity,turbidity and microstructure of acid gellan gels formed by acidification with glucono-?-lactone?GDL?were evaluated.With the increasing of gellan concentration,the opacity index,fracture stress,initial Young's modulus and water holding capacity increased,but fracture strain decreased.The fracture stress and initial Young's modulus firstly increased and then decreased with the decrease of GDL/LA weight ratio.The optimum GDL/LA weight ratio to the gel strength for the acid gels was about 1:1.One the other hand,the water holding capacity and fracture strain decreased with the increase of GDL/LA weight ratio.With the increase of ultrasonic time and ultrasonic power,the fracture stress,initial Young's modulus and water holding capacity slightly decrease.The higher the gellan concentration,the more dense microstructures.In addition,the effect of ion species and intensity on the properties of gellan gum after ultrasonication was also investigated.The results showed that ion has a significantly influence on the gelation properties of gellam solution.With the increasing of ion concentration,the opacity index and water holding capacity decreased,while the fracture strain increased.The fracture stress and initial Young's modulus increased with the increase of ion concentration until ion concentration reached a critical level,after which further increases in ion concentration resulted in a reduction of failure stress and initial Young's modulus.Gels with Ca²⁺and Mg²⁺were stronger and firmer than gels with Na⁺and K⁺.Moreover,there exists a critical value?300 W?,when ultrasonic power is over it,the ultrasound has no effect on the gelation properties of ion-induced gellan gels.