Studies On The Rheological Behavior And Gelation Properties Of Gellan Gum

The textural properties of gellan gum were investigated by TPA;gelling temperature, gelling rate and G' were determined by usingdynamic rheological analysis; The interactions of gellan gum and CMCwith casein micelles in acidified milk drink were observed by laserconfocal microscope through covalently labeling FITC.The results of textural study show that hardness increased withincreasing gellan concentration. The hardness of 0.02%gellan increasedwith increasing calcium ions concentration until reached a criticallevel(0.015～0.02%), after which further increase in calcium resulted in areduction of hardness. At the same concentration of calcium ion, theaddition of calcium lactate caused gels to be much higher hardness thanin the addition of calcium chloride. Hardness rapidly decreased with pHfalling down; sodium citrate can decrease the hardness; and lowconcentration(0.0～12.5%) of sucrose showed less effect on the hardnessof gellan. In the mixed gels of gellan-carageenan-konjac, gellan is themost effective factor to the hardness, springiness and cohesiveness.Gelling temperature and gelling rate were studied by rheological behaviour, and both of them increased with increasing gellanconcentration, and the equation shown below:t_gel=0.43884exp(X_gellan/0.11441)+33.73519 (R²=0.989);g(t)=0.82615exp(X_gellan/0.04307)+4.60167 (R²=0.999).At the sameconcentration of calcium ion, calcium lactate exhibited greater effects onthe G', gelling temperature and gelling rate than calcium chloride. Underthe critical level of calcium ion concentration, our study indicatedexponential relationship between gelling temperature and calcium ionconcentration shown below:1/T_gel=0.00035exp(-X_i/0.00494)+0.00324(R²=0.995,calciumchloride); 1/T_gel=0.00026exp(-X_r/0.00555)+0.00324(R²=0.993, calciumlactate).In the mixed gels of gellan-carageenan-konjac, the concentrationsof gellan and calcium are the major factors which affected gellingtemperature and gelling rate. The ratio of carageenan to konjac affects thefirst stage of gelling rate which reached the highest when the ratio is 3:1.The second stage of gelling rate linear increased with increasingcarageenan concentration.Trough FITC labeling gellan gum and laser confocal microscopeobserving, our results shown that 0.005%gellan gum form continuousjuncture with 0.04%calcuim ion though there are widely void areasthroughout the gel, 0.01%gellan form homogeneous and compactnetwork. The interaction of casein micelles with gellan is different with CMC.In the acidified milk drink, few casein micelles agglomeratetogether to form a round particle, CMC coated the particle to stabilizecasein micelles with diameter 2.95-2.99μm,while gellan adsorbed ontocasein micelles with diameter 1.5-2.0μm.Gellan cannot form protectinglayer around the casein micelles particle to prevent the casein micelleparticles from agglomerating together.