Study On Sol-gel Transition And Gelling Properties Of High Acly Gellan

Gels have attracted much attention in various fields because of their possible unique applications, and investigations related to gels have been developed in recent years. Gellan gel is an extracellular microbial polysaccharide, which is an important ingredients in food industry because of their low dosage, and resistant to acid and heat. Because the gelation process affects the product’s quality directly, it is important to explore the sol-gel transition of gellan gel. In this paper, the sol-gel transition and gelation behavior of high acly gellan were studied using dynamic shear rheological analysis and texture profile analysis.Sol-gel transition of high acyl gellan gels were studied by using four different rheological methods:the crossover of storage modulus (C) and loss modulus (G"), the abrupt changes in G’and complex viscosity (η*), yield behavior of the G’,ω independence of the loss angle tanh. The results showed that the measurement of crossover of G’and G", abrupt changes in G’and η*were strongly dependent on the angular frequency (ω), and the method of yield behavior of G’could not provide the further information about critical gel. The most appropriate method to determine the sol-gel transition of high acly gellan was the method of ω independence of tanh. In addition, The sol-gel transition temperature increased with increasing gellan concentration (Cg). The relaxation critical exponent n decreased with increasing Cg but the fractal dimension df slightly increased indicating a denser structure in the critical gel with higher Cg.The influence of cations (K+, Na+, Ca2+, Mg2+) on sol-gel transition were investigated. The sol-gel transition temperature Tgel,ω and relaxation critical exponent n were determined using the method of ω independence of tanh. Tgel,ωof high acyl gellan solutions increased with increasing cation concentration, while the cation type have little influence on the sol-gel transition temperature. To achieve the same sol-gel transition temperature, the amount of monovalent ion was5-7times of the amount of divalent ion. In addition, The relaxation critical exponent (n) decreased from0.46to0.41with increasing ion concentration while the fractal dimension (df) slightly increased from2.05to2.10indicating a denser structure in the critical gel with higher ion concentration. A model was developed to describe the relationship between the ion concentration and sol-gel transition temperature of high acly gellan:1/Tgel,ω=Aln[Xi]+B. Influences of high acly/low acly gellan weight ratio(HA/LA weight ratio) and cations (K+, Na+, Ca2+, Mg2+) on the gelling properties of high acyl and low acyl mixed gellan gels were investigated by using Texture Profile Analysis (TPA). Results revealed that HA/LA weight ratio had great effect on gelling properties of mixed gellan gels. The cohesiveness and water holding capacity of the mixed gellan gels increased with increasing HA/LA ratio, while hardness decreased as the HA/LA ratio increased. Meanwhile, chewiness of the mixed gellan gels increased first and then decreased with increasing HA/LA ratio. In general, hardness and chewiness of mixed gels increased with increasing cation concentrations until cation concentration reached a critical level, after which further increases in cation resulted in a reduction of hardness and chewiness. However, the water holding capacity decreased first and then increased with increasing cation concentration. Cohesiveness and springiness were less sensitive to cation concentrations. At optimum cation concentration, mixed gellan gels with divalent cations (Ca2+,Mg2+) were stronger than that with monovalent cations (K+, Na+). There was no synergetic effect between divalent cations and monovalent cations.