Study On Gelation Properties Of Acid Low Acyl Gellan Gels

Now,obesity has become a global epidemic and a threat to the people's health.One way of tackling the high and rising levels of morbid obesity in today's society is to control the consumer's energy intake from foods.Therefore,there is a requirement to find ways to control the rate of food digestion without impacting on the enjoyment of the food.One approach that could impact on people's appetite and can be delivered in liquid or soft solid products without an adverse effect on consumer response,is the use of hydrocolloids that respond to the pH conditions experienced inside the stomach by self-strucutring.Gellan gum is a linear anionic heteropolysaccharide produced by Sphingomonas elodea,which has been a subject of interest since its discovery in 1980 due to its ability to form transparent gels even at low concentrations.In addition,traditional gelling agents such as agarose and carrageenan show reduced gelling capacity at low pH,whereas gellan gum can form strengthened gels.However,there are little studies on acid-induced gellan gels.In this paper,the gelation properties of acid gellan gels were investigated.The influences of hydrocolloid concentrations,GDL/LA weight ratio on the gelling properties of low acyl gellan gels formed by acidification with glucono-?-lactone(GDL)were investigated.The gelation profiles of low acyl gellan gum after addition of varying GDL proportions showed a gradual decrease in pH.Hydrocolloid concentrations and GDL/LA weight ratio had a pronounced effect on the gel strength of acid gellan gels.Fracture stress,initial Young's modulus and water holding capacity increased with the increase of GDL/LA weight ratio until GDL/LA weight ratio reached a critical level,after which further increases in GDL/LA weight ratio resulted in a reduction of failure stress and water holding capacity.The higher the hydrocolloid concentration,the larger fracture stress,initial Young's modulus and opacity index.Moreover,the fracture strain of acid gels decreased with the increase of GDL/LA weight ratio.The opacity index of the acid gels increased while fracture strain decreased as the GDL/LA weight ratio increased.Finally,these acid structures were also evaluated post-production in terms of their response to prolonged exposure to an acid environment.Exposure to the acid bath(pH=1)showed that the gel structure remains unaffected if it was originally produced when GDL/LA weight ratios were 2:1 and 4:1,but showed an increase in strength for those gels produced while GDL/LA ratios were 1:4,1:2 and 1:1.Overall the findings demonstrated that structuring as well as de-structuring of gellan acid gels can be controlled at acidic environments.The influences of gellan concentration,pH value,acidification rate on the mechanical properties,water-holding capacity,turbidity and microstructure of mixed gels formed by acidification with glucono-?-lactone(GDL)and hydrochloric acid(HC1)were evaluated.The results showed that the direct acidification tends to form a transparent gels,while the slow acidification tends to form opaque gels.The fracture stress,initial Yong's modulus and water holding capacity firstly increased and then decreased with the decrease of pH value.The optimum pH to the gel strength and water holding capacity for the acid gels was about 3.0.While,the fracture strain decreased as pH decreased.The fracture stress,initial Young's modulus and opacity index increased with the increasing of gellan concentration.Acid gellan gels have a high degree of thermal stability.The storage modulus and loss modulus of acid gels remained constant in heating.The storage modulus of acid gellan gels increased with the increase of pH value until pH value reached a critical level,after which further increases in pH value resulted in a reduction of storage modulus.The optimum pH value is 3.At the same pH,the storage modulus of gels induced by GDL is larger than gels induced by HC1.Acid gellan gels have sponge-like pore structure.The viscoelastic behavior of gellan acid solution was investigated.The results of static rheological measurements proved that the flow ability of gellan acid solution obeyed the law of pseudoplastic fluid.The viscosity increased with increase in concentration of low acyl gellan gum.The higher temperature,the smaller apparent viscosity.On the other hand,pH is almost no influence on the viscosity of acid solution.It is found through the dynamic measurements that at high temperature the acid 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.Therefore,sol-gel transition occurs on cooling in the gellan acid solutions.Magnitudes of G' and G" increased with increase of concentration.Moreover,the sol-gel transition of gellan acid solution was studied by rheology measurements.The sol-gel transition temperatures were determined from the crossover of storage modulus G' and loss modulus G".The results showed that the gelation temperature increased with the increasing of gellan concentration,while decreased with the increasing of pH.