Research On Gel Properties Of High-Acyl Gellan GUM/Sodium Caseinate

Gellan gum is a kind of food additives with features of low dosage, adjustable solid point, melting point and elastic strength. Gels formed by gellan gum are of high transparency, water content and flavor property. Research on gel properties of mixed gel of high acyl-gellan gum/sodium caseinate contributes to enrich the theory basis of interactions between polysaccharide and protein, moreover, theoretical direction could be offered to improve the stability during productive processes. In this thesis, the rheology behavior and gel properties of high acyl-gellan gum/sodium caseinate mixed gels are studied.The effects of shear rate, temperature, concentration, pH and concentration of calcium ion on static and dynamic rheological properties of sodium caseinate were studied by using rotational rheometer. The results showed the concentration had a pronounced effect on the flow behavior of sodium caseinate solution, and the system behaved as newton liquid when the concentration was above15%w/v. The viscosity increased with increase in concentration. Moreover, the effect of temperature on viscosity can be described by Arrhenius equation with the temperature range from30to60℃. The activation energy (Ea) was linearly related to the concentration. Viscosity of the system increased with the addition of calcium ion while Ea did not vary significantly.Concentrations of sodium caseinate and high acyl-gellan gum had remarkable effects on gelling properties, Hardness, springiness and chewiness of mixed gels increased with increasing high acyl-gellan concentration, The increase of sodium caseinate resulted in decrease of hardness and springiness. The optimum sodium caseinate concentration for chewiness was3%w/v. And cohesiveness was less sensitive to both concentrations of high acyl-gellan gum and sodium caseinate. When concentration of potassium ion increased, springiness and chewiness strengthened first then weaken, excessive potassium ion led to weaker cohesiveness, hardness was almost not affected. The addition of calcium could improve hardness, springiness and chewiness, while reduce cohesiveness. Mixed gels showed higher springiness and chewiness but hardness and cohesiveness were unchanged. The optimum compression distance was8mm, at which gels showed the best mechanical properties. Higher concentrations of high acyl-gellan gum and calcium ion contributed to higher water holding capacity, however, higher sodium caseinate concentration led to the opposite results, potassium ion showed little effects on water holding capacity.The effects of temperature, concentrations of sodium caseinate, potassium and calcium ion on static and dynamic rheological properties of high acyl-gellan gum/sodium caseinate mixed gels were studied by using rotational rheometer. Results showed that mixed gels were typical shear-thinning fluids, both increasing sodium caseinate concentration and temperature resulted in decrease of viscosity. Viscosities(η) of mixed gels increased with increasing ions(K+, Ca2+) concentrations until reached a critical level, after which further increase in concentrations led to a reduction of viscosities. It is found that dynamic storage modulus(G’) is larger than dynamic loss modulus(G") in frequency(ω) range from0.1to100rad/s under dynamic measurements, changes of complex viscosity(|η*|) were consistent with η. The creep behaviors of mixed gels could be described by Burger models, gels with larger viscosities had longer relaxation time and delay time.