Effect of structure and relative molecular mass on viscosity: Generally, the thickener is a colloid which easily forms a network structure or has more hydrophilic groups in solution, and has a higher viscosity. Therefore, thickeners with different molecular structures may have large differences in viscosity even under the same concentration and other conditions. As the average thickening agent increases, the probability of forming a network structure increases with the increase of the average relative molecular mass. Therefore, the viscosity of the thickener is closely related to the relative molecular mass, that is, the greater the relative molecular mass, the greater the viscosity. The viscosity of foods decreases during production and storage, mainly due to the degradation of thickeners and the decrease in relative molecular mass.
The effect of concentration on viscosity: As the concentration of thickener increases, the molecular volume of thickener increases, the probability of interaction increases, and the number of adsorbed water molecules increases, so the viscosity increases.
The effect of pH on viscosity: The pH of the medium is closely related to the viscosity of the thickener and its stability. The viscosity of the thickener usually varies with the pH value. For example, when the sodium alginate is at pH 5-10, the viscosity is stable. When the pH is less than 4.5, the viscosity is obviously increased (but under this condition, the acidity is degraded due to acid-catalyzed degradation. Stable, so it is better to use under near neutral conditions). At a pH of 2 to 3, propylene glycol alginate exhibited the highest viscosity, while sodium alginate precipitated. Gelatin has the lowest viscosity at the isoelectric point, while the pH change of xanthan gum (especially in the presence of small amounts of salt) has little effect on viscosity. The hydrolysis of polysaccharide hydrazone bonds is carried out under acid-catalyzed conditions. Therefore, in foods with strong acid medium, linear sodium alginate and sodium carboxymethyl soda, which are smaller in side chains, are prone to degradation and the viscosity is lowered. Therefore, in soda, yogurt and other foods with higher acidity, it is preferred to use propylene glycol alginate and xanthan gum which have larger or more side chains and are less flammable and less prone to hydrolysis. Sodium alginate and CMC should be used in foods that are close to neutral such as soy milk.
Effect of temperature on viscosity: As the temperature increases, the molecular motion speed increases, and the viscosity of the solution generally decreases. For example, in the sodium alginate solution under normal use conditions, the viscosity decreases by 12% for every 5 to 6 °C increase in temperature. . When the temperature rises, the chemical reaction speed increases, especially under strong acid conditions, most of the colloids are greatly accelerated. When the polymer colloid is depolymerized, the decrease in viscosity is irreversible: in order to avoid irreversible decrease in viscosity, the colloidal solution should be avoided as long as possible to be heated at high temperatures. When a small amount of sodium chloride is present. The viscosity of xanthan gum varies little from -4 to +93 ° C, which is a special case of thickeners. The sterically hindered xanthan gum and propylene glycol alginate have good thermal stability.
The effect of shear force on the viscosity of the thickener solution: The viscosity of the thickener solution at a certain concentration will vary with the processing and transmission means such as stirring and pumping.
Synergistic effect of thickener: If the thickener is mixed and used, a viscosity superposition effect will be produced between the thickeners. This superposition can be synergistic. After a certain period of time, the viscosity of the system is greater than that of the mixed solution. The sum of the viscosity of each component, or the formation of a gel of higher strength. This superposition can also be attenuated, for example, gum arabic can reduce the viscosity of the gum. Sometimes, the use of a thickener alone does not give the desired results and must be combined with other emulsifiers to create synergistic effects. The thickener has a better synergistic effect: CMC and gelatin, carrageenan, guar gum and CMC, agar and locust bean gum, xanthan gum and locust bean gum.
The influence of other factors on the viscosity: In addition to the greater influence of pH and temperature on the viscosity, there are many factors affecting the viscosity. Adding a non-aqueous solvent to the sodium alginate solution or increasing the amount of a solvent (such as alcohol) that is miscible with the aqueous solution increases the viscosity of the solution and eventually causes precipitation of sodium alginate. The high concentration of surfactant will reduce the viscosity of sodium alginate, and finally the alginate will be salted out from the solution. The monovalent salt will also reduce the viscosity of the sodium alginate. Due to the different degree of polymerization, the relative molecular mass is also very different, so the thickener has no accurate relative molecular mass, and is generally expressed by the average relative molecular mass or relative molecular mass range.