Factors affecting the effectiveness of food thickeners

Influence of structure and relative molecular mass on viscosity: Generally, thickeners are colloids that can easily form a network structure or have more hydrophilic groups in solution and have a higher viscosity. Therefore, with different molecular structure of the thickener, even in the same concentration and other conditions, viscosity may also have a large difference. The same thickener species, with the increase in the average relative molecular mass, the chance of forming a network structure also increases, so 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 main reason for the decrease in viscosity during the production and storage of food is the degradation of the thickener and the decrease in relative molecular mass.

The influence of concentration on viscosity: as the concentration of thickener increases, the volume of thickener bullet increases, the chance of interaction increases, the adsorbed water molecules increase, so the viscosity increases.

PH value on the impact of viscosity: the pH value of the medium and the viscosity of the thickener and its stability of the relationship is very close. The viscosity of the thickener usually changes with the pH, such as sodium alginate at pH 5 to 10, the viscosity is stable; pH less than 4.5, viscosity increased significantly (but in this condition due to acid-catalyzed degradation, resulting in unstable viscosity, so it is better to use in close to neutral conditions). At pH 2 to 3, propylene glycol alginate shows the greatest viscosity, while sodium alginate precipitates and precipitates. Gelatine has the lowest viscosity at the isoelectric point, while xanthan gum (especially in the presence of small amounts of salt) has little effect on viscosity due to changes in pH. The hydrolysis of polysaccharide glycoside bonds takes place under acid-catalyzed conditions, so in foods with strong acid media, straight-chain sodium alginate and smaller side-chain sodium carboxymethylcellulose are prone to degradation resulting in a decrease in viscosity. Therefore, in foods with high acidity such as soft drinks and yoghurt, it is advisable to use propylene glycol alginate and xanthan gum which have larger or more side chains and are less susceptible to hydrolysis. Sodium alginate and CMC are suitable for use in foodstuffs such as soy milk, which are close to neutral.

The influence of temperature on viscosity: As the temperature rises, the molecular movement is accelerated, the viscosity of the general solution is reduced, such as sodium alginate solution under the usual conditions of use, about 5-6 ℃ for every increase in temperature, the viscosity is reduced by 12%. The increase in temperature accelerates the rate of chemical reactions, especially under strong acid conditions, and most colloids hydrolyse much faster. When the polymer colloid depolymerisation, the viscosity drop is irreversible: in order to avoid the irreversible drop in viscosity, the colloid solution should be avoided for a long time at high temperature by heat. When a small amount of sodium chloride is present. The viscosity of xanthan gum changes very little in the range of -4 to +93°C. This is a special case in thickening agents. The thermal stability of xanthan gum and propylene glycol alginate is better with large bit resistance.

The effect of shear on the viscosity of the thickener solution: the viscosity of a certain concentration of thickener solution will change with the processing and transmission means of stirring and pumping.

Synergistic effect of thickeners: If thickeners are mixed and used in combination, a viscosity superposition effect will be produced between thickeners. This superposition can also be reduced, for example, gum arabic reduces the viscosity of yarrow gum. Sometimes the use of a thickener alone does not give the desired result and must be combined with some other emulsifier to give a synergistic effect. Thickeners with good synergistic effects are: CMC and gelatine, carrageenan, guar gum and CMC, agar and acacia bean gum, xanthan gum and acacia bean gum, etc.

Other factors on viscosity: In addition to pH and temperature on viscosity, there are many other factors that affect viscosity. Adding non-aqueous solvents or increasing the amount of solvents that are miscible with water (e.g. alcohol) to the sodium alginate solution increases the viscosity of the solution and eventually leads to the precipitation of sodium alginate. Whereas a high concentration of surfactant will reduce the viscosity of sodium alginate and eventually salt alginate out of solution, monovalent salts will also reduce the viscosity of dilute sodium alginate. Due to the different degrees of polymerisation, the relative molecular masses also vary greatly, so there is no accurate fixed relative molecular mass of thickeners, generally expressed in terms of the average relative molecular mass or relative molecular mass range.