Influencing Factors Of Food Thickener

Effect of structure and relative molecular weight on viscosity: General thickener is a kind of colloid which is easy to form network structure or has more hydrophilic groups in solution, and has high viscosity. Therefore, the viscosities of thickeners with different molecular structures may be quite different even at the same concentration and under other conditions. With the increase of average molecular weight of the same thickener, the probability of forming network structure also increases. Therefore, the viscosity of thickener is closely related to the relative molecular weight, that is, the higher the relative molecular weight, the greater the viscosity. The viscosity of food decreases in the process of production and storage, which is mainly due to the degradation of thickener and the decrease of relative molecular weight.

The effect of concentration on viscosity: with the increase of thickener concentration, the volume of molecular elasticity of thickener increases, the probability of interaction increases, and the amount of water molecules adsorbed increases, so the viscosity increases.

The effect of pH value on viscosity: the pH value of the medium is closely related to the viscosity and stability of thickener. The viscosity of thickener usually changes with pH value. For example, when sodium alginate is in pH 5-10, the viscosity is stable; when the pH value is less than 4.5, the viscosity increases obviously (but under this condition, the viscosity is unstable due to acid catalytic degradation, so it is better to be used under near neutral conditions). When the pH value is 2-3, propylene glycol alginate shows the maximum viscosity, while sodium alginate precipitates. The viscosity of gelatin is the lowest at the isoelectric point, but the change of pH value of xanthan gum (especially in the presence of a small amount of salt) has little effect on the viscosity. The hydrolysis of polysaccharide glycoside bond is carried out under the condition of acid catalysis. Therefore, in the food with strong acid medium, the straight chain sodium alginate and the carboxymethyl cellulose sodium with smaller side chain are easy to degrade, resulting in the decrease of viscosity. Therefore, it is advisable to select the glyceryl alginate and xanthan gum with larger or more side chains, higher steric hindrance and less hydrolysis in soft drinks and yoghurt with high acidity. However, sodium alginate and CMC should be used in soybean milk and other neutral foods.

The effect of temperature on viscosity: with the increase of temperature, the speed of molecular motion is accelerated, and the viscosity of general solution decreases. For example, for sodium alginate solution under normal conditions, the viscosity decreases by 12% every 5-6 ℃ increase of temperature. With the increase of temperature, the speed of chemical reaction is accelerated, especially in the condition of strong acid, the hydrolysis rate of most colloids is greatly accelerated. When the polymer colloid depolymerization, the decrease of viscosity is irreversible. In order to avoid the irreversible decrease of viscosity, it is necessary to avoid heating the colloid solution at high temperature for a long time. In the presence of a small amount of sodium chloride, the viscosity of xanthan gum changes little from - 4 ℃ to + 93 ℃, which is a special case of thickener. Xanthan gum and propylene glycol alginate have good thermal stability.

The effect of shear force on the viscosity of thickener solution: the viscosity of thickener solution with a certain concentration will change with the processing and transmission means such as stirring and pump pressure.

Synergistic effect of thickeners: if thickeners are mixed and mixed, thickening agents will produce a viscosity superposition effect, which can be synergistic. After a certain period of time, the viscosity of the mixture is greater than the viscosity of each component, or a higher strength gel is formed. For example, gum arabic can reduce the viscosity of tragacanth gum. Sometimes, only one thickener can not get ideal results, so it must be used with other emulsifiers to play a synergistic effect. The results showed that the synergism of thickener was CMC and gelatin, carrageenan, guar gum and CMC, agar and Robinia bean gum, xanthan gum and Robinia bean gum.

The influence of other factors on viscosity: in addition to pH value and temperature, there are many factors that affect viscosity. The viscosity of sodium alginate solution will be increased by adding non-aqueous solvent or increasing the amount of solvent (such as alcohol) which can be miscible with water, and eventually lead to the precipitation of sodium alginate. However, high concentration of surfactant will reduce the viscosity of sodium alginate, and eventually make alginate salt out of the solution, and monovalent salt will also reduce the viscosity of dilute sodium alginate. Due to the different degree of polymerization, the relative molecular weight also varies greatly, so the thickener has no accurate fixed relative molecular weight, which is generally expressed by the average relative molecular weight or the relative molecular weight range.