Food glue is generally water-soluble macromolecules, dissolved in water has a greater viscosity, so that the food system has a thick sense, can be used as pie filling, drinks, jams, etc., fillers, pet food adhesive, but also can be used to hang the adhesive icing (such as cake), glazing (such as coffee), frosting (such as frosting of cakes).

Food gums can generally be dissolved or dispersed in water to produce the effect of thickening or increasing the viscosity of the fluid. And all food gums generally have a thickening effect, which is the main reason it can be widely used, in addition, the rheological properties of various colloids also tend to vary, and this rheological properties of the food being applied is critical, will directly affect the sensory quality of the food. Therefore, when selecting a colloid for the development of a food product, the rheological properties of the colloid are the first factor to be considered.

All hydrocolloids have a certain viscosity, with a thickening effect, when the hydrocolloid molecules undergo hydration. Of course the thickening effect is not the same for different types of food gums. Most food gums can obtain high viscosity fluid at very low concentration (e.g. 1%), but there are some colloids that can only obtain lower viscosity fluid even at very high concentration.

In addition, in general, food gums that tend to form a reticulated structure in solution or have more hydrophilic groups have a higher viscosity. The higher the molecular weight of the same food glue, the higher the viscosity of the system with the same mass concentration. As the concentration of the food glue increases, the viscosity will increase more or less.

The viscosity of ionic food glue is more affected by the electrolyte and pH of the system than that of non-ionic food glue. For example, the viscosity of sodium alginate is stable at pH 5-10, and the initial viscosity increases significantly when the pH is less than 4.5, while the molecules of alginic acid undergo acid-catalyzed degradation, and the viscosity gradually decreases, and the alginic acid precipitates when the pH further decreases to 2-3; however, propyleneglycol alginate, because it does not contain carboxyl groups in the molecule, not only does not produce precipitation, but also has the maximum viscosity.

It has strong resistance to acidity and salt precipitation. Polymer with more side chains, such as xanthan gum, due to its special structure, has a unique resistance to acid, alkali and electrolyte properties.

Foodstuffs generally have a decrease in viscosity when the temperature rises, and a rise in viscosity when the temperature falls. Many macromolecules are degraded at high temperatures, especially under acidic conditions, and the viscosity will drop permanently.

Factors affecting the fluid properties of food glue

The rheological properties of food glue solution and viscosity and shear rate has a direct relationship, all the food glue and fluid-type food rheological properties can be divided into Newtonian fluid and non-Newtonian fluid two kinds of basic rheological system, the former viscosity does not change with the change in shear rate, while the latter viscosity with the change in shear rate will change. As for most of the food glues, they are non-Newtonian fluids.

Factors affecting the fluid properties of food glue include: viscosity properties, concentration, temperature, molecular weight, shear rate, shear force, coexisting ions and coexisting components, etc. These factors are often not independent of each other in affecting the fluid properties of food glue, often interacting with each other, interrelated.

(a) Viscosity and concentration
Food glue fluid viscosity and concentration is inseparable from each other, generally with the rise of food glue concentration, fluid viscosity will increase significantly, but the two are not linear relationship. In low concentration, some food glue fluid can show Newtonian fluid characteristics, but with the increase of food glue concentration, its rheological properties gradually turned to non-Newtonian fluid, the specific performance is: fluid viscosity with the increase of the shear rate and obviously reduce, for example, for low viscosity type of sodium carboxymethyl cellulose (CMC), in its solution concentration is low (below 3%), the fluid can show good Newtonian fluid However, as the concentration of CMC increases, the fluid characteristics gradually show non-Newtonian fluid type (Figure omitted). However, for high molecular weight and high viscosity CMCs, the gel concentration is only non-Newtonian even at very low concentrations.

(ii) Temperature
As the temperature of the solution increases, the viscosity of most food gels decreases significantly, which is similar to the decrease in the concentration of food gels described above, and as mentioned above, a large portion of the food gels are Newtonian fluids at low concentrations, whereas when the temperature of the gels is increased, the original non-Newtonian fluid will be transformed into a Newtonian fluid.

(iii) Molecular weight
The molecular weight distribution of food glue is also important for the fluid properties of the glue. Under other conditions, two different molecular weight distribution of food glue if the shear rate is zero, the viscosity of the same, but in the case of higher shear rate, they tend to show different fluid properties. In general, at low shear, food gums with broader molecular weight distributions tend to exhibit non-Newtonian fluid characteristics. Food gels with sufficiently long and intertwined molecular chains also often exhibit non-Newtonian fluid properties. Other factors affecting molecular weight include the average molecular weight, the chemical structure of the polymer, and co-existing components.

(iv) Shear Rate and Shear Force
Shear rate and shear force parameters are also important factors affecting the non-static rheological properties of food glue. Some food glue in the low shear rate presents Newtonian fluid characteristics, but in the high shear rate, the glue will become non-Newtonian fluid type.CMC, ammonium alginate and other food glue have this fluid change characteristics.

The relationship between the rheological properties of food glue and food taste

Various food glue rheological properties and application of the colloid with the sensory quality of food has a great relationship with the consumer is mainly the texture or taste of food, the use of food glue food will sometimes have a viscous texture, which is less willing to accept the consumer, specifically: viscous, not easy to dilute and dissolve the oral saliva, and even difficult to swallow. This texture characteristics and the use of food glue viscosity, shear thinning and other rheological properties are directly related.

Research shows that the food glue if the Newtonian fluid characteristics, this makes people unpleasant sticky taste often manifested in the food, and when the glue for the non-Newtonian fluid and has a strong shear thinning ability (as the shear rate increases, the viscosity value gradually decreases), the use of the food glue of the food often does not produce a sticky taste. And produce smooth taste, so different kinds of food glue used in the same food to obtain the taste will have obvious differences, the reason for this difference may be with the dispersion of the particles, molecular weight, molecular properties, molecular chemical bonding within the role of the strength of the colloid itself factors.

This relationship between the fluid properties of food colloids and the taste of food is more prominent in low-sugar or low-calorie foods, which generally add artificial sweeteners and often replace digestible sugar compounds such as starch and dextrin with low-calorie food colloids, which play the role of filling and thickening, so for this type of food, the rheological properties of the colloid are more important than the application of the food in the sugar-based materials, i.e. For example, when colloids such as guar gum and CMC are applied in these foods, when they are added to the foods at a fluid characteristic concentration that exhibits shear-thinning properties, a pleasant mouthfeel is more likely to be obtained, rather than a sticky mouthfeel.

In addition, when people chew food with their tongues and teeth, a certain shear force or shear rate will be generated, and thus when eating fluid food such as beverages added with food gums, the viscosity and other fluid properties of such food will also be affected, and thus will also directly affect the evaluation of the taste of food by consumers, which is a point that should be taken into account in the development of the new type of fluid food.