1.1　emulsification

Emulsification refers to the ability of mixing oil and water to form an emulsion. Soy protein isolate is a surfactant, it can not only reduce the surface tension of water and oil, but also reduce the surface tension of water and air. Easily form a stable emulsion. The emulsified oil droplets are stabilized by the protein accumulated on the surface of the oil droplets, forming a protective layer. This protective layer can prevent the accumulation of oil droplets and the destruction of the emulsified state, and promote the stable emulsification performance. In the production of roasted food, frozen food and soup food, adding soy protein isolate as emulsifier can stabilize the product state.

1.2　 Hydration

Soy protein isolate contains many polar groups along its peptide chain backbone, so it has water absorption, water retention and swelling properties.

1.2. 1　 water absorption

Generally refers to the adsorption capacity of protein to water, which is closely related to water activity, pH, depth, protein particle size, particle structure, particle surface activity and so on. With the increase of water activity, its water absorption changes fast-slow-fast.

1.2. 2　 water retention

In addition to water absorption, soybean protein has the ability to retain water during processing, and its water retention is related to viscosity, pH, ionization strength and temperature. Salts can enhance protein water absorption but weaken the water retention of protein isolates. The maximum water retention capacity is 14g water/g protein at pH=7 and temperature 35～55℃.

1.2. 3　Expansibility

Swelling is the expansion effect of protein, which means that protein will swell after absorbing water. It is significantly affected by temperature, pH and salt. Heat treatment increases the swelling of soy protein. It is best at 80℃, and the swelling is basically close between 70～100℃.

1.3 　 oil absorption

1.3. 1 Promote fat absorption

The function of protein isolate to absorb fat is another form of emulsification. When protein isolate is added to meat products, it can form emulsion and gel matrix to prevent fat from moving to the surface, thus it plays a role in promoting fat absorption or fat binding. It can reduce the loss of fat and juice during meat product processing and help Maintain the stability of the shape. Oil absorption increases with the increase of protein content, and decreases with the increase of pH.

1.3. 2　 Control fat absorption

Protein isolate can also play a role in controlling fat absorption under different processing conditions. For example, it can prevent excessive absorption of fat during frying. This is because protein is denatured by heat and forms an oil layer on the surface of fried noodles.

1.4 　 Gelling (also known as gelling)

Refers to the ability of protein to form a colloidal structure. It enables the protein isolate to have higher viscosity, plasticity and elasticity. It can be used as a carrier for water, as well as a carrier for flavors, sugars and other complexes, which is extremely beneficial to food processing. The dispersed substance of soybean protein can be heated, cooled, dialysis and alkali treatment to obtain gel. Its formation is affected by the concentration of solids, speed, temperature and heating time, cooling conditions, the presence or absence of salt sulfhydryl compounds, sulfites or lipids. The higher the protein content, the easier it is to make strong, tough and elastic Hard gels, and the protein content is less than 70%, can only be made into soft and fragile gels.

1.5 Solubility

Solubility refers to the ability of protein to dissolve in an aqueous solution or salt solution. The degree of dissolution is called solubility. Solubility usually refers to water solubility. Proteins with good solubility must have good functionality, with good gelling, emulsifying, foaming and lipoxygenase activity. They are easy for food processing and utilization, and it is easier to blend into foods. The solubility of soybean protein is greatly affected by the heating treatment of raw materials, the amount of water added during dissolution, pH, and coexisting salts.

1.6 Foaming

Foaming property refers to the increase rate of the volume of soy protein in processing, which can play a role in crisping. Foam is composed of air dispersed in liquid or semi-solid phase. It is composed of many air droplets wrapped in a layer of liquid surface-activated soluble protein film, which reduces the surface tension of air and water. Bubbles are due to elasticity. The liquid film or semi-solid film is separated to prevent the merger of bubbles.

1.7 Stickiness

The viscosity of protein refers to the internal friction that appears when the liquid flows, also known as fluidity. It is important in adjusting the physical properties of food. The viscosity of protein solution is affected by the molecular weight, friction coefficient, temperature, pH, ionic strength, processing conditions and other factors of the protein. These factors can change the morphological structure, association state, hydration degree, swelling degree and viscosity of protein molecules. After soy protein isolate undergoes alkali, acid or heat treatment, its swelling degree and viscosity increase. The apparent viscosity of the soy protein solution increases exponentially with the increase of protein concentration, and is related to the swelling degree of the sample.

1.8 clumping

It means that when soy protein isolate is mixed with a certain amount of water, it can be made into a dough-like substance. This property can be used in the processing of flour products, such as bread and cakes, to increase the protein content of the product and improve its performance.

1.9 Organization

Refers to the process in which soy protein is processed and its protein molecules rearrange and combine to have a directional structure and form a fibrous protein similar to meat after solidification.

1.10 Conjunctival

It means that after soy protein and water form a dough, after high-pressure cooking, a film is formed on the surface. This film is a barrier between water and water-containing agents, which is a feature of soy protein suitable for intestinal processing needs. After the meat is chopped, it is coated on the fiber surface with a mixture of protein isolate and egg protein to form a film, which is easy to dry, can prevent odor loss, is conducive to the rehydration process, and provides a reasonable structure for the rehydration product.

1.11 Toning

Refers to the bleaching and color-increasing effects of soy protein isolate on products.