Soy protein isolate process

Abstract: As a food additive, soy protein isolate is widely used in various food systems. The successful application of soy protein isolate is that it has a variety of functional properties. Functional properties are the most important physical and chemical properties of soy protein isolate, such as gelation, emulsification, color protection, viscosity, etc. This article mainly focuses on a preparation process of soybean protein.

Keywords: soy protein isolate, separation process, influencing factors, equipment

Related products for this article: soy protein isolate

Foreword: Soy protein isolate is an important plant protein product. In addition to nutritional value, it also has many important functional properties. These functional properties are of great value for the application of soybean protein in food. The functional properties of soy protein can be classified into three categories: one is the hydration property of the protein (depending on the protein-water interaction), the second is the property related to protein-protein interaction, and the third is the surface property. Hydration properties include: water absorption and retention, wettability, swelling, adhesion, dispersibility, solubility and viscosity. The interaction between protein molecules is of practical significance when soy protein undergoes precipitation, gelation, and the formation of various other structures (such as gluten). Surface properties mainly refer to emulsifying properties and foaming properties.

Isolated Soy Protein
  1. Functional characteristics

1.1 Emulsification

Emulsification refers to the ability of mixing oil and water to form an emulsion. Soy protein isolate is a surface active agent, which can reduce the surface tension of water and oil as well as the surface tension of water and air. Easily form a stable emulsion. The emulsified oil droplets are stabilized by the protein gathered 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 stability of the emulsification performance. In the production of baked food, frozen food and soup food, adding soy protein isolate as emulsifier can make the product state stable.

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 the 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 adsorption, 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 Swelling property refers to 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 to 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 Gelation (also known as gelation)

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, presence or absence of salt sulfhydryl compounds, sulfites or lipids. The higher the protein content, the easier it is to make a 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 the 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 products and improve their performance.

1.9 Organization

It refers to the process in which soy protein is processed, its protein molecules are rearranged and combined 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.

  1. Production process

2.1 Acid precipitation and alkali extraction

This is a traditional separation and extraction method. This method uses the characteristic of precipitation of most proteins in soybeans at the isoelectric point (pH 4~5) to separate them from other components. The precipitated protein is dissolved after adjusting the pH, so it is called acid precipitation and alkali extraction. The process flow is shown in Figure 1. The disadvantages of acid precipitation and alkali extraction are: acid consumption, large alkali consumption, high waste water treatment cost, and low product yield. The separation and extraction method needs to be improved. But it is still the basic method of industrial production.

2.2 Membrane separation method

According to the molecular weight and shape of the soybean protein and the adaptability of the membrane to the soybean protein, the membrane materials and membranes with different molecular weight cut-offs are selected to ultrafiltration separation and ultrafiltration purification of the soybean protein extract, so that non-retained components are eliminated to meet the standards. Separate the soy protein liquid, then ultrafiltration and concentrate the purified soy protein extract to the required concentration, then discharge, spray-dry into powdery soy protein isolate.

2.3 Reverse micelle extraction and separation method

Reverse micelles are an aggregate formed by surfactants in organic solvents, in which the non-polar tail of the surfactant is outside, contacts with the organic solvent, and the polar head is inside to form a polar nucleus, which has an aqueous solution. And the ability to solubilize proteins, so this organic solvent containing reverse micelles can be used to extract proteins from the aqueous phase. The main factors affecting the reverse micelle extraction process are the type and concentration of surfactants, the pH value of the aqueous phase, ionic strength, and temperature. The advantages of reverse micelle extraction technology are: high selectivity, convenient operation, easy amplification, extractant (reverse micelle) phase can be recycled, separation and concentration can be performed simultaneously. The disadvantage is that the protein is not stable in the existing reverse micellar system, resulting in a large loss of protein activity before and after extraction, thus restricting its industrial application.

2.4 Reversed-phase high performance liquid chromatography

This is a method for rapid separation of 7S and 11S globulins in soy protein. Under the conditions of a separation condition of 40℃ and a flow rate of 1 mL/min, the separation of the corresponding globulins can be completed in 9 minute

  1. Process technology plan

This program adopts alkali-dissolved acid precipitation method to prepare isolated protein.

3.1 Soybean pretreatment process

3.1.1 Process description: As the production process of edible soybean meal, the first requirement is that the impurity removal should be clean. It is necessary to remove organic impurities (such as roots, stems, leaves) and inorganic impurities (such as mud, stones, metal particles, etc.) in the oil. In addition, the lumps, diseases and insect pests, and mildew particles in the oil should be removed to ensure that the low-temperature meal meets the food-grade hygiene standards. In order to ensure the above requirements, the process combination should be reasonable, the cleaning should be distinguished according to the difference of the physical properties of oil and non-oil, and the non-oil material should be removed as much as possible to ensure product quality and product yield. In the pre-treatment process Part of the soybean hulls should also be removed. The soybean hulls contain a lot of colloids and pigments, and its presence will cause the color and non-product substance content of the products (such as soybean oil and protein isolate) to exceed the standard. Effective removal of bean hulls has a positive effect on the process and product quality. As a soybean pretreatment process for producing low-temperature soybean meal, the more important one is that while the soybean pellets are made into flake-shaped soybean greens, high-temperature heating cannot be used, and the water-soluble protein in the soybean greens cannot be denatured. Therefore, this process The design and selection of process parameters are extremely important. In the design of this process, the preservation rate of water-soluble protein is fully considered, and a reasonable soybean green sheet can be produced.

3.1.2 Main technological performance indexes:

Peeling rate: 97%

Green thickness: 0.3mm

Moisture content of green body: <9%

Powder degree of green body: less than 8% through 20 mesh sieve

3.2 leaching process

At present, looking at all kinds of oil preparation methods, the use of No. 6 solvent (the main component is ethane) to extract oil is a relatively advanced oil production process, which has been widely adopted in the world. However, compared with the comprehensive utilization of meal and oil after leaching, the current oil leaching process requires high-temperature heating in order to remove and recover the solvent from the meal while extracting the oil, which not only consumes a large amount of steam and condensing water, but also As a result, the precious plant protein in the meal is highly denatured, its own biologically active substances are destroyed, and the utilization value is reduced (only for feed and fertilizer). At the same time, the quality of crude oil decreases, and the consumption of steam and water is high. Solvent No. 4 is purified from liquefied petroleum gas, and its main components are butane and propane. The use of No. 4 solvent to extract grease is a brand-new grease extraction technology. The biggest advantage of this process technology is low-temperature desolventization, for which reason the vegetable protein in the obtained meal is almost unchanged.

3.3 Process description

3.3.1 Process

Soybean→primary cleaning→measurement→cleaning→drying→second-level specific gravity stone removal→iron removal→ ash removal→disintegration→crushing→vibration screening→wind sorting→softening→iron removal→rolling billet→drying→green billet→ To leaching

The vegetable oil blank (0.25mm~0.3mm) after the previous process is transported to each leaching tank through the conveying equipment. After removing the air, the oil in the blank is leached countercurrently with mixed oil and fresh No. 4 solvent. The high-concentration mixed oil is pumped into the mixing oil tank, and then the meal is desolventized, that is, the solvent gas in the meal is vaporized under reduced pressure and separated from the meal. The qualified meal is discharged from the extractor and sent to the meal through the conveying equipment. Library. The vaporized solvent gas is compressed by the compressor, condensed and liquefied by the condenser, and recovered to the solvent tank for recycling. Using the low boiling point of the solvent to evaporate the mixed oil and evaporate the solvent, the purpose of separating the oil and the solvent has been achieved. The mixed oil in the mixed oil tank is pumped into the evaporator (rising film type). In this process, the solvent gas is continuously heated to vaporize from the mixed oil, which is also compressed by the compressor. During this process, the solvent gas is continuously heated to vaporize the solvent gas from the mixed oil, which is also compressed by the compressor and then passed through the condenser. After condensing and liquefying, it is recycled to the solvent tank for recycling.

Process diagram:

Flow chart

3.4 Protein separation process

Protein isolate is also known as isoelectric point protein powder. It is a refined soy protein product obtained by further removing non-protein components from dehulled and defatted soybeans. Compared with protein concentrate, protein isolate not only removes soluble carbohydrates, but also requires the removal of insoluble polysaccharides. Therefore, the protein content is high (not less than 90%), but the yield is inevitably lower.

3.4.1 Production principle

Most of the protein in low-temperature defatted soybean meal can be dissolved in dilute alkali solution. After extracting the low-temperature defatted soybean meal with dilute lye, centrifugal separation can remove the insoluble matter (mainly polysaccharides and some residual protein) in the soybean meal, and then adjust the pH value of the extract to about 4.5 with acid, the protein is at a constant temperature. Agglomerate and settle down in the state of electric points, and the protein precipitate can be obtained after separation, and then the separated soybean protein can be obtained by washing, neutralizing and drying.

3.4.2 Production process

Add low-temperature defatted soybean meal powder (soybean meal requires no mold, low skin content, low impurities, protein content above 45%, and protein dispersion index above 80%) into the extraction tank for dissolution, adding 15 times the weight The water dissolves, and the dissolution temperature is generally controlled at 55~80 degrees. The dissolution time is controlled within 120 minutes. Add NaOH solution in the extraction tank and adjust the PH value of the extract to between 7 and 9.5. The extraction process requires constant stirring. The stirring speed should be 30 to 35 revolutions per minute. .

After dissolving in the extraction tank, the protein solution is sent to a centrifuge to separate and remove insoluble residues. In order to enhance the separation effect of the centrifugal separator, the dissolving liquid can be passed through a vibrating screen to remove the coarse residue. The separated protein solution flows into the acidification tank, and the hydrochloric acid solution is added to adjust the PH value to 4.5. At this time, a large amount of protein precipitates out at the isoelectric point. When adding acid, it needs to be stirred continuously, and the pH value should be continuously measured. When all the solutions have reached the isoelectric point, immediately stop stirring and stand still for 20-30 minutes to allow the protein to form larger particles and precipitate. The faster the precipitation speed, the better. The general stirring speed is 30-40 rpm. The centrifuge dewaters the precipitate deposited by the acid by centrifugation and discards the clear liquid. The solid part flows into the washing tank and is washed with water. The pH value of the protein solution after washing is about 6, and the washed protein slurry is sent to the centrifuge. Excess waste liquid is removed from the medium, the solid part flows into the dispersion tank, and alkali is added to dissolve it, and the pH is controlled at 6.5-7.0. The separated soybean protein slurry is heated at 90 degrees for 10 minutes or 80 degrees for 15 minutes, which can not only sterilize Function, and can significantly improve the gel properties of the product. Use a high-pressure pump to pump the protein liquid into the spray dryer for drying. The concentration is generally controlled between 12% and 20%. Because the concentration is too high, the viscosity is too high, it is easy to block the nozzle, and the spray tower is unstable; the concentration is too low, the product The particles are small and the specific volume is too large, which is unfavorable for application and transportation. In addition, the spraying time is prolonged and energy consumption is increased.

The above alkaline extraction and acid precipitation process can effectively purify protein to more than 90%, and the product quality is good and the color is light. The process is simple and easy to implement, and the production and operation are easy. It is a very mature protein isolate production process at home and abroad. The quality of soybean meal directly affects the quality and yield of protein isolate. Only high-quality soybean meal can obtain high-quality and high-yield protein isolate. Soy meal requires no mold, low skin content, low residual solvent content, and high protein content. (Especially low-denatured eggs), low fat content, soybean meal should be crushed and passed through a 40-60 mesh sieve. The more water you add, the higher the protein dissolution rate and extraction efficiency. However, if you add too much water, you need to increase equipment investment, and the separation time is long, and acid precipitation is difficult. It is not applicable from an economic point of view. Generally, water is controlled. The amount is 12-20 times. The increase in the temperature of extracting soybean protein can only increase the extraction rate, and has little effect on the yield of soybean protein. When the temperature is too high, the viscosity increases, separation is difficult, and the protein is volatile, which affects the process performance of the product and consumes too much energy. Many, generally the temperature is controlled at 55~80 degrees.

The extraction time mainly affects the protein dissolution rate. Under certain conditions, the longer the time, the higher the dissolution rate. Generally, the dissolution time increases steadily in the first 30 minutes from the perspective of nitrogen solubility, and reaches a flat and stable state in the last 45 minutes. Comprehensive indicators, the general dissolution time from the perspective of nitrogen solubility increases steadily in the first 30 minutes of separation, and reaches a flat and stable state in the last 45 minutes. Therefore, the general leaching time does not exceed 120 minutes in terms of comprehensive indicators.

When the pH is greater than 7, the dissolution rate of undenatured protein increases with the increase in pH, but the pH value should not be too high. According to the data, due to the long-term action of soybean protein under strong alkali conditions, it will play a “cyst-lay reaction”, making it useful The amino acids are converted into toxic compounds, resulting in products of inferior quality and loss of edible value. Therefore, the PH value is generally controlled between 7.0 and 9.5.

3.5 Refining process

3.5.1 Process description

As far as the production process is concerned, currently the continuous production process of Alfa-Laval in Sweden is generally used, and some of the production processes are from West De West-Varia or CIB in Italy. However, the above-mentioned companies The production process is basically the same, and only maintains their own technical characteristics in some details. This process adopts internationally advanced process technology, which has matured after improvement in recent years. It has the following advantages:

A. The degumming process adopts a butterfly centrifuge for continuous hydration and degumming, and continuous demelting and drying.

B. The decolorization section will adopt the most advanced pipeline continuous decolorization process (digestion and absorption project), which makes the mixing and decolorization time of decolorizer and grease basically consistent. The entire decolorization process works under positive pressure to prevent oxygen and air in the air. Hot oil contact, a pump is in place.

C. The continuous desolventization, drying and deodorization section adopts the membrane-packed deodorization tower of German FH Company. The tower has obvious physical refining characteristics and can be adapted to direct refining of non-glue grease with acid value below 10 into high-grade cooking oil .

3.5.2 Process advantages

A. High refining rate

Because the quality of crude oil is relatively good, and continuous refining and filling vacuum drying are used, the refining rate from crude oil to secondary oil can reach 98%; the decolorization process is efficient, simple and convenient to operate, and the quality of the oil is good (acid value Less recovery, low peroxide value), compared with tank type or tower type decolorization, it can save white clay up to 40%, and the corresponding decolorization and refining consumption is low; the product separated by the physical refining process used in deodorization is directly high cooking oil fatty acid, Correspondingly reduce the refining consumption, and increase the refining rate by 0.5% relative to the neutralization method for each acid value

B. The quality of oil is good. Continuous refining is completed in sealed equipment, the chance of contact with air is reduced, the oxide in the grease is greatly reduced, and the color is greatly improved.

C. Energy saving

Due to the packed dryer and packed deodorizing tower, only these two parts can save 40% of steam.

D. Concise craftsmanship