Soybean is one of the main crops in China. Not only can it be used to extract edible oil, but its rich soybean protein is an important source of plant protein. There are many types of soy protein commonly used in food processing, such as soy protein isolate, soy protein concentrate, and soy protein. Among them, soybean protein isolate (SPI) is a kind of full-priced protein produced under low-temperature conditions with defatted soybean meal as raw material, with a protein content of more than 90%. SPI has the characteristics of no cholesterol, rich nutrition, low price, and easy availability, and contains a variety of amino acids needed by the human body. It can be applied to the food industry as an animal protein substitute and has great development potential.
The production process and technology of soybean protein isolate abroad have developed rapidly, and a series of formula technologies have been formed from extraction methods to modification methods. According to different product application fields and product properties, the extraction methods and modification methods are different. The products thus produced are widely suitable for the different needs of meat, dairy products, light chemical industry, and other fields, and truly reflect the high nutrition and high value-added characteristics of soybean protein.
However, natural SPI is difficult to meet the requirements of food industry production. SPI is easily denatured under certain extreme conditions, and the denatured protein will further form water-insoluble aggregates or even precipitate, resulting in poor solubility.
SPI can form a hybrid gel with myofibrillar protein (MP) in meat under certain temperature conditions. Studies have shown that mixing natural SPI with meat products will reduce the gel properties of the finished product. This is because in the production, the core temperature of meat products is around 70 ℃, and the 7S and 11S proteins, the two most important proteins in SPI, have not yet been denatured at this temperature. At this time, the MP has reached the denaturation temperature and the gel has begun to form. In the process of gel formation, it is necessary to continuously absorb water, which leads to a loose structure and poor elasticity of the composite gel, which limits the ability of SPI to improve the texture-related properties of the MP gel. Modification of SPI can improve its functional properties and expand its application range in the production and processing of meat products.
1.The main functional characteristics of modified soy protein isolate in meat processing.
MP is a salt-soluble protein that plays a major function in the production and processing of meat products. It can endow meat products with many ideal physical and chemical properties. In the food industry, SPI can not only be added to meat products as a non-functional filler but also can use its function as an additive to mix with myofibrillar protein to improve the quality of meat products.
1.1. Water Holding Capacity
Water holding capacity is an important indicator for testing the quality of meat products in production and processing. Because the three-dimensional network structure of the protein can lock the water in the muscle tissue. In addition, the hydrophilicity of the polar groups on the SPI peptide chain can preserve meat juices during the production of meat products, which improves the quality and productivity of meat products.
Yuxiang Ma and others made a mixed gel with SPI and salt-soluble muscle protein. After SPI high-temperature treatment, the ultrastructure of the composite gel becomes rough but the water holding capacity is significantly improved. Low-field NMR technology can study the moisture distribution of mixed proteins. After adding modified SPI and carrageenan, the water loss rate of the meat emulsion gel is reduced, and the water-holding capacity of the mixed gel is improved.
1.2. Emulsification
Emulsification and emulsion stability refers to the ability of water and oil to mix to form an emulsion, which is also an important index for evaluating meat quality. The addition of SPI to meat products can prevent the leakage of fat in meat emulsion products, improve the structure of the product, and improve the emulsification of meat products. In processed meat products, the emulsification effect of modified SPI can be enhanced, and the nitrogen soluble index (NSI) determines its emulsification. When the NSI is 80%, it is beneficial to improve the emulsification effect of SPI in meat products.
Jinwu He and others added natural SPI and glycosylated SPI to carp myofibril protein. Compared with natural SPI, the SPI treatment after glycosylation significantly improved the emulsification of the mixed protein.
Lianzhou Jiang and others studied the emulsification changes of SPI after ultrasonic treatment mixed with pork MP. The emulsification activity and emulsification stability of the composite system after 400 W and 20 min treatment are the best.
Jing Liang and others studied the emulsification changes of the modified SPI and myofibril protein blend system, and the results showed that thermal modification can improve emulsification activity, followed by alkali modification, but ultrasonic and radiation modification effects are not obvious.
The SPI after the high-temperature modification treatment at 95 ℃ can significantly improve the emulsification of the composite system.
3. Gelation
In a high-pressure or high-temperature environment, myofibrillar protein molecules are denatured first and then aggregated into a network structure. Water and fat are wrapped. This is the process of gel formation. In the process of myofibril protein gelation, the cross-linked and mixed proteins can only form protein particles that are not elastic. Only when the proteins are connected in an orderly manner can the formed gel be elastic.
After the pork is slaughtered, excessive air oxidation will increase the pores of the gel, resulting in a decrease in the strength of the gel and a decrease in the water holding capacity of the pork. SPI can form a gel when heated, so SPI is often added to meat products to improve the gel properties of meat products.
Feng and others added SPI after high-temperature treatment at 90 ℃ to myofibrillar protein. The results showed that SPI can be modified to increase the hydrophobic force. After mixing with myofibril protein, it can significantly enhance the elasticity and hardness of the mixed protein gel. , Unmodified SPI will reduce the gel strength.
Lin Meng studied the effect of high pressure on the physicochemical properties of low-sodium pork minced meat by the combination of SPI and potassium chloride. With the increase of pressure level, the hardness and elasticity of pork minced meat and the cooking loss rate increased significantly, reaching the highest at 200 MPa, which is OK. Improve the quality of low-sodium minced pork products.
Jiang and others used the extreme pH environment of pH12 and pH1.5 to treat the SPI and myofibrillar protein hybrid gel, and found that its hardness was similar to that of the gel with transglutaminase added, and was significantly higher than that of the heat-treated hybrid gel.
Bo Wang and others compounded glycosylated SPI with myofibrillar protein in different ratios. The results showed that the gel hardness and elasticity of the mixed protein gel after glycosylation were significantly higher than that of the natural SPI mixed protein, and the microstructure was also more uniform and dense, but the whiteness value decreased.
Lingdi Wang treated SPI with high temperature and transglutaminase to prepare a mixed protein gel with MP. The results showed that transglutaminase can promote the cross-linking of SPI and MP to form a polymer, which is beneficial to improve the elasticity of the mixed gel.
Mingcheng Zhang studied the two methods of enzymatic hydrolysis and enzymatic cross-linking to process SPI to add it to meat emulsion. The results show that the meat emulsion cross-linked with transglutaminase after papain hydrolysis has a uniform tissue state. After heating, a dense gel network can be formed, and the hardness, resilience, and chewiness of the product are significantly increased.
2. Application of modified soy protein isolate in meat products.
Modified SPI is used in meat products to increase flavor, prevent gravy separation, improve the quality of meat products, and extend shelf life.
2.1. Pieces of Meat Products
Pieces of meat products usually refer to large pieces or whole pieces of meat products. But its integrity is easily damaged during processing. By adding modified SPI, syneresis can be reduced, tissue characteristics can be improved, and product quality can be improved. The use of modified SPI can not only maintain the appearance and moisture of meat products due to its excellent water retention and gel properties, but also use its natural oxidation resistance as a coating material. Delay the oxidation of meat products, extend the shelf life of food while maintaining the sensory quality of meat products.
2.2. Minced Meat Products
Meatloaf, meatballs, and surimi products are all minced meat products. The combination of lean meat and fatty meat to form a stable meat emulsion is the key to determining its production quality. Because SPI has good water and oil absorption, it can combine lean and fatty meat to improve nutritional value and product yield. Yang Zhou and others added egg white powder and soy protein isolate powder in the process of making fish balls. SPI can significantly enhance the gel strength of fish balls and improve the quality of fish balls. Li and others studied the color, emulsification stability, and rheology of pork minced pork after high-pressure treatment of soy protein isolate. The results show that SPI after high-pressure treatment can improve the emulsification properties of pork meat.
2.3. Emulsified Meat Products
Emulsified meat products mainly refer to sausages and hams. SPI can form a stable emulsification system with salt-soluble proteins in meat, especially myofibrillar proteins. The excellent emulsifying properties of SPI can prevent the oil from oozing out caused by the accumulation of fat in the meat emulsion, and improve the oil retention of meat products. Gives high-quality taste and flavor to products such as emulsified sausages. Paglarini and others used ultrasonically modified SPI, carrageenan, and inulin as raw materials to prepare Frankfurt intestines. The results show that the modified SPI can reduce animal fat intake and improve the taste of the product.
2.3. Imitation Meat Products
SPI is often used as a raw material to replace animal protein because of its good emulsifying and gel properties. SPI is under the combined action of multiple factors through processes such as extrusion. Protein, fat, and carbohydrates will undergo complex changes, which can imitate the taste and flavor of natural meat. Because of its high nutritional value and unique flavor, it is popular among vegetarians. Zhongwen Mo studied the use of molecular recombination technology to structure soybean protein. The results show that the protein can have a lean fibrous tissue structure. The prepared imitation meat food tastes good, and the shelf life is more than 6 months.
3. How to use soy protein isolate.
Soy protein isolate has been widely accepted by most manufacturers in various combined use methods. Especially the chopper method is the most popular. The main reason is that it has many functions and the manufacturing process is more flexible. With regard to its application today, compare the advantages and disadvantages of the following application methods.
3.1. Rehydration
First, put the soy protein isolate with 4 to 5 times ice water into the chopper and chop at high speed for 1 to 2 minutes. Then, add lean meat, ice water, polyphosphate, and salt, and chop at high speed for 2 minutes to extract salt-soluble meat protein. At this time, the temperature is just controlled at 2～4℃, because this temperature is the most suitable temperature for extracting salt-soluble protein. After the soluble protein is extracted, add fat and ice water, and continue to chop for 2 minutes. At this time, the temperature should be around 6-8°C. This is the most common method.
3.2. Gel Method
First, use 4 times the soy protein isolate water, use a chopper to emulsify it at high speed, and then wait for it to be used. The other steps are the same as the above-mentioned rehydration method. In addition, the gel method can be stored in a refrigerator for later use. Although the protein isolate can be stored in the refrigerator for 2 to 3 days, it is prone to rancidity and easy growth of bacteria, so it is recommended to use it up as soon as possible.
3.3 Injection Method
Small pieces of meat no more than 6 cm can be added with soy protein isolate by rolling and kneading, and for some larger meat products, the injection can be used. Dissolve the modified SPI in saltwater, and then inject the solution into the meat. The marinating liquid can be evenly dispersed in the meat, shortening the marinating time and increasing the product yield.
3.4. Emulsified Oil Method
The emulsified oil produced by protein isolate can use chicken skin, fat fat, tallow, soybean oil, and pigskin as raw materials. The most important method of making emulsified oil is to rehydrate the protein isolate with a chopper and then add oil, and continue to chop into emulsified oil before use. In the production process of emulsified products, the emulsified oil is added after the salt-soluble meat protein is extracted, which is more complicated than the gel method. However, proper processing and addition of emulsified oil can not only reduce product cost, but also increase product fragrance and flexibility.
3.5. Dry Addition
This method is simple to use, first add the protein isolate to the lean meat and chop it slightly. Add 4 times more water, chop and mix for 1 to 2 minutes, then add polyphosphate, ice water, and salt, and continue to chop for 2 minutes. There is also a method of directly adding dry matter such as protein isolate and starch to the final chopping. Although this method is convenient, it is not recommended to use. Because the soy protein isolate cannot be fully rehydrated and its function is not fully developed. The product will be softer under the same formula, and the water absorption and oil retention will be poor. Therefore, this method is not recommended. . Another example: adding soy protein isolate and lean meat together, but without rehydration, this effect can not rehydrate the soy protein isolate properly, but also affects the extraction of salt-soluble protein, and the manufactured product will be softer. Therefore, the rehydration and addition steps also affect the quality of the final product.
Due to the impact of the performance of the isolated protein itself. A certain reversible reaction will occur in the case of salt, which will weaken its emulsification, oil retention, and water retention properties. Therefore, no matter what method is used to produce emulsified meat products, in order to maximize the functionality of soy protein isolate, soy protein isolate must be completely rehydrated.
