Twin-screw soybean protein puffing process
Soybean texture protein is a soybean product made from low-denatured defatted soybean meal, concentrated soybean protein and isolated soybean protein, with uniform tissue characteristics and specific tissue structure. Soybean tissue protein is also called artificial meat and vegetable meat (1.0kg soybean tissue protein is equivalent to 3.3kg pork), its main components are protein and carbohydrates, and its production methods mainly include fiber spinning method, steam tissue method, extrusion Puffing method, pressure organization method, etc.
Extrusion Technology of Soybean Tissue Protein
1.1 Technological process Low-denatured soybean meal → milling → storage → weighing (ingredients) → mixing → puffing → granulation → drying → packaging Add water and steam
2. The puffing principle
The extruder integrates various operations such as conveying, mixing, heating, and pressurizing, and can realize the mixing and transformation of materials in a very short time. After the low-denaturation defatted soybean meal is pretreated, it is fed into the extruder by the feeding auger. The material composed of protein and polysaccharide moves forward by the action of the rotating screw, and passes through a sleeve, under the action of high temperature, high pressure and strong shearing force. The material is converted into a viscous state, and then is instantly depressurized to a normal pressure environment through a precise continuous outlet mechanism, and the water in the high-pressure superheated state is rapidly vaporized and evaporated, resulting in a situation similar to an explosion. The material presents a microporous structure, and the cooled The proteoglycan mixture has a highly swollen tissue structure, the soy tissue protein. When the soybean tissue protein is rehydrated at about 60°C, it can absorb 1.5 to 3.0 times (weight) of water to form a fibrous sponge and an elastic structure with the same chewiness as meat. Stable products of different specifications can be used to make meatballs, wonton fillings, bacon, sausages, etc. It is used abroad to make minced meat for hamburgers, fruit tea, etc. Recently, artificial meat skewers made of it have appeared in the domestic market.
Factors Affecting Puffing and Determination of Process Conditions
3.1 Influence of raw materials on puffing
a. The effect of fiber
The raw material contains a certain amount of fibers. The presence of fibers reduces the extruded material, and at the same time, it also acts as a bridge in the internal structure of the extruded material, which is beneficial to increase the strength of the extruded material. However, due to its relatively small specific gravity, it is difficult to Mixing, when passing through the pressure relief port, causes irregularities in the shape of the extruded product. In practice, the fiber content of the raw material is controlled below 3.5%.
b. Effects of fat
During the extrusion process, fat can form complexes with proteins. These complexes can reduce the oxidation phenomenon of extruded products and prolong the shelf life of products. However, the free fat of extruded products will be rancid. The presence of fat affects the hydration of protein, making the material unevenly mixed and unable to form a stable extruded material. In practice, the fat content is controlled below 1%.
c. Other factors
The raw material has a great influence on the puffing technology, among which the fiber and fat have the greatest influence. When producing low-denatured soybean meal, attention should be paid to strengthening the control. At the same time, the raw material protein (dry basis) is required to be ≥50% and the nitrogen solubility index (NSI) ≥60% , Moisture≤8%, Ash content≤6%, particle size 80～120 mesh, pH value 7.0～8.5.
3.2 Influence of operation on puffing
a. The effect of moisture
Water is the basis for forming the microporous structure of the puffed product. For example, the material lacks water during the extrusion process in the body, the peptization effect of the protein is not good, the viscosity of the material is poor, and the puffed product has few pores, which affects the puffing degree; if the water is too large, The plastic viscosity of the material is too large, causing the extrusion pressure to be unstable, which can cause material spray from the extruder, and the product is poorly formed. Therefore, the moisture content of the extruded material is generally controlled at 23% to 30%.
b. Influence of temperature The temperature of the extruded material is closely related to the operating temperature of the extruder. Generally, the discharge temperature of the extruder is about 100°C. Under the condition of a certain amount of water in the extruded material, if the temperature of the extruded material is too low, the material will be brought into the extruder. The heat of the extruder is small, the sum of the heat generated by the material during extrusion and the heat brought into the body by the material itself is not enough to make the temperature in the extruder reach the required temperature condition, and the extruded material is not fully cooked, but is sandwiched. Puffed products are difficult to form a uniform texture and are loose and brittle. On the contrary, if the material enters the extruder and has not been extruded and matured, the gelling effect of the material is lost, and the material cannot form a uniform texture in the body. In addition, due to excess heat, it is easy to "burnt" the puffed material. Therefore, the temperature of the extruded material is generally controlled at 70 to 100 °C, and the maximum temperature of the extruder operation is less than 160 °C.
c. Influence of motor current
The operating current of the extruder reflects the intensity of the work load of the extruder. The operating current is small, the work load of the extruder is light, the pressure in the machine is small, and the extrusion and kneading effect cannot be achieved, and the extruded material is loose and brittle. Small pores and small puffing degree affect the functionality of the product and are not conducive to the safe operation of the equipment. In order to ensure a good extruding effect, the actual current of the extruder can be controlled by adjusting the amount of material, which is generally 70% to 85% of the rated current. In addition to the influence of the above factors, there are many situations in the actual operation, such as the temperature of the steam, the amount of feeding, the adjustment of the different operations of the required product types, etc., which should be strictly controlled during production.
3.3 The influence of equipment on the puffing effect
Equipment is the foundation of the process, and the condition of the equipment directly affects the puffing effect. The extruder is composed of main machine, auxiliary machine and control system. The failure of the main machine will directly cause production stoppage, while the failure of auxiliary machine and control system will affect the color, water absorption, oil absorption, puffing rate, molding status, etc. of the extruded product. Therefore, the production Make sure the equipment is in good condition.