Introduction to soy protein concentrate

Soybean protein concentrate (SPC) is a product of further processing of soybeans. Compared with ordinary soybean meal, its crude protein content is about 30% higher. Since the industrial production of SPC in the 1950s, it has been widely used in the food and feed industry.

1. Definition
Soy protein concentrate (SPC) refers to using soybeans as raw materials and removing the oil and low-molecular soluble non-protein components in soybeans through processing techniques such as crushing, peeling, extraction, separation, washing, and drying. After separation (mainly soluble sugar, ash, gliadin and various odor substances, etc.), the prepared soy protein product contains more than 65% (dry basis) protein.

2. Processing process
After extraction, low-temperature desolvation of soybean meal is preferred. High-temperature leaching of the meal can also be used, but the yield is low and the quality is poor.
The current methods for producing concentrated protein include moist heat extraction, dilute acid extraction, alcohol washing, ultrafiltration and membrane separation.

1) Moist heat extraction method
The wet heat extraction method was eliminated due to the poor flavor, color and functional properties of the extracted soy protein concentrate.

2) Dilute acid precipitation method
Utilizing the principle that the soybean meal powder leaching liquid has the lowest protein solubility at the isoelectric point (pH 4.3-4.5) state, the insoluble proteins and polysaccharides are separated from the soluble carbohydrates and low-molecular proteins by centrifugation, and then neutralized, concentrated, and dried and dehydrated. Concentrated protein powder is obtained.
This method can remove the fishy smell of soybeans at the same time. The dilute acid precipitation method produces concentrated protein powder. The protein has good water solubility (high PDI value), but it consumes a lot of acid and alkali, has a low protein yield, and has poor overall benefits.

3) Alcohol washing method
Using the principle that soluble protein has the lowest solubility when the alcohol concentration is 60% to 65%, the alcohol solution is mixed with the low-temperature desolubilized meal to wash the soluble sugars, ash and alcohol-soluble proteins in the meal. The alcohol solution is then separated by filtration, and alcohol and sugar are recovered. The slurry is dried to obtain concentrated protein powder. The protein powder produced by this method has better color and flavor, and less protein loss.

4) Ultrafiltration method
Ultrafiltration is a new method that has just begun to be explored. The soybean protein concentrate produced by it has good functional properties and a high protein yield, but the product cannot be dried.

5) Membrane separation method
The membrane separation method uses an ultrafiltration membrane to remove sugar to obtain concentrated protein, and a reverse osmosis membrane to dehydrate and recover water-soluble low-molecular proteins and sugars. No wastewater treatment engineering is required during production, and the product has a high nitrogen solubility index (NS).

3. Physical and chemical properties
1) Quality indicators
Color: milky white, light yellow
Odor: The inherent odor of concentrated protein, no other odor.
Protein content (N*6.25): ≥65%
Moisture: 7-9%
Fat: <1%
Ash content: <6.0%
Total fiber content specified: <4%
NSI: 5-10%
Particle size: 100 mesh (90% passed)

2) The amino acid composition is greatly improved
SPC is a product of further processing of soybean meal. Compared with peeled soybean meal, the crude protein has increased by approximately 35.7%, and the amino acid content has also increased in varying proportions.

3) Anti-nutritional factors are significantly reduced
In addition to “concentrating” protein, SPC also significantly reduces soybean anti-nutritional factors. Soybean anti-nutritional factors mainly include two categories: the first category is antigenic proteins, such as protease inhibitors, soybean lectin, glycinin and β-glycinin, etc.; the second category is oligosaccharides such as sucrose, stachyose, Marshmallow etc.
The ways to remove anti-nutritional factors in SPC processing are:
①Solvents can remove most oligosaccharides;
②Solvents can denature proteins and destroy the soy antigen protein structure;
③Later heating temperature and time control can reduce heat-labile antigens, such as proteases Inhibitors, soy lectins and saponins, which cause flatulence, are also absent. The flavor of soy protein concentrate is improved due to the removal of soluble carbohydrates.

4. Application
1) Food
SPC can be used in the production of milk replacer powder, protein cast foods, minced meat, latex minced meat, meat rolls, seasonings, baked goods, baby food, simulated meat, etc. The selection should be based on the functional properties of different concentrated proteins.

2) Feed
SPC is a plant-based protein with a relatively complete amino acid composition and is a good source of animal protein feed. In a study of the energy, amino acid and phosphorus digestibility of soybean protein concentrate and soybean meal in growing pig diets, researchers found that SPC has higher digestibility and metabolizable energy than soybean meal, but SPC has higher standards for most amino acids than soybean meal. There is no difference in ileal digestibility and standard total intestinal phosphorus digestibility, and it can be used as a high-quality feed.
In addition, due to its low price, SPC can also be used as a substitute for some fishmeal in aquaculture diets, but the proportion of SPC in the feed should not exceed 20%.