1、Particle size

　　The grain size of soybean meal refers to the grain size with different structure in soybean meal. Although the grain size of soybean meal is not specified in the national standard, the grain size of soybean meal as a commodity has a certain influence on its trading price. It is generally required that the shape of soybean meal has loose granule or flake. Any meal that is too fine or too large will not be liked. The main factors that lead to the overbreaking and overfineness of soybean meal are as follows: low moisture of soybean; Small crushing size; Thin; Long time of steaming and frying in the steam extractor; Soybean meal is low in moisture. Caking of soybean meal is a common phenomenon in the primary leaching of soybean. The content of water, residual solution, residual oil and urease in caked soybean meal was much higher than that in normal meal, which would not only reduce the feeding value of soybean meal, but also make it inconvenient for feed manufacturers to store and process it. The main factors leading to the caking of soybean meal include: high water content of soybean; Immature and post-ripening soybeans used in oil production; The billet has high immersion water; Low leaching temperature; The quality of direct water vapor is poor; Insufficient steaming and drying time; The material is too high. In addition, soybean meal with high temperature and high water content tends to grow into large chunks during the period of bulk storage in the meal storehouse, and in severe cases, it will become moldy and become quality until it loses its feeding value.

　　2、Colour and lustre

　　Normal soybean meal should have the inherent yellowish-white to yellowish-brown color of soybean meal itself. When processing aging, red heat, mildew soybean, or steaming and baking time is too long, soybean meal color is darker until reddish brown. When there were more immature soybeans or green beans, the soybean meal was bluish green and had a poor appearance. When the quality of the direct water vapor is poor or the evaporation time is short, the soybean meal becomes white.

　　3、Smell

　　Normal soybean meal should have its own smell, no peculiar smell. When processing red heat, mildew soybean, soybean meal often have rancid smell; When residual solution and urease exceed the standard, soybean meal often has a heavy solvent taste and bean-fishy taste. In addition, some enterprises in order to achieve income, often hydration oil feet and waste drift soil mixed into soybean meal. The rancidity of the hydrated oil base will give the meal an unpleasant smell and the waste drift soil will aggravate the color of the meal. This method of generating income shall be prohibited.

　　4、Protein content and influencing factors

　　Protein content is an important index of soybean meal, which directly reflects feeding value of soybean meal.

　　40-50% soybean meal containing protein, lysine 2.5% ~ 3.0%, 0.6% ~ 0.7% of tryptophan, methionine 0.5% ~ 0.7%, and cystine 0.5% ~ 0.8%; Less carotene, only 0.2 ~ 0.4 mg/kg, amine, riboflavin 3 ~ 6 mg/kg each, niacin 15 ~ 30 mg/kg, choline 2200 ~ 2800 mg/kg. Methionine is deficient in soybean meal, crude fiber mainly comes from soybean skin, and nitrogen free extract mainly consists of disaccharide, triose and tetrose starch. The mineral content is low in calcium, low in phosphorus, low in vitamin A, vitamin B and vitamin B2.

　　The protein content of soybean meal is related to the following factors: first, the protein content of soybean raw materials; The second is the pretreatment technology of soybean. For example, the protein content of soybean meal produced by peeling technology was 7-8% higher than that of conventional technology. Third, water content and crude fat in meal also have certain influence on protein content.

　　5、Moisture content and influencing factors

　　Water content is another important index of soybean meal. When the water content in meal exceeds the allowable value, it will not only reduce the nutritional value but also be inconvenient for long-term storage. But the moisture is too low for the meal coke to burn easily. For the sake of economic benefit, most soybean meal produced in oil extraction plant is on the high side. The problem is especially acute in winter. The main factors affecting the water content of soybean meal include: the water content of bean preform, the working temperature of the extractor, the quality of direct water vapor, the structure of the steam extractor, the height of the dissolute layer and the transport mode of the meal, etc. If the direct water vapor with water, the working temperature of the extractor is low, the material layer of the desolvation layer is high, then the water content of the soybean meal is high.

　　6、Urease activity and its influencing factors

　　Raw soybean meal contains a variety of anti-nutritional factors, especially anti-trypsin inhibitor (TI), the activity of which is directly related to the digestion, absorption and utilization of soybean meal protein in monogastric animals. When pigs and poultry feed raw soybean meal, it will cause diarrhea, thus affecting weight gain and egg production rate. For calves and piglets, it may cause severe diarrhea, slow weight gain, or even death, while UA in soybean meal can also inhibit the digestion and absorption of nutrients in feed. Due to the positive correlation between TI content and UA content in soybean meal, the two were destroyed at the same rate under the conditions of high temperature, high humidity and high pressure, so urease activity was often used to represent the degree of destruction of anti-nutrition factors such as trypsin in soybean meal. The high urease activity indicated that the anti-nutrient factors in the meal were not effectively destroyed and the soybean meal was not matured. But the lower the urease activity, the better. The low urease activity indicated that soybean meal was overheated, and lysine, arginine and cystine in soybean meal would be destroyed due to overheated, and the Maillard reaction would further reduce the nutritional value of soybean meal.

　　(Maillard reaction, also known as "non-enzymatic Browning reaction", was proposed by French chemist L.C. Macillard in 1912. The so-called Maillard reaction is a kind of non-enzymatic Browning that widely exists in the food industry. It is a reaction between carbonyl compounds (reducing sugars) and amino compounds (amino acids and peptides). Through a complex process, the final formation of brown or even black macromolecular substances like melanin, also known as the carbonyl reaction.

　　It can be seen that reasonable control of urease activity in soybean crushing process is an important task in soybean immersion oil production.

　　The urease activity content is related to the following factors: first, the production process, such as pre-pressed - leach production process and expanded - leach production process, the urease content is less; The second is the time of desolution. Since the combined action of heat and humidity is an important condition for the passivation of urease, prolongation of evaporation time can reduce the content of urease in the meal. Thirdly, the softening, drying and steam quality of soybean have certain influence on urease activity.

　　Relationship between nutrition and urease activity of soybean meal

　　Soybean meal is the best source of plant protein. In soybean oil leaching and production,DTDC steam extractor has the following effects on degreasing meal :(1) removing solvent; (2) Destructive inhibition of antitrophic factors; (3) Control the degree of protein denaturation of soybean meal; (4) Adjust the water content of soybean meal; (5) Adjust the color and aroma of soybean meal. In order to detect the quality of soybean meal, the state and the enterprises have established the indexes of soybean meal. The moisture content of the meal was examined by drying weighing method or rapid moisture meter. The inactivation and maturation of antitrophic factors were determined by urease activity and sensory detection.

　　Antitrypsin is an inhibitor of protease in raw beans. It inactivates trypsin and rennet in the digestive tract, reduces the digestibility of protein, and causes the compensatory increase of pancreas. Trypsin is rich in thionine and secretes digestive enzymes in large quantities, which aggravates the deficiency of sulfur-containing amino acids in soybean protein. In addition, allergenic proteins such as soya globulin and 2 soya globulin are also important as they reduce feeding efficiency and increase diarrhea in young animals such as piglets. Soybean contains different amounts of urease, which is close to the content of antitrypsin. The degree of heat denaturation is similar to that of antitrypsin. Therefore, the appropriate urease activity detection range can be developed as an indirect estimation index of the suitability of soybean meal processing to supervise and guide the production. At the same time, there is a similar proportional relation between the urease activity of soybean meal and the degree of heat denaturation of soybean meal, that is, the urease activity of soybean meal is used to indicate the maturity degree of soybean meal.

　　Such as Thailand zhengda group concluded that soybean meal of urea enzyme activity in 0.05 0.25 (Δ pH); The feed industry association recommended index for 0.05 0.20 (Δ pH); My company based on market index for 0.05 0.30 (Δ pH). The domestic oil processing and feed enterprises all agree that urease activity is the mark to judge the maturity of soybean meal and use it to guide the production and purchase of soybean meal and feed.

　　7、Residual solvent and its influencing factors

　　It is stipulated in national standard that the residual solubility of soybean meal is no more than 700mg/kg. Feeding livestock and poultry with soybean meal with high residue will not benefit the growth and development of animals and may cause various diseases until death. The factors affecting the residual solubility of soybean meal are as follows: first, the quality of direct water vapor; Second, the evaporation time is reflected in the height of the material layer; Third, the structure of the steam extractor includes the diameter and number of steam jet holes; The fourth is the vapor phase temperature of the steam extractor. The residual solvents in the meal are closely related to the urease content. The urease activity of soybean meal with excess residue is often higher than that of soybean meal, so it is very important to control the residue amount of soybean meal.

　　8、Ash content and its influencing factors

　　Ash content in soybean meal is directly related to sand content and mud content in soybean. The high content of sand and mud will reduce the palatability of soybean meal. It is an important measure to reduce ash content of soybean meal to strengthen cleaning and air suction and dust removal of soybean.

　　9、What is protein solubility and why is it necessary to measure it?

　　High temperature enables reducing carbohydrates such as glucose to react with the EPSI1on free amino acid of lysine, known as the Mail1ard Reaction. As a result, lysine molecules become unusable, thus reducing the digestibility of proteins. Other amino acids in protein molecules, such as arginine, histidine, and tryptophan, are also affected by overheat. Reducing compounds also include ketones and aldehydes. The product of the Maillard reaction appears brown. So it's also called the brown reaction.

　　High temperature enables reducing carbohydrates such as glucose to react with the EPSI1on free amino acid of lysine, known as the Mail1ard Reaction. As a result, lysine molecules become unusable, thus reducing the digestibility of proteins. Other amino acids in protein molecules, such as arginine, histidine, and tryptophan, are also affected by overheat. Reducing compounds also include ketones and aldehydes. The product of the Maillard reaction appears brown. So it's also called the brown reaction.

　　The principle is that heating causes free amino acids to form intermolecular and intramolecular bonds with groups of other compounds that cannot be opened by digestive enzymes, thus reducing the solubility of proteins.

　　In the late 1960s, Purina Feed Company first used protein solubility as a method to evaluate the suitability of soybean meal processing.

　　Araba and Dale concluded in their 1990 paper that for chickens, soybean meal with a protein solubility below 70% was nutritively damaged, and soybean meal with a protein solubility below 65% was almost certainly overheated.