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Natural toxic substances in soybeans

July 30, 2021

1.Trypsin inhibitor

Soybeans contain a toxic substance called trypsin inhibitor (TI). Trypsin inhibitor is not a single protein, but a mixture of various proteins. Its number is 4-7. It has the effect of inhibiting the activity of trypsin in the small intestine, so it will hinder the digestion, absorption and utilization of protein in food after consumption. , Its toxicity can cause pancreatico-intestinal hypertrophy. When heated under moist heat conditions, trypsin inhibitor is easily destroyed. At 80°C, its residual viability is still more than 80%, but when the heating temperature is 100°C and the heating time is 10 minutes, the activity unit of trypsin inhibitor is 13; When the heating temperature is 120°C and the heating time is 10 minutes, the activity unit of trypsin inhibitor is only 3. Therefore, in industrial production, suitable heating temperature and heating time can be determined according to different needs, so that the activity of trypsin inhibitor can be reduced to the level required for production.


2. Lectin

Phytohemagglutinin is a substance in plants that can agglutinate red blood cells in animal blood. There are at least four proteins with this function in soybeans, which can cause red blood cell aggregation in rabbits and mice. However, its activity can be lost through digestion, proteolytic enzymes or damp heat in the human body, even if part of the residue enters the intestinal wall, it will not be absorbed. It is also the same as trypsin inhibitor, which is easily destroyed by heating under humid and hot conditions. Therefore, if the soybean food is heated during the production process, hemagglutinin will not cause adverse effects on the human body.

3. Flatulence factor

Since soybeans contain raffinose and stachyose, they cause flatulence when fermented. Alpha-galactosidase is not produced in the human digestive tract, so these sugars cannot be digested and absorbed by the human intestines and stomach. When they reach the lower intestinal tract, they manifest as nausea, diarrhea, stomach gurgling, and flatulence. It is generally explained that the above-mentioned oligosaccharides can be used with fungal enzymes, but the actual effect is not obvious. Some scholars have put forward another point of view, that is, the above-mentioned oligosaccharides may not be the only cause of flatulence. What is interesting is that tofu does not produce flatulence, even if it has flatulence, it is very weak. Recent studies have shown that the oligosaccharides in soybeans are not only harmful factors, but also bifidobacteria proliferation factors.

4. Substances that cause thyroid swelling
Soybean contains thyroid swelling factor (GTG), and heat treatment alone is not enough to inactivate GTG in it. It is generally believed that it does not affect the growth of the human body, but can cause thyroid hypertrophy, because the GTG in soybeans may be preferentially combined with iodine in food in the animal body to reduce the iodine required by the thyroid gland, thereby causing iodine-deficiency goiter. If iodide is added, the effect can be eliminated, and heating can also disappear partly.
5. How to eliminate natural toxic substances
The natural toxic substances in soybeans can be divided into two types: thermally stable and thermally unstable according to the degree of heat resistance. Trypsin inhibitor, lectin, thyroid swelling factor, etc. are all thermally unstable and can be eliminated by heat treatment; cottonseed Sugar, stachyose, saponins, plant hormones, etc. are stable to heat and can only be removed by washing and alcohol solution treatment during the production of soybean products. The traditional processing methods of soy products unconsciously eliminate the influence of anti-nutritional factors. With the continuous emergence of new soybean foods, corresponding measures should be taken to remove the natural toxic substances in soybeans to ensure the nutritional value and edible safety of soybean foods. At present, there are mainly the following methods to remove these harmful substances:
(1) Far-infrared heating treatment: Because far-infrared rays have strong penetrating power, the use of far-infrared heating to treat soybeans can inactivate thermally unstable natural toxic substances in a short period of time, saving energy and time.
(2) Moisture heat treatment: soak the soybeans for 4 hours, steam them with atmospheric steam for 30 minutes, and then dry them with hot air; or boil the soybean milk for 5-10 minutes, or steam the soybean flour with 98kPa steam pressure for 20 minutes, etc. It can be used in different beans. Used in product processing technology.
(3) Heat treatment: Because most of the natural toxic substances in soybeans are active proteins with different molecular weights, effective heat treatment can basically inactivate or inactivate their activity. Soybeans were heated in boiling water for 1 min, 3 min, and 9 min. The inactivation rates of TI were 62.14%, 94.15%, and 96.11% respectively. The TI was basically inactivated after 20 minutes of boiling. While under normal pressure, 100 ℃ steam heating treatment of soybean meal that has not been soaked in water for 15 minutes, the TI inactivation rate is only 90-92%. In addition, although heat treatment can remove natural toxic substances in soybeans, overheating tends to cause severe denaturation of protein and loss of certain amino acids, resulting in a decrease in the digestibility of soybean products and their nutritional value. Therefore, in the heat treatment process, the appropriate heating method, effective heating temperature, heating time and moisture should be selected according to the characteristics of these harmful substances in order to obtain a more ideal result.
(4) Adding additives: In the soybean food production process, appropriate amount of corresponding additives can be added to antagonize or inhibit the toxicity of certain natural toxic substances in soybeans. Adding iodide to soy products can prevent goiter caused by GTG; adding more than normal vitamin D3, vitamin E and vitamin B2 to chicken feed containing soybean meal can prevent chicken rickets and other vitamins Deficiency; Soybeans are soaked in 0.15% NaHCO3 aqueous solution at 50℃ for 4-6h, which can also eliminate the harm of TI, GTG and other harmful substances. From this point of view, this type of method is relatively effective in removing soybean anti-nutritional factors, and has basically no effect on the nutritional value and quality of soybean protein, and is simple to operate and easy to promote and apply.
(5) Enzymatic hydrolysis: In recent years, people have also discovered that the use of certain microbial proteases and enzymatic hydrolysis under specific conditions can also decompose and destroy the structure of certain natural toxic substances in soybeans. This kind of method not only overcomes the defect of reducing the PER of soy protein caused by excessive heating, but also increases the solubility of soy protein, and improves the bioavailability and nutritional value of soy protein products. However, research reports on this aspect are still relatively rare.
In summary, soybeans contain a variety of natural toxic substances. In the production of soybean food, if effective measures are not taken to remove them, long-term consumption of such soybean products will inevitably produce certain adverse reactions or endanger human health.