Summary of research progress on anti-nutritional factors

introduction

The widespread presence of anti-nutritional factors in feed not only reduces animal performance, affects the nutrient digestibility of feed, but also causes damage to the health of the gastrointestinal tract and even harms the immune system. Therefore, how to study it in depth, eliminate the negative effects of anti-nutritional factors and improve the utilization efficiency in actual production is a major issue facing nutritionists. So far, people have been using the research methods of nutrition, microbiology, histology and biochemistry to explain the possible mechanism of anti-nutritional effects, and made some progress. At the same time, scientists have also conducted a lot of research on the inactivation of nutrient factors, including physical, chemical, biological and genetic breeding. The process parameters are also gradually improved, and achieved in production practice. good effect. However, there are still many scientific issues that need to be explored.

1 Types and distribution of anti-nutritional factors

According to Huisman's 1992 classification method, the anti-nutritional factors in the feed were divided into six categories, (1) adversely affecting the digestion and utilization of the protein. Such as trypsin and chymotrypsin inhibitors, plant lectins, phenolic compounds, saponified compounds and the like. (2) has an adverse effect on the digestion of carbohydrates. Such as amylase inhibitors, phenolic compounds, bloating factors and so on. (3) It has an adverse effect on the utilization of mineral elements. Such as phytic acid, oxalic acid, gossypol, glucosinolates and so on. (4) Vitamin antagonists or anti-nutritional factors that cause an increase in vitamin requirements in animals. Such as dicoumarin, thiamine enzymes and the like. (5) Anti-nutritional factors that stimulate the immune system. Such as antigenic proteins and the like. (6) Comprehensive anti-nutritional factors, which have an impact on the utilization of various nutrients. Such as water-soluble non-starch polysaccharides, tannins and the like. Anti-nutritional factors are widely found in the roots, stems, leaves and fruits of plants.

2 Hazards of anti-nutritional factors

Anti-nutritional factors affect the digestive enzyme activity in the body, the tight binding with the digested substrate, the competitive inhibition of nutrient absorption, and the formation of a special physical structure that affects the hydrolysis of the substrate by digestive enzymes and directly stimulates the immune system. It interferes with the absorption of nutrients by livestock and poultry, further affecting the growth rate and health of animals.

2.1 Protease inhibitors

Protease inhibitors of great importance in animal nutrition are KTI and BBI. KTI and BBI combine with protease to form a stable compound, which inhibits the activity of the enzyme and affects the hydrolysis of the feed protein. At the same time, it causes the endocrine cells of the pancreatic mucosa to release more CCK-PZ hormones, which cause the pancreas to produce more digestive enzymes (such as trypsin, amylase, etc.), which increases the pancreas compensation of animals, especially Small animals are obvious. KTI significantly affects animal growth due to reduced feed intake and affects nitrogen digestion, absorption and deposition. In addition, it also causes an increase in the rate of gallbladder emptying, reducing fat absorption. Unlike KTI, BBI inhibitors do not significantly affect feed intake, feed conversion, and weight gain, but BBI also causes massive pancreatic secretion and pancreatic hypertrophy.

2.2 Plant lectins

The plant lectin mainly affects the epithelial cells of the small intestine, thereby affecting the absorption of nutrients, causing changes in digestive enzyme activity, loss of secretion of endogenous proteins, and increase in the amount of mucin. In addition, toxic lectins enter the circulatory system, causing the production of specific IgG lectin antibodies. In short, these result in reduced nutrient digestibility, reduced nitrogen deposition, and sometimes small intestinal villi due to the binding of its specific oligosaccharides to the cell surface. Eventually it leads to diarrhea, which leads to a decrease in animal body weight gain and a decrease in feed efficiency. It inhibits the growth of the thymus and causes hypertrophy of the liver, pancreas and small intestine. When a large amount of lectin is ingested, the animal's body weight can be rapidly decreased and poisoned. In addition, it also changes the ecological environment of intestinal microbes. It also has an antagonistic effect on IgA produced in the intestine and has a destructive effect on the immune system.

2.3 Phytic acid

Phytic acid is a strong chelating agent, which can sequester various mineral elements such as Zn2+, Ca2+, Mn2+ and Fe2+ to form a poorly soluble phytic acid-metal complex, which affects the absorption and utilization of these mineral elements. Its biological potency is significantly reduced. In the pH medium below the isoelectric point of the protein, the phytic acid-metal ion-protein ternary complex is easily formed, so that the solubility of the protein is greatly reduced and the absorption and utilization of the protein by the animal is also affected. In addition, the utilization of phosphorus is reduced. Because of the lack of phytase hydrolyzing phytate phosphorus in chickens, pigs and other monogastric animals, the utilization rate of phytate phosphorus is reduced, resulting in a large amount of phosphorus not being digested and utilized, resulting in soil, Phosphorus pollution from water sources.

2.4 Tannin

Tannins bind to proteins and precipitate proteins. Tannin has a higher affinity for proline-rich proteins. In addition, tannins can also be combined with metal ions. Tannins also inhibit the activity of the enzyme. Therefore, tannins affect the digestion and utilization of nutrients. In addition, the bitter taste of tannin, when it enters the digestive tract, can decompose to produce a strong stimulating gallic acid, affecting palatability and feed intake. Tannins may also damage the intestinal mucosa and corrode the intestinal wall.

2.5 Gossypol

Free gossypol is a cellular vascular neurotoxin. Its active carboxyl and hydroxyl groups can bind to proteins, reducing protein utilization. In addition, free gossypol has a stimulating effect on the gastrointestinal mucosa, causing inflammation of the gastrointestinal surface, bleeding, and can increase the permeability of the blood vessel wall, so that plasma, blood cells infiltrate into the peripheral tissue, causing plasma infiltration of the damaged tissue.

2.6 Oligosaccharides

After the oligosaccharide enters the digestive tract, it is fermented by microorganisms, producing a large amount of CO2, H2 and a small amount of CH4, which causes intestinal flatulence, leading to abdominal pain, diarrhea, etc., affecting the absorption and utilization of nutrients, and reducing the energy value of the diet.

2.7 antigenic proteins (Glycinin and -Conglycinin)

The antigenic proteins Glycinin and b-Conglycinin in soybean can stimulate the intestinal immune system of young animals and stimulate allergic reactions, resulting in decreased animal performance, intestinal mucosal damage, diarrhea and other adverse symptoms.

2.8 Other anti-nutritional factors

3 passivation of anti-nutritional factors

Anti-nutritional factors passivation methods and many, including physical, chemical, biological, genetic improvement and the addition of other nutrient active ingredients to reduce the harm of anti-nutritional factors, so that the animal's production performance is improved. Physical methods mainly include heat treatment, mechanical processing and water immersion. The heat treatment method is mainly directed to heat-labile anti-nutritional factors such as trypsin inhibitor and lectin. The heat treatment method includes a dry heat method (baking, microwave irradiation, infrared radiation, etc.) and a moist heat method (cooking, hot pressing, extrusion, etc.). The mechanical processing is mainly applied to the anti-nutritional factors with high seed coat content, and the seed coat can be separated by mechanical processing to eliminate the anti-nutritional factors. The water immersion method is suitable for anti-nutritional factors dissolved in water, such as tannin.

Chemical passivation achieves the purpose of passivation by adding a chemical substance to the feed and reacting under certain conditions to deactivate or reduce the activity of the anti-nutritional factor. Adding the proper amount of methionine or choline as a methyl donor in the feed can methylate the tannin to achieve the purpose of inactivating tannin. In addition, the addition of a certain amount of sodium sulfite can break the disulfide bond of trypsin inhibitor, thereby reducing its activity; using copper sulfate as a chemical detoxification agent for rapeseed cake, and ferrous sulfate as a passivating agent for gossypol. However, chemical methods tend to cause residues of chemical agents and a decrease in the nutritional value of the feed.

The bio-passivation method mainly aims to eliminate anti-nutritional factors by biological fermentation and addition of active nutrients or enzyme preparations. The combination of divalent iron ions and free gossypol forms a gossypol-iron complex that is difficult to absorb in the digestive tract, making it inactive; divalent iron ions can also reduce the accumulation of gossypol in the liver, thereby preventing accumulation of poisoning. effect. The ferrous iron, copper and zinc ions can form insoluble complexes with isothiocyanates and oxazolidine thiones, and are not detoxified by absorption by livestock and poultry. The addition of phytase can not only degrade phytate phosphorus in various plant feeds such as bran, but also increase the utilization of phosphorus and reduce the pollution of fecal phosphorus to the environment; and it can also chelate calcium and zinc by phytic acid. Copper, iron and protein are also released, restoring the activity of inhibited amylases, lipases and proteases, and improving the digestion and absorption of various nutrients.

4 Detection of various anti-nutritional factors

Traditional methods for detecting anti-nutritional factors include enzymatic chemistry, ultraviolet spectrophotometry, and the like. With the development of cloning antibody technology, enzyme-linked immunosorbent assays for anti-nutritional factors such as lectin, trypsin inhibitor, and soybean antigen protein have been gradually established and are officially sensitive and accurate. The continuous improvement of high-efficiency chromatography technology has also applied this high-tech technology to the detection of anti-nutritional factors such as oligosaccharides and isoflavones.