Abstract Trivalent chromium ions are an important component of glucose tolerance factor, which can enhance the action of insulin and is one of the indispensable trace elements in humans and animals. Organic chromium compounds have a variety of extremely important active functions in living organisms. If the body is deficient in chromium, it will lead to diabetes and other related diseases. The lack of chromium in animals will lead to stress sensitivity, suppression of immune function, decline in reproductive function, and carcass. Quality declines, etc. In this paper, the biological functions of organic chromium compounds and their synthesis methods are reviewed. The methods of product detection and quality evaluation are introduced, and their development prospects are prospected.
Keywords feed additive; organic chromium; biological function; synthesis; quality evaluation CLC number S816.72
Schwarz and Mertz found a new nutrient, Glucose Tolerance Factor (GTF), in beer yeast, and later identified GTF as a trivalent containing niacin, glycine, glutamic acid, and cysteine. Organic chromium complex. As an active form of chromium, GTF has an effect of enhancing insulin activity. In intensive feeding of poultry, animal nutrition stress, environmental stress, immune stress and metabolic stress can lead to a series of changes in animal glucose metabolism and mineral metabolism, causing glycogen degradation and gluconeogenesis, glucose The use of reinforcement leads to an increase in chromium mobilization and eventual excretion. Animals that lack chromium can produce metabolic disorders of glucose, lipids, and proteins. The addition of chromium to stressed animals increases immunity, improves endocrine, reduces morbidity and improves performance.
Chromium salts are generally classified into trivalent chromium salts and hexavalent chromium salts, as well as organic chromium salts and inorganic chromium salts. Hexavalent chromium is more toxic and trivalent chromium is less toxic, but it is not allowed to add inorganic chromium to livestock feed under the current conditions of the feed law. The trivalent chromium salt of picolinic acid is non-toxic and can be used for the addition of feed. Among the trivalent chromium salts of picolinic acid, the trivalent chromium salt of 2-picolinic acid (commonly known as organic chromium) is the most commonly used feed additive. At present, organic chromium as a feed anti-stress additive is mainly composed of similar complexes of GTF, such as chromium nicotinate, yeast chromium, chromium picolinate, amino acid chelate chromium and protein chromium. The absorption rate of inorganic chromium is very low, about 0.4% to 3% or lower (Yang Feng, 1991). Hexavalent chromium is easier to absorb than trivalent chromium, generally 3 to 5 times higher (Zhang Qiao, 1994); organic chromium The absorption rate is relatively high, for example, the absorption rate of chromium-glucose tolerance factor (GTF) in beer yeast by livestock and poultry is as high as 10% to 25%.
Beta-stimulant has been used in the pig industry in China. It can make the pig's buttocks muscles full and full, the thickness of the back fat is reduced, and the lean meat rate is increased. However, after the addition of β-agonists, leg muscles are soft, muscle tremors, heartbeats are accelerated, transport stress is not tolerated, and even some pale, soft, water-permeable pork or dry, hard black pork appears after slaughter. Since β-stimulants remain in pork, people may experience different degrees of poisoning after eating. Symptoms include palpitations, muscle tremors, dizziness, vomiting, and sweating. In view of this situation, many Western countries have banned the use of beta-agonists in animal production, and now the Ministry of Agriculture has also banned use. Organic chromium is an ideal substitute for beta-agonists. [next]
The main physiological role of chromium is to affect the metabolism of carbohydrates, lipids and proteins by strengthening insulin function. Recent studies have shown that in the high-intensity growth period of animals, chromium not only regulates protein metabolism, but also acts as an immunomodulator to affect animal health and growth performance. Chromium activates certain enzymes and appears to be involved in protein synthesis, nucleic acid and lipid metabolism. Chromium can reduce the incidence of animals and the amount of antibiotics used. Adding trivalent chromium to chick diets can improve growth performance and feed efficiency. If supplementation of chromium to pigs can increase or enhance energy metabolism, improve carcass traits, increase growth rate, and also reduce serum cholesterol and cortisol levels, and increase immunoglobulin concentration. If chromium is deficient, animals generally cause poor growth, shortened life, disordered metabolism of glucose, lipids and proteins, and decreased quality of animal products. In China's food structure, chromium is ingested very little due to refining, processing and soil leaching. Therefore, both humans and animals are deficient in chromium. This effect can be easily seen from the favorable reaction of animal production after chrome supplementation. It can be said that the amount of chromium in the diet used in livestock production is insufficient. The supply of chromium should be Mention the agenda. If there is not enough GTF, the effect of insulin will be inhibited. With the help of GTF, insulin can rapidly transport glucose and important amino acids, through the cell membrane, into cells, produce energy and form tissue. The blood sugar concentration is thus maintained at a normal level, and amino acids are used for protein synthesis to produce muscle. In addition to participating in the metabolism of proteins and carbohydrates, chromium plays an important role in the metabolism of lipids. It appears to be a regulator of serum cholesterol levels in animals, thereby preventing the accumulation of adipose tissue. It can increase the activity of insulin, participate in protein synthesis and metabolism of nucleic acids and fats, reduce body fat content, and increase lean meat rate. Chromium can also strengthen the immune system in animals, improve the body's resistance to adverse conditions and stress conditions, increase lean meat ratio, reduce fat, improve anti-stress ability and immunity. Improve feed returns and promote animal growth. Increase the sow rate and reduce the mortality rate of suckling pigs. In recent years, along with the progress of chromium in livestock and poultry biology research, it has been found that chromium (III) has a strong advantage in reducing livestock stress, promoting growth, improving ketone body quality, enhancing immunity and improving reproductive performance. , chromium has great development potential and application prospects in the future breeding production practice. Chromium (III) as a feed additive can promote the weight gain of growing and finishing pigs, increase feed intake and shorten the feeding cycle.
1 Biological functions of chromium 1.1 Improving carcass quality Studies have shown that chromium supplementation reduces circulating cholesterol levels in blood of test animals and livestock fed with chromium-deficient diets. Cholesterol is a precursor of synthetic cortisol, so supplementation with chromium can improve Meaty. Chromium supplementation in fattening pig diets improves carcass quality and lean meat rate, and reduces backfat thickness and fat percentage. The reason why chromium improves carcass quality is currently believed to be that chromium enhances the effective utilization of glucose by peripheral tissues, reduces protein degradation, and increases the concentration of growth hormone. Many experiments have shown that chromium supplementation during the growing season has no effect on weight gain and feed efficiency, and can increase daily gain during the fattening period. Harper (1995) used weaned pigs as the test object and added 200μg/kg organic chromium to the basic diet of corn-soybean-whey powder. As a result, the piglet performance improved, and the backfat thickness decreased significantly during the finishing period (P<0.01). . Page et al. (1992) supplemented 200 μg/kg of chromium picolinate in the feed of growing and finishing pigs, which also significantly improved carcass quality and lean meat rate, and reduced the thickness of the 10th ribbed back. Lindemann et al. (1995) confirmed that when pigs were added with 200 μg/kg of organic chromium at a weight of 14.5 to 104.3 kg, the longest muscle area of ​​the back was increased by 2.0 cm 2 , the thickness of the back ridge of the 10th rib was reduced by 3.4 mm, and the lean meat rate was increased by 2.1%. In addition, many scholars have studied the effects of different sources of chromium and different feeding cycles on the quality of growing and finishing pigs, and the results confirmed the effect of chromium. Other livestock, such as chicken, duck, cattle, sheep and other animals have proved that chromium can significantly improve carcass quality.
1.2 Promoting growth The use of chromium can increase the weight gain of livestock and poultry, increase feed intake and shorten the feeding cycle. Lindemann et al. (1995) tested not only the effect of chromium on carcass traits, but also the changes in pig growth performance when testing pigs aged 14.5-104.3 kg. The results showed that 200, 500, and 1 000 μg were added to the feed. In the case of organic chromium in kg/kg, the daily gain in the 200 and 500 μg/kg groups increased from 0.83 kg to 0.84 and 0.86 kg, respectively, and the daily gain in the 1 000 μg/kg group did not change. The daily feed intake at 200 and 500 μg/kg increased from 2.43 kg to 2.48 and 2.55 kg, respectively, and there was no change in daily feed intake in the 1000 μg/kg group. The effect of adding dose at 500μg/kg was the most significant, but considering the effect on carcass traits, the authors thought that adding 200μg/kg was the most ideal. Some people also added and did not add two groups in finishing pigs to study the effect of chromium on daily gain. The results showed that in the 60-90kg stage and the 60-110kg stage, the daily weight gain of the added group was increased by 22.7% and 15%, respectively, compared with the non-added group, which proved that the addition of organic chromium is conducive to promoting growth. Many other scholars (Shbiyatno et al., 1993; Wang et al., 1995; Boleman et al., 1995) also reached similar conclusions. [next]
1.3 Improve reproductive performance Chromium can improve the reproductive performance of sows, significantly improve fertility, and add chromium-containing organic compounds to pig diets to increase the number of litters in sows.
The results of Lindemann et al. (1994) show that chromium-containing organic compounds can significantly increase the litter size of primiparous sows. A large number of results show that the application of organic chromium has improved many indicators of reproductive performance of livestock and poultry, and the fecundity has been significantly improved. Lindemann et al. (1994) showed that chromium picolinate can significantly increase litter size in primiparous sows. Yan Guiyu (1992) research on rabbits showed that chromium deficiency increased sperm deformity rate, decreased semen quality and the number of live births of female rabbits. Lindemann et al. (1995) also studied the effects of organochromium on breeding sows and their offspring, and the results reaffirmed the benefits of organic chromium in improving reproductive performance.
1.4 Enhancing immunity Chromium enhances immunity, first reported by the University of Guelph in Canada. Later, many scholars have done a lot of research in this field, mainly focusing on the study of cattle (Chang et al., 1992; Sartin et al., 1988; Bunting et al., 1994). Burton et al. (1993) added chromium to small beef cattle, which significantly increased the potency of the infectious bovine rhinotracheitis vaccine. In the same year, he experimented with lactating cows and found that chromium supplementation also increased many antigen-antibody reactions. Chang et al. (1992) also confirmed that chromium supplementation can increase the level of immunoglobulin in bovine serum. It is clear that chromium acts as an immunoregulatory factor in certain specific immune responses, and it enhances the body's disease resistance and adaptability by regulating the immune response.
1.5 Strengthening anti-stress effect It has been found that the addition of organic chromium is extensive. In addition to improving carcass quality and reproductive performance, promoting growth and enhancing immunity, it also shows improvement in endocrine and stress reduction. With the emergence of intensive farming, various factors (such as heat, transportation, hunger, congestion, pathogen attacks, etc.) can cause stress. Some people (Orr et al., 1990; Nockels et al., 1990) have shown that when cattle are stressed due to transportation, fasting, etc., the excretion of chromium in the urine increases, and there are similar phenomena in humans and rats (Borel et al., 1984; Anderson et al., 1988), show an increase in the demand for chromium under stress conditions. Chang et al. (1994) supplemented chromium in the diet of stressed cattle and found that the proliferative effect of peripheral lymphocytes of cattle was enhanced, indicating that the anti-stress effect was enhanced.
2 Synthesis of organic chromium
Organic chromium is an important class of feed and food additives developed in recent years, especially in the feed industry. According to the data, for an adult, the daily intake of chromium is at least 50μg, and for animals, the daily intake of organic chromium is 1μg/kg. It can be seen that the amount of organic chromium is very large. Organic chromium can significantly promote the growth of animals, which can greatly increase the lean rate of animals and the egg production rate of chickens and ducks. The product is non-toxic and harmless, and the production process is basically free of three wastes, which meets environmental protection requirements. There are many synthetic processes for this product, but according to the latest information, the main raw material for the production of organic chromium is 2-methylpyridine. The product is obtained by two-step reaction: firstly, 2-methylpyridine is obtained by oxidation. The product is obtained by reacting picolinic acid followed by 2-picolinic acid with a chromium salt.
2.1 Synthesis of chromium nicotinate 124 g (1 mol) of nicotinic acid was weighed into a 1 000 ml beaker, wetted with 100 ml of water, adjusted to a pH of about 8.0 with 6 mol/l NaOH, and heated to 80 °C. Also weigh CrCl 3 •6H 2 O 88g (0.33mol) in a 500ml beaker, add 300ml of water, heat to dissolve and heat to about 80 ° C, pour into the above sodium nicotinate solution with stirring, wash the beaker with a small amount of water The mixture was combined into the above reaction solution, and the pH was adjusted to 6.8 to 7.2 with 6 mol/l NaOH under stirring, water was added to a total volume of 900 ml, and the mixture was cooled to room temperature. After suction filtration, the filter cake was washed with water, washed once with ethanol (95%), filtered, dried, evaporated to dryness at room temperature, and then dried thoroughly at 110 ° C to obtain 140 g of gray nicotinate (III). [next]
2.2 Synthesis of 2-pyridine picolinic acid chromium 2-chromic picolinate, which is chromium picolinate or chromium picolinate. Li Xinsheng et al. added 4.3 g (35 mmol) of 2-picolinic acid in ethanol (dissolved in 20 ml of absolute ethanol) and 2.0 g (35 mmol) of potassium hydroxide in a 100 ml flask, stirred with heating for 10 min, and then added dropwise 2.6 g (10 mmol). An ethanol solution of chromium trichloride (dissolved in 30 ml of absolute ethanol) was stirred and refluxed for 1 h, and a precipitate formed. Filtration and vacuum drying gave 3.7 g of rose red powder, yield 90.2%, melting point &gt; 300 °C. A chromium 3-picolinate (ink green powder) and a chromium 4-picolinate (grey blue powder) complex can also be obtained in a similar manner. Zhou Baoxue et al [5] improved the synthesis method, using 2.66g CrCl 3 •6H 2 O and 3.69g pyridine acid, dissolved in 100ml water, mixed in 250ml flask, heated and stirred at 80 °C for 30min, the solution turned from green to red, Slowly adjust the pH of the solution to 6.0 with concentrated NH3•H 2 O, continue stirring for 1 h, and cool at 5 ° C in the refrigerator overnight to obtain a dark red product Cr(C 6 H 4 NO 2 ) 3 •H 2 O, suction filtration, repeated with water. It was washed, dried under vacuum at 55 ° C for 4 d, and the yield was 96%.
First Wen-yi 2-methylpyridine and the like using as a raw material, oxidized and complexed Synthesis of 2 successive reactions chromium picolinate, the optimal reaction conditions: 2-picoline and potassium permanganate, and chromium trichloride The optimum molar ratio is 1:2.5:0.35, the solvent amount is 22 times of 2-methylpyridine, the oxidation temperature is 80-82 ° C, the complexation temperature is 40-45 ° C, and the yield is 82.7%, which not only makes the synthesis process Simplified and reduced production costs.
2.3 Synthesis of methionine chromium Weigh DL-methionine 150g (1mol) in a 2 000ml beaker, weigh CrCl 3 •6H 2 O 88g (0.33mol) mixed with methionine, add 750ml water, stir and heat to about 80 °C. The pH of the solution was adjusted to 6.8 to 7.2 with 6 mol/l NaOH under stirring, and the reaction liquid changed from green to rose red. After cooling to 20 ° C or less, the filter cake was washed with water, dried, washed with 95% ethanol, and then dried, dried at room temperature, and then thoroughly dried at 100 ° C to obtain 152 g of rose red methionine chromium (III). The optimum reaction conditions were a pH of 7.0, a temperature of 80 ° C, a ligand molar ratio of Met:Cr=3:1, and a methionine concentration of 15%. The yield of methionine chelated chromium in this preparation was 48.41%. The molecular formula of chromium methionine is CrC 15 H 3 0N 3 O 6 S 3 , the structural formula is Cr(NH 2 CHCH 2 CH 2 SCH 3 COO) 3 , the relative molecular mass is 497.0. The solubility at 37 ° C is 42 mg/100 ml, and the melting point is 352. ~ 356 ° C.
3 Quality evaluation of organic chromium products Organic chromium is a compound composed of trivalent chromium ions and organic ligands. Due to different production methods, the quality of commercially available products is uneven, resulting in inconsistent content of trivalent chromium ions and organic ligands. That is, the purity or content of the product is not high, and the quality of the product is not good. Since the production of organic chromium products is generally carried out in the production process by adjusting the pH value, it is inevitable that some trivalent chromium ions will form chromium hydroxide precipitates due to the operation process and the conditions, so that the chromium content in the product is high. For example, the theoretical content of anhydrous chromium picolinate and chromium nicotinate chromium is 12.43%, while the content of chromium in commercially available products is generally above 14%, and some are higher. [next]
3.1 Determination and quality evaluation of chromium in organic chromium products From the analysis of material structure, the analysis of organic chromium can be carried out through inorganic and organic analysis. Inorganic analysis can directly detect the chromium element, but the disadvantage is that it is impossible to distinguish between the trivalent chromium necessary for the human body or the hexavalent chromium which is harmful to the human body, and it is impossible to know which group is connected with the chromium. Organic analysis can analyze the entire organic chromium molecule reasonably and accurately by the characteristic response wavelength, so it is an ideal test method. The method for determining the content of organic chromium is to use a high-performance liquid chromatography method to inject a standard solution and a sample solution into the chromatograph to characterize the retention time, and to compare the peak height or peak area of ​​the sample with the standard. However, this method requires a standard sample of the organic chromium, which is difficult to purchase.
Wan Yuping et al. Determination of chromium picolinate in health foods by high performance liquid chromatography. Chromatographic conditions: Agilent C18 column (5 μm, 4.6 mm × 150 mm), mobile phase methanol: acetonitrile: 0.1 mol/l NaH 2 PO 4 (H 3 PO 4 adjusted pH 3) = 10:5:85 solution, the detection wavelength was 254 nm, the flow rate was 1 ml/min, and the column temperature was 30 °C. The experimental results show that the chromatographic peak area of ​​chromium picolinate in the range of 0.232～1.16μg has a good linear relationship with the injection volume. The regression equation: y=2.27+1.96×103x, r=0.999 9.
In practice, the trivalent chromium content in the sample is generally used to evaluate the product quality, and there are many determination methods, such as atomic absorption method, ICP method, spectrophotometry, titration analysis, and the like. For example, on a one-tenth of an electronic balance, weigh about 25 mg of each of the various chromium chelate complex salts prepared above (in parallel) in a 100 ml flask, and add 2.5 ml of concentrated HNO 3 and 2 ml of concentrated HCl to the electric furnace. Digest with low heat, then evaporate most of the acid, cool, wash into a 100ml volumetric flask with water, dilute to volume and shake (the solution is blue with Cr 3+ ). The content of Cr was measured by a plasma emission spectrometer, and the Cr 3+ standard solution of 50 μg/ml was used as a standard, and the solution treated in the same manner as above was blank corrected. Jin Hao et al. determined the chromium content by atomic absorption method. Take 0.2-0.5g yeast dry powder sample in the digestive flask, add about 8ml HClO 4 - HNO 3 (4:1) mixture, and place the digestive bottle on the electric furnace. Digestion, the digestion can be stopped when the solution becomes colorless. The digest was transferred to a 10 ml volumetric flask and made up to volume with a 5.0% strength HNO3 solution. The test conditions were: lamp current I=12 mA, passband AA=1.6 nm, wavelength λ=357.8 nm, burner height=7.5 mm, air flow rate=9.4 L/min, acetylene gas flow rate=2.5 L/min. According to the standard curve, the chromium content in the sample to be tested can be obtained. Wang Qing et al. determined the chromium content in chromium (III) nicotinic acid by ICP method, and weighed 25 mg of chromium (III) nicotinic acid in a 100 ml flask, and added 2.5 ml of concentrated nitric acid and 2 ml of concentrated hydrochloric acid to the small furnace for digestion. After cooling, make up to 100 ml volumetric flask with water (the solution is blue of Cr 3+ ), measure with a plasma emission spectrometer, and use 50 μg/ml of Cr 3+ standard solution as the blank reagent.
Only Bingwen et al. used two capacity analysis methods to determine the chromium content in chromium nicotinate. 1 wet oxidation method. Weigh accurately about 2.000 0g sample, dissolved in 100ml water, 15ml of sulfuric acid - phosphoric acid mixture, heated to boiling, concentrated to a volume of about 30ml, at this time a green solution was a clear solution, cooled into 250ml volumetric flask, Add water to the mark and shake well. Pipette 25.00ml of the above solution accurately into a conical flask, add 1ml of 0.1mol/l silver nitrate solution and 10g/l manganese sulfate solution, heat to boiling and add solid ammonium persulfate several times until high manganese is formed. After the purple color of potassium acid, boil for another 10 to 15 minutes, add saturated sodium chloride solution until the purple color of the solution disappears, continue to boil for 10 minutes, and cool. Plus 8ml (1 + 1) sulfuric acid, 3-phenyl-anthranilic acid N- dropwise indicator, 0.100 0mol / l standard solution of ferrous ammonium sulfate titration solution by a cherry red to emerald green is the end. 2 dry oxidation method. Accurately weigh 1.500 0g sample in a crucible, add 5g sodium hydroxide and 3g sodium peroxide to mix. After carbonization to smokelessness on an electric furnace, the sample was placed in a box furnace, and after burning at 800 ° C for 2 hours, it was taken out and cooled. Dilute with 4 mol/l sulfuric acid and a small amount of water, transfer the leachate completely into a 250 ml volumetric flask, dilute to volume with water, and mix. Pipette accurately draw the liquid 50.00ml iodine flask, 1g of potassium iodide and 4mol / l 20ml of sulfuric acid, shake, placed in the dark for 10min, add 80ml water, 0.100 0mol / l standard sodium thiosulfate solution Titration, 5 ml / l starch solution indicator 3 ml was added at the near end point, and the titration was continued until the solution blue disappeared, and a blank test was performed. [next]
Most of the chromium in high-chromium yeast exists in the form of organic chromium, and the content of organic chromium is also one of the criteria for evaluating the nutritional value of high-chromium yeast. Ding Wenjun et al. Separated and determined organic chromium and inorganic chromium in high-chromium yeast. 0.2-0.3 g of yeast dry powder was added to a centrifuge tube containing 9 ml of distilled water, thoroughly stirred at intervals, and allowed to stand for 12 h, then 3 Centrifuge at 500 r/min for 20 min, repeat several times, and aspirate the supernatant to determine the inorganic chromium content by atomic absorption method. The lower layer precipitate is removed from the centrifuge tube, and the organic chromium content can be measured by digestion and constant volume.
3.2 Determination of the content of ligands in organic chromium products The content of ligands in organic chromium products is generally determined by high performance liquid chromatography. Wang Qing et al measured the niacin in chromium (III) nicotinic acid, weighed 30 mg of chromium (III) nicotinic acid in a 50 ml volumetric flask, added 500 mg of oxalic acid, and then added 3 ml of water, and heated on a boiling water bath until the solution was clear and presented. Blue (indicating that chromium in chromium nicotinate is Cr 3+ ). After cooling, 20 ml of 0.02 mol/l disodium edetate was added, and after shaking, 2 ml of 6 mol/l sodium hydroxide was added, and the volume was adjusted and shaken, and left for 30 min. After filtration, the filtrate was analyzed by high performance liquid chromatography. The analytical conditions were as follows. Column: Dupont SAX (250 mm high, diameter 4.6 mm); mobile phase: 0.1 mol/l potassium dihydrogen phosphate + 0.01 mol/l disodium edetate, pH 4.2; detection wavelength: λ = 261 nm; flow rate: 1.0 ml/min.
3.3 Determination of other components in organic chromium products Other components in organic chromium products, such as chloride, arsenic and lead, can be determined by reference to relevant feed standards. In particular, the content of arsenic and lead should be lower than the national allowable range for feed products. Since the production of organic chromium products, generally using chromium trichloride and niacin, picolinic acid, amino acid, citric acid and other organic ligands, by adjusting the pH with a base (caustic or soda) to obtain the product, it is bound to If a by-product such as sodium chloride is formed, the sodium chloride should be separated and removed, and the chloride ion content in the product should be low.
Therefore, whether the content of trivalent chromium ions and organic ligands is consistent; whether it is consistent with its molecular structure; the level of chloride ions in the product; the content of toxic elements such as arsenic and lead; the content of hexavalent chromium ions; An important criterion for evaluating the quality of organic chromium products.
In summary, extensive research on chromium-containing organic compounds has shown that it has a variety of extremely important active functions in living organisms. Chromium (III) chelates with relatively small stability constants and relatively high solubility will probably have a better nutritional effect on animals. With the deepening of people's research and the improvement of understanding, it is believed that chromium-containing organic compounds will play an increasingly important role in our lives. From the reports of the current test results, the application of organic chromium has achieved encouraging results, and organic chromium may become a new nutritional additive that can bring significant significance to human health and animal production.

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