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    Home > Biochemistry News > Plant Extracts News > Absorption and metabolism of Soybean Isoflavones

    Absorption and metabolism of Soybean Isoflavones

    • Last Update: 2020-04-03
    • Source: Internet
    • Author: User
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    2015-01-24 classification: efficacy 0 people commented that soybean isoflavones are secondary metabolites formed in the growth process of soybean The content of isoflavones in soybean seeds is 0.05% ~ 0.7%, mainly distributed in cotyledons and hypocotyls of soybean seeds, and very few in seed coat For a long time, soybean isoflavone has been regarded as a bad component in soybean However, recent studies have shown that soybean isoflavones can prevent and even cure cancer, arteriosclerosis, osteoporosis and menopausal syndrome In nature, isoflavone resources are very limited Soybean is the only food resource that contains isoflavone and its content is meaningful in nutrition, which endows soybean and soybean products with special importance At present, there are 15 kinds of soybean isoflavones, which can be divided into free aglycones and binding glycosides Aglycones account for 2% - 3% of the total, and glycosides account for 97% - 98% of the total Three isoflavones, genistein, daidzein and glycinten, have been isolated and identified In soybean seeds, 50% - 60% of isoflavones are genistein, 30% - 35% are daidzein, 5% - 15% are daidzein Isoflavones in soybean mainly exist in the form of gametophyte, and its aglycon form shows much higher activity than the gametophyte In addition, the absorption of isoflavones in different forms is also different, and their gametophytes are almost not absorbed The digestion and absorption pathway of soybean isoflavone in human body is not completely clear According to the structure of soybean isoflavone metabolic intermediates isolated and identified from human blood and urine, it can be inferred that the absorption and metabolism pathway of soybean isoflavone in human body should be basically the same as that of other animals 1 The experiment of soybean isoflavone absorption in human body shows that soybean isoflavone is mainly absorbed in intestine, and the absorption rate is 26-40% According to its structure, the absorption pathway of soybean isoflavone can be divided into two ways: direct absorption by small intestine and absorption by colon wall after degradation ① The liposoluble dorsal element can be directly absorbed from the small intestine, but the mechanism is not clear It is estimated that the small liposoluble and molecular space structure of aglycone can be directly absorbed by the passive diffusion of villous epithelial cells on the small intestine wall It is also believed that the absorption of soybean isoflavone in the small intestine is through active transport, and the main proteins involved are glycosyltransferase and lactose dehydrogenase( LPH) ② Most of the isoflavones in the food containing soybean and its products are in the form of glycosides, which can not pass through the wall of the small intestine During the process of intestinal peristalsis, they are hydrolyzed by the p-glucosidase or p-galactosidase of bacteria and microorganisms in the colon, and the products are further degraded by cells to generate aglycones, which are absorbed into the blood by the wall of the colon The absorption of soybean isoflavone is closely related to the types of microorganisms in human intestine The Lactobacillus B congensis distributed in the lower intestine and the large intestine can secrete β - glucosidase, which is conducive to the hydrolysis and absorption of isoflavone glycosides On the contrary, aostridia bacteria in the intestine can remove the C-ring of isoflavone and destroy the original structure of isoflavone in anaerobic environment Steesma et al Showed that genistein, daidzein and their glycosides could be transported by Caco-2 cells of small intestine endothelium in vitro In this study, Caco-2 cells were cultured on the semipermeable membrane The integration of Caco-2 monolayer cells was measured by the endothelial transfer resistance meter, and the permeability of Caco-2 monolayer cells was quantitatively analyzed by PEG2000 The results showed that 30% - 40% genistein and daidzein were transferred from the top to the base after 6 hours of administration, and the level of transport was maintained for 24 hours It has endogenous p-glucosidase activity Wihiamson et al Found through human metabolism experiment that after consumption of genistein and daidzein, two absorption peaks of daidzein appeared successively in plasma, the first peak appeared between 30-60min, the peak height was lower, the peak area was smaller, accounting for 30% of the total absorption; the second peak appeared 6-9h, the peak height was higher, the peak area was larger, accounting for 70% of the total absorption It is believed that colon is the main site of soybean isoflavone digestion and absorption 2 The metabolism study of soybean isoflavones confirmed that the liver plays a key role in the metabolism of soybean isoflavones UDP glucuronosyltransferase in liver microparticles has the effect of glucuronization, sulfation or methylation on isoflavones in rabbits It has been considered that soybean isoflavones are mainly combined with glucuronic acid, while the content of conjugates formed by combining with sulfuric acid is less Aglycones and conjugated products can be secreted into the intestinal cavity with bile, hydrolyzed to produce aglycones under the action of debonding enzyme produced by colonic microorganisms, and then recombined into human blood At the same time, most of the flavonoids are degraded and metabolized by intestinal microorganisms through heterocyclic cracking The products can be absorbed into the blood and then discharged from the urine, but the urine output only accounts for 7% - 30% of the absorption, and the unabsorbed part is discharged with the feces Recent studies on pharmacokinetics of genistein in rats suggest that dietary soybean isoflavone can also be secreted through bile, because it can be detected in bile in a very short time after oral administration of genistein The blood concentration of soybean isoflavones is related to daily intake, and the concentration of genistein in the blood of most Asians with high intake reaches a high level Kelly et al Detected the isoflavone metabolites in the urine of 12 volunteers after ingesting the soybean meal, and confirmed that there were genistein, daidzein, daidzein and their metabolites in the urine, indicating that some of them were excreted through the kidney, and some of them were secreted from the liver to bile, forming the circulation and excretion of the liver and intestine The microorganisms in the kidney and intestine degrade the parent nucleus of soybean isoflavone into a relatively simple phenolic component It was found that those with abnormal renal function could not excrete soybean isoflavones Under the degradation of bacteria, daidzein in urine and intestines continues to be reduced to the intermediate products such as dihydro daidzein and isoflavane-4-ol by microorganisms, and the final metabolite is stable estriol There are also a small amount of daidzein by the role of microorganisms, untie the ring to become oxygen demethylation of sandalwood But genistein, which was not absorbed, was finally degraded to 4-ethylphenol without estrogen activity Some researchers found that the urine of soybean products given to uremic patients was free of estriol and 4-ethylphenol HPLC analysis showed that there were 4-ethylphenol in the plasma and urine of the animals taking genistein orally The metabolism of genistein was studied with 13C labeled genistein It was found that there was a linear relationship between the content of 4-ethylphenol in the plasma and urine and the content of human isoflavone Fritz's research proved that soybean isoflavone can be detected from the milk of Oriental women by RP-HPLC, which proved that soybean isoflavone can be secreted through the milk The content of genistein in milk of white women was higher than that of Daidzein in Franko's study, while that of Chinese women was the opposite The content of isoflavones in human milk is not high, even in some experiments, it can not be detected It can be seen that infants can obtain a certain amount of isoflavones from breast milk, but the amount is not much Pregnant mothers can also pass soybean isoflavones to their offspring through umbilical vein and amniotic fluid, which is an important factor that affects and reduces the risk of cancer in the life of Oriental children.
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