Luteolin is a natural flavonoid compound, which was originally named from the branches, leaves and stems of the genus in R.odorata L. Luteolin is widely present in plants in the form of glycosides and can be isolated from more than 300 species of plants. Peanuts, Brassica napus, oleaveuropaea, buckwheat, cocoa, pepper, Apium graveolens, Daucus carrots, cucumbers, lettuce, pomegranates and other crops and fruits and vegetables contain luteolin. In addition, honeysuckle, carnation, Perilla frutescens, Scutellaria baicalensis, Menthax piperita, thyme, oregano, rosemary, Wedelia chinensis, artichoke, Capparis spinosa, Dracocephalun subapitatum, Ajuga reptans, Impatiens textori also contain luteolin.
Although luteolin is rich in plants, but the absolute content is low. In different plants or the same plant in different parts, the content of luteolin is different. The study found that the shell of Tamarindus indica contains luteolin, but it was not detected the luteolin in its flesh. The seeds, stems and leaves of peanut did not contain or contain only a small amount of luteolin, but the content of luteolin in the shell was relatively high, and the content of luteolin in the fruit shell was also different (0.02% ~ 0.475%). There were also significant differences in the content of luteolin in the same peanut cultivars grown in different areas. The content of luteolin in the fruit, middle type, pearl bean type and multi-grain peanut was higher than that of the wild type The content of luteolin was the highest in the middle peanut cultivars (0.475%).
Luteolin is one of the most common flavonoids. It has a preventive effect for cancer, cardiovascular disease and other human diseases, and has anti-oxidation, anti-bacterial, anti-tumor, anti-inflammatory and other biological activity, which has a wide range of pharmaceutical value and good prospects for development. Luteolin has a dual application value in human health and plant resistance. It has become one of the hotspots in the development and utilization of natural medicine and plant pathology at home and abroad. Peanut husk is rich in luteolin, which is one of the most important sources of luteolin. The development of the use of peanut shells of luteolin and other natural flavonoids, can improve the peanut Comprehensive utilization value.
Bioactivity of luteolin
Luteolin is a natural flavonoid, which has several biological activities and is beneficial to human health. Luteolin on the human body’s biological function is mainly manifested as: anti-oxidation, anti-bacterial, anti-inflammatory, anti-tumor, anti-radiation, but also has the effect of relieving hypertension, antitussive and expectorant.
(1) oxidation resistance
The free radicals in the body are closely related to cell aging, cancer, atherosclerosis, thrombosis and many other diseases. Luteolin and other natural flavonoid compounds have the role of scavenging free radicals. Through the phenolic hydroxyl and free radical reaction, it can produce chemical stability of the semi-quinone free radicals to terminate the free radical chain reaction with antioxidant activity. Furthermore, luteolin can inhibit the activity of lactate dehydrogenase, malondialdehyde and other substances in cardiomyocytes, and enhance the activity of antioxidant enzymes, such as SOD and CAT.
(2) anti-tumor
Luteolin has anti-tumor, anti-cancer biological activity. Luteolin can induce tumor death in a variety of ways, play a role in the removal of malignant tumor cells, and will not induce healthy peripheral blood mononuclear cells in the event of programmed death. In addition, luteolin can inhibit the expression of vascular endothelial growth, reduce tumor angiogenesis, thereby limiting the growth and metastasis of tumor cells. Luteolin can be used as sensitizer for radiotherapy and chemotherapy, synergistically inhibit the growth of tumors. When combined with chemotherapeutic drugs, it can improve the sensitivity of tumor to chemotherapeutic drugs and enhance the ability of drug to induce tumor cell apoptosis.
(3) anti-inflammatory
Studies have shown that luteolin has anti-inflammatory biological activity.COX, LOX and INOS are important proinflammatory enzymes, and luteolin can inhibit COX-2, LOX, INOS and other activities with anti-inflammatory effect.
(4) antibacterial
Luteolin and other flavonoids have an important role in resisting foreign microbial invasion. Although luteolin has the effect of resisting the invasion of exogenous substances, in the rhizobia and legumes symbiotic conditions will promote the synthesis of luteolin.
(5) other biological activity
Luteolin has anti-radiation activity, which can reduce the radiation induced ROS caused by plant and animal damage. Luteolin can reduce the body’s blood pressure and cholesterol levels to prevent the occurrence of cardiovascular disease and reduce the concentration of blood glucose in the body to reduce the risk of diabetes In addition, luteolin can also be through a variety of different metabolic mechanisms to reduce the formation of histamine with anti-allergic effect.
3 Biosynthetic Pathways and Synthetic Methods of Luteolin
3.1 luteolin and other flavonoid biosynthetic pathway
Luteolin and other flavonoids are products synthesized by shikimic acid pathway and polyketone pathway. The basic skeleton of flavonoids is produced by three Malonyl-CoAs and one Coumaroyl-CoA.
3.2 Artificial Synthesis of Luteolin
（1）Total synthesis method
The total synthesis process of phloroglucinol has been reported. However, the total recovery rate is low (3% -4%).
(2) Semi-synthetic method
Rutin was used as raw material to dissolve rutin under alkaline conditions and sodium dithionite was added. The solution was heated and refluxed at 100°C for 12h to hydrolyze and obtain luteolin of purity of more than 95%. The yield was about 56%. Using microwave technology, rutin as raw material can be simple and efficient synthesis of luteolin, the yield can be as high as 60%. The improved microwave synthesis method can obtain 95% purity of luteolin, the yield can be increased to 83.9%. However, rutin itself has a good role in health care, and its lack of sources, extraction and purification costs are high.
（3）Biosynthesis
According to the physical and chemical properties of luteolin and the biosynthesis mechanism of flavonoids, although a variety of artificial methods can be used to synthesize luteolin, by the production of raw materials, recovery process, production cost control and environmental protection, safety factors, the development prospect of synthetic luteolin is far less than that of natural luteolin.
4. Outlook
Luteolin is a flavonoid compound, which has a variety of biological characteristics, such as anti-cancer, anti-oxidation, anti-bacterial, and other immune benefits. Peanuts, carrots, pomegranates and other hundreds of plants contain a certain luteolin. This class of compounds not only makes these plants have a good health care value, but also plays an important role for plant itself against foreign microbial infection. Luteolin and other flavonoids are one of the research hotspots in the fields of phytochemistry, food processing, medicine and health care, and plant resistance improvement.