There is a substance in plants, algae and other organisms in nature that humans and most animals cannot synthesize by themselves——CarotenoidsLutein is a carotenoid.Although there are more than 600 known carotenoids[2]However, only a small part can be absorbed and utilized by human tissues, including lutein.
Lutein in a broad sense refers to carotenoids xanthophylls II, which includes lutein and its isomers Zeaxanthin and mesozeaxanthin.Although their names are different, they all belong to xanthophylls II in essence, and can be transformed into each other and coexist in a certain proportion[3]。The main industrial source of natural lutein is the extraction and saponification of lutein ester in marigold to obtain lutein monomer[4]。
Lutein, as a natural plant pigment with multiple biological activities, has been widely used in food, medicine and cosmetics. However, because most of the lutein is unsaturated, it has poor water solubility and stability, is easy to be degraded and inactivated, and its oral bioavailability is low, which greatly affects its efficacy[5]。1g lutein is equal to the value of 1g gold[6], has been given the reputation of "plant gold".
Lutein can inhibit the proliferation and differentiation of preadipocytes, and play a role in reducing lipid.Specifically, it inhibits the activity of peroxisome proliferator activated receptor - γ (PPAR γ), a transcription factor responsible for activating fat cells.The activation of PPAR γ can down regulate the expression of inflammatory factors, such as TNF - α, LP and interleukin-6 (IL-6), and induce the expression of adiponectin (a fat factor that makes the liver and muscle sensitive to insulin), thereby regulating insulin sensitivity, intervening in adipocyte differentiation, and playing a role in reducing lipid.
2. Improve the visual function of patients with age-related macular degeneration (AMD) and healthy people[8]
Lutein is the main carotenoid in the retinal macula, which can filter blue light into the human retina to a certain extent, effectively reduce visual damage, inhibit the activity of oxygen free radicals, and prevent oxygen free radicals from damaging the visual cells.The exact cause of AMD is still unclear, which may be related to heredity, long-term light damage, metabolic and nutritional dysfunction and other factors.Lutein and zeaxanthin supplementation can improve the early dysfunction of central retina in early AMD patients.
3. Reduce the risk of cardiovascular disease in healthy people[8]
Lutein has a good antioxidant capacity, which can effectively inhibit the oxidative stress reaction in the process of atherosclerosis, thereby reducing inflammatory reaction and reducing oxidative damage to tissues and cells.The risk of cardiovascular disease will be reduced if the intake of lutein and the level of lutein in blood or fat tissue are high.
4. Slow down UV induced skin damage in normal people[8]
Lutein has the function of antioxidation and inhibition of lipoxygenase, which can reduce the erythema, aging, burns and even skin cancer caused by ultraviolet radiation on the skin.
5. Coloring egg yolks, poultry and chicken feed[9]
Lutein has strong coloring power, which can increase the hatching of eggs and the reproduction rate of birds.In many countries and regions of the world, especially consumers in the United States and many Asian countries, due to habits and psychological effects, most people prefer golden or orange yolks, golden skin birds, soft red meat, and often judge the nutritional value and freshness of eggs from the color of the yolks.According to experience, consumers regard yellow skin as the symbol of broilers with good meat quality and flavor, which directly affects the price of products.Therefore, in the modern poultry industry, in order to meet the needs of the market, feed companies often add excessive synthetic commodity colorants to feed, which not only increases the cost greatly, but also is harmful to human health[2]Therefore, lutein is also a natural pigment without side effects, which can color egg yolks, poultry and chicken feed.Because its safety and nutritional functions meet the market demand, it is widely used in feed coloring in various countries.
6. Anti cancer function
Lutein belongs to carotenoid, which has special physiological activity and can inhibit the growth of human tumors[10]It can resist various cancers, such as skin cancer, breast cancer, colon cancer, etc.
Factors affecting stability
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Influence of environmental factors on the stability of lutein[7]
oxygen
Because lutein contains many unsaturated double bonds, and two ionone rings are connected with hydroxyl groups, the most common reason for lutein degradation is oxidation.During the drying process of fruits and vegetables, lutein may be oxidized when exposed to air, leading to isomerization of lutein.Research findings[11]In addition to the most basic epoxidation and hydroxylation of lutein during processing, the direct rupture of lutein polyene chain will also form colorless small molecular compounds, and the biological activity of lutein will also be lost.[7]
temperature
Under heat treatment, the cell wall and cell membrane of spinach will be damaged, which will promote the dissolution of lutein, and the all trans conformation will be partially transformed into cis structure (9-cis and 13-cis lutein). Its stability will decline, which will lead to the degradation of lutein and reduce its biological activity.[7]
pH
Under different pH conditions, lutein will have different changes. Under extreme pH values lower than 4.0 or higher than 8.0, lutein will undergo deesterification and cis/trans isomerization, leading to degradation of lutein. Therefore, lutein is suitable for storage and reaction under neutral conditions[12]。
illumination
Light has obvious degradation effect on lutein. This is because light accelerates the oxidation of lutein molecular chain, and the carrier degrades and breaks, forming low molecular weight compounds, which make lutein lose color.At the same time, the stability of lutein decreases while the conjugated polyene chain of lutein is deporotonated and loses electrons[5]。
Extraction method
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At present, the extraction methods of lutein mainly include drying method, extraction method, microwave extraction method, extraction method, ultrasonic method, enzyme assisted extraction method, etc[13]。
Drying method
A new rotary drum dryer was used to hammer and dry marigold, and lutein was obtained from it.When the hammering ratio is different, the hammering efficiency fluctuates between 70% and 90%.The amount of lutein depends on the length of drying time;Under the same drying time, the lutein content obtained by drying at 60 ℃ is more than that at 70 ℃[14]。
extraction method
Use supercritical COtwoLutein is extracted from marigold by fermenting, drying and crushing marigold flowers as raw materials, ethanol as entraining agent, and supercritical COtwoThe method of extracting marigold extract, saponifying marigold extract through potassium hydroxide, and finally obtaining water-soluble natural edible pigment lutein resin[14]。Supercritical COtwoLutein obtained by extraction method has no residual solvent, which reduces the toxicity to human body and environmental pollution during the extraction process. COtwoThe gas is cheap and easy to obtain, non-toxic, safe, low cost, easy to separate, and fast to extract.The extraction method has the advantages of simple process, low energy consumption, environmental protection, high product purity, positive color, good heat and light resistance, and stable color.
Microwave extraction method
Microwave is a kind of instantaneous penetration heating mode, which breaks the plant cell wall under the action of microwave field, thus accelerating the extraction rate and effectively improving the yield[15]。
Leaching method
The process mainly includes raw material pretreatment, crushing, extraction, filtration, concentration, drying, etc. The solvents used are different according to different pigments and raw materials[16]Generally, tetrahydrofuran is used for treatment.
Ultrasonic method
Ultrasound can generate and transmit powerful energy. High energy ultrasound acts on the liquid. When the liquid is in a sparse state, the liquid will be torn into many small holes. These holes will be closed in an instant. When they are closed, instantaneous high pressure will be generated, that is, cavitation effect.The great pressure generated by the cavitation effect of ultrasonic wave causes the cell wall of the crushed object and the whole organism to be broken, and the whole breaking process is completed in an instant.At the same time, the vibration generated by ultrasound strengthens the release, diffusion and dissolution of intracellular substances, which is conducive to the extraction of intracellular effective ingredients[17]。Ultrasonic method can make the lutein in marigold flower fully dissolved, improve the dissolution rate, shorten the extraction time, and have high extraction efficiency. It eliminates the impact of high temperature on the extraction components, saves the consumption of solvent, and has gradually replaced the traditional extraction methods.
Enzyme assisted extraction
Enzyme assisted extraction method is to use cellulase to treat the cell wall with high lutein content, such as marigold, to destroy the structure of the cell wall, so that the organic solvent can quickly enter the cell for easy extraction[18]。Enzyme assisted extraction method can improve the extraction rate of lutein because of the activity of enzyme medium.
