Lutein What Is It?

Lutein exists in nature together with zeaxanthin. Natural lutein esters are an important carotenoid fat ester, which is more stable than free lutein. The body also absorbs it better than free lutein. The bioavailability of lutein esters in the body is 1.6 times that of lutein. The Ministry of Health approved lutein ester as a new resource food in 2008. Therefore, both lutein and lutein ester can be used as functional factors in new health foods and food additives, and their application prospects are broad.

1 Physical and chemical properties and sources of lutein

1.1 Physical and chemical properties of lutein

Lutein, also known as phyto-lutein or xanthophyll, is a tetraterpenoid compound widely found in animals and plants [1]. Its molecular formula is C40H56O2 and its relative molecular weight is 568.87. Lutein is an orange-yellow powder, a paste or a yellow-brown liquid with a weak hay-like odor. It is insoluble in water, but soluble in propanol, methanol, isopropanol and dichloroethane, and has good heat resistance.

1.2 Sources of lutein

Lutein is widely found in green vegetables, corn and egg yolks, and is most abundant in spinach, kiwifruit and carrots. Studies have found that egg yolks and corn have the highest levels of lutein and zeaxanthin, up to 85% of the total carotenoids, and corn has the highest level of lutein (60% of the total carotenoids). In addition, darker vegetables and fruits such as zucchini, papaya, oranges, and pumpkins also contain some lutein. In recent years, it has been discovered that marigolds are rich in carotenoids, especially lutein. The South American company Henkle has extracted lutein esters from the resource-rich pumpkin and orange residue after juicing, which can be automatically converted into lutein in the human body. Nowadays, marigolds, corn protein powder and algae have become the main sources of lutein extraction.

1.2.1 Marigolds

Marigold, also known as calendula, is an annual herb native to Mexico. Marigold flowers come in yellow, orange, and red petal colors. Marigolds were first introduced to China in the 1980s and are now grown in large quantities, making them the main source of lutein. The American company Kemin Foods was the first to invent a new process for producing lutein, making it a new type of health food additive. The company extracts the finished lutein crystals from large quantities of wild marigolds from all over the United States. Li et al. [3] studied the lutein content of 11 different varieties of marigolds and found that the lutein content varied greatly, with the highest content reaching 611.0 mg/100g and the lowest 161.0 mg/100g. This indicates that the lutein content in marigolds varies greatly. Bhattacharyya et al. [4] studied the antioxidant properties of lutein in three different colors of marigolds (orange, yellow, and red). They found that the antioxidant properties of lutein in orange marigolds were the highest, and the lutein content was also higher than that of the other colors.

1.2.2 Corn gluten meal

Corn gluten meal, also known as corn gluten powder, is a by-product of the production of corn starch and alcohol processing. It is obtained by drying the protein slurry separated from the crude starch milk produced by wet milling of corn kernels through a starch separator. It is mainly composed of corn protein, contains a small amount of starch and cellulose, and more importantly, is rich in lutein, zeaxanthin, β-carotene, etc. Corn is one of the world's three major food crops. Every year, a large amount of corn gluten is used as feed, which is an important source of lutein. Therefore, by secondary processing of corn, waste is turned into treasure. Extracting lutein from medical protein powder has become a current Corn is one of the world's three major food crops, and every year a large amount of corn gluten is used as feed, which is an important source of lutein. Therefore, through secondary processing of corn, waste is turned into treasure. Extracting lutein from medical protein powder has become a research topic today.

1.2.3 Algae

Extracting lutein from marigolds is a complex project. Growing marigolds requires not only a lot of land and manpower, but the lutein content in marigolds also varies greatly, with some reaching 0.03%. How to screen for high-yield lutein is a tricky problem, so from an economic point of view, marigolds are not the most ideal source of lutein. Nowadays, researchers are turning their attention to algae, because not only do algae contain lutein, they also grow fast and are easy to breed, which greatly improves the efficiency of lutein production. Lutein has been extracted from many algae, such as Muriellopsis sp and Chlorella zofingensis, and it is believed that algae will soon become the main source of industrial lutein production.

2 Functions of lutein and its mechanism of action

2.1 Coloring function

Lutein powder has a good coloring effect. Because it has a bright yellow color, it is insoluble in water, soluble in oil and ethanol, has strong coloring power, and is resistant to light, heat, acid, and alkali. It can be widely used to color pastries, candies, seasonings, pickles, and feed. It can also be used to color health products and sugarcoat tablets and color capsules. Lutein, as a natural yellow pigment, has the advantages of strong coloring ability, good stability and high safety. It has been listed as a food coloring agent in Europe and the United States. It can be used to give food a beautiful golden yellow color and can replace chemically synthesized lemon yellow, gardenia yellow, etc.

Adding lutein to feed can make the skin color of animals become brighter through continuous deposition. Compared with other colorants, lutein has the advantages of good stability, strong persistence, low damage and high safety. Zhou Liangjuan et al. Adding lutein to feed can make animals' skin color become brighter through continuous deposition. Compared with other colorants, lutein has the advantages of good stability, strong persistence, low damage and high safety. Zhou Liangjuan et al. [5] found through experiments that lutein can significantly improve the coloring of broiler shanks. Leng Xiangjun et al. [6] conducted a study on the effect of lutein on the body color of goldfish. By testing the changes in water, fat and protein in the muscles of goldfish, they found that lutein did not affect the composition of goldfish muscles, and that adding an appropriate amount of lutein could also improve the survival rate of goldfish.

2.2 Anti-cancer function

Domestic and foreign studies have shown that lutein has an inhibitory effect on breast cancer, esophageal cancer, skin cancer, prostate cancer, etc., and can effectively inhibit the proliferation of HepG2 cells. The mechanism may be related to regulating oxidative stress levels, inhibiting ATP production, and up-regulating the expression of bax mRNA and p53 mRNA. Wang Ruozhong et al. [7] used the HepG2 human liver cancer cell line and the L02 normal human liver cell line as research subjects, and observed cell survival rates by adding different doses of lutein. The experiment showed that adding a certain amount of lutein can significantly reduce the survival rate of cancer cells. Professor Mark Chark of Harvard Medical School in the United States and others investigated baby food and found that while carotenoids were 7.83 mg/l00g in ordinary foods, lutein only accounted for 4%. Carotenoids can reduce oxidative damage to DNA, and lutein, as one of the five important carotenoids in human blood and tissues, can accelerate cell fusion and improve the body's immunity. Fu Lei et al. [8] treated HT29 cells with different concentrations of lutein (20, 40, 80, 160 mg/L) and found that lutein could inhibit the proliferation of HT29 cells. Research results from the New York University School of Pharmacy show that the incidence of breast cancer is closely related to lutein intake. The incidence of breast cancer in the experimental group with low lutein intake was found to be 2.08 to 2.21 times that of the high intake group. Therefore, dietary lutein intake can inhibit and prevent the occurrence of tumors.

2.3 Protects eyesight

Studies in recent years have shown that lutein and zeaxanthin can prevent light damage to a part of the retina in the eye. There are two mechanisms involved.

(1) Lutein can filter high-energy visible blue light. Experiments have shown that reducing blue light by 40% can greatly reduce the amount of free radicals on the retina [9].

(2) As an antioxidant, lutein can reduce the oxidative effect of light on the eyes and control the formation of reactive oxygen species and free radicals. Lee et al. [10] studied whether lutein can reduce the impact of ultraviolet light on the body. The experiment found that the swelling of the ears in mice fed a diet containing lutein was significantly reduced compared to the control group, The experiment further found that the number of free radicals produced by mice with lutein in their diet under UV irradiation was lower than that of the blank group. This shows that lutein can reduce the photodamage to the skin caused by light as well as some pathological reactions, such as ear swelling.

Age-related macular degeneration (AMD), also known as senile macular degeneration, is one of the main eye diseases that threatens the sight of middle-aged and elderly people. Epidemiological studies have shown that the incidence of AMD is negatively correlated with the body's lutein content. Many experiments have also shown that lutein can reduce the incidence of AMD. Bone et al. [11] compared people with AMD and those without AMD and found that the lutein content in the eyes of people with AMD was lower than that of people without AMD, thus confirming the preventive and control effect of lutein on AMD. Researchers at the University of New Hampshire investigated the relationship between various factors in 278 volunteers and found that lutein in the diet and lutein in the blood were positively correlated with the macular pigment density in the eyes. They also proved that adding lutein to the diet can increase the macular pigment density in the eyes and reduce the risk of AMD. A clinical study conducted by Dr. Schuart Richard of the North Chicago Medical Center Ophthalmology Clinic of the American Optometric Association Journal on patients with age-related macular degeneration showed that taking 6 mg of lutein daily can reduce the risk of macular degeneration [12].

2.4 Antioxidant function

Currently commonly used synthetic antioxidants such as BHT, BHA, TBHQ, etc. can cause enlargement of the liver in animals. BHT can also increase the activity of microsomal enzymes. BHA has also been found to have carcinogenic potential. Therefore, restrictions have been placed on the use of synthetic antioxidants at home and abroad, and natural antioxidants have begun to be valued and favored. Lutein, as a type of carotene, contains multiple unsaturated double bonds and has a strong free radical scavenging effect. It can play an antioxidant and delay the effects of aging. Li Jinsheng et al. [13] studied mice fed with different amounts of lutein. The blank group was not added lutein. The results showed that lutein can significantly reduce the serum MDA level and increase SOD activity in model mice. Zhang et al. [14] applied lutein to Drosophila melanogaster to observe the effect of lutein on Drosophila melanogaster and analyze its mechanism. The results showed that 0.1 mg/mL lutein can extend the lifespan of Drosophila melanogaster from 49.0 d to 54.6 d. It was observed that compared with the control group, the MDA in Drosophila melanogaster decreased while the activity of antioxidant enzymes increased. It is inferred that lutein can extend the lifespan of Drosophila melanogaster by enhancing the activity of antioxidant enzymes.

3 Extraction and preparation methods for lutein

Most of the lutein in marigolds is bound to lauric acid, myristic acid, palmitic acid and stearic acid to form lutein esters. In corn protein powder, most of the lutein is present in the form of a complex with the protein. Denaturing the protein with a solvent such as ethanol can quickly extract the lutein. The traditional method of extracting lutein is generally to extract it by organic solvent extraction. After extraction with organic solvents such as ethyl acetate and n-butane, lutein monomers can be separated from the salts to obtain purer lutein monomers. To improve extraction efficiency, organic solvent extraction methods are often assisted by ultrasound, microwaves or enzymes. In addition, supercritical carbon dioxide extraction has also been applied to the extraction of lutein as a new method.

3.1 Organic solvent extraction

Organic solvent extraction is the most commonly used extraction method and is widely used in the extraction of lutein. Marigold flowers can be made into marigold particles through fermentation, pressing, drying and other processes, and then the pigment essential oil can be prepared by solvent extraction. Sheng Aiwu et al. [15] studied the effect of different extraction solutions on the extraction rate of lutein from dried marigold flower powder and found that the highest extraction rate of lutein, up to 6.21 mg/L, was achieved by extracting the pollen with a complex reagent of ethane, acetone and methanol. However, there are two disadvantages to the organic solvent extraction method. First, due to the toxicity of some organic solvents, there is a safety issue as the prepared lutein monomers may contain residues of the organic solvent. Second, the extraction rate is low.

3.2 Ultrasonic-assisted extraction

Ultrasonic-assisted extraction makes use of the principle of ultrasonic waves to break up cells during the extraction process, so that the extract can quickly and efficiently enter the extraction solvent, thereby shortening the extraction time and improving the extraction efficiency. Li Dajing et al. [16] studied the process of ultrasonic-enhanced organic solvent extraction of lutein from marigold flower powder, and concluded that the extraction rate of lutein can reach 93.65% under the conditions of an ultrasonic power of 300 W, ultrasonic action for 30 min, and a liquid-to-solid ratio of 1:20. Li Xiuxia et al. [17] studied the ultrasonic extraction process of lutein from corn protein powder, and the optimal process parameters were an ultrasonic time of 11 min, an initial temperature of 25.4 °C, and a liquid-to-solid ratio of 6.4 mL/g. Under these conditions, the lutein extraction rate could reach 67.90 μg/g. Li Man et al. [18] investigated the optimal process conditions for the extraction of lutein esters with the aid of ultrasonic waves in an organic solvent. An extraction rate of 18.57% was achieved at an ultrasonic power of 150 W, an extraction temperature of 40 °C, and an extraction time of 90 min.

3.3 Enzyme-assisted extraction

Enzymes can break down cell walls, thereby enabling the extracted substances in the cells to quickly combine with and exchange with the external solution, which can greatly improve the extraction efficiency. Li Dajing et al. [19] used marigold flower powder as the raw material and extracted lutein using a method that combined liquid cellulase treatment and organic solvent extraction. The extraction rate could reach 92.37%, and the enzyme method greatly improved the extraction efficiency compared to the solvent method alone (extraction rate of 77.53%).

3.4 Microwave-assisted extraction

Microwave-assisted organic solvent extraction has the advantages of high speed, high extraction rate, low solvent volume required, and simple operation compared to solvent extraction. Li Jianying et al. [20] studied the extraction of lutein from citrus peel by microwave heating and obtained an extraction rate of 71.60% under microwave power of 800 W.

Whether it is enzymatic, ultrasonic or microwave-assisted, the aim is to quickly release the contents of the cells. Therefore, some researchers have also studied the effect of cell disruption using different instruments on the lutein extraction rate. Chan et al. [21] compared three different methods of disrupting microalgae cells: an autoclave, ultrasonic cell disruptor and bead mill homogenizer. The samples were saponified and the lutein content was analyzed by HPLC. The results showed that the lutein extraction rate using the bead mill homogenizer (extraction rate of 2.8 mg/g) was significantly higher than the other methods.

3.5 Supercritical carbon dioxide extraction

Since the commonly used organic solvent extraction method has the problem of solvent residue, it can generally only be used as a feed additive. Supercritical carbon dioxide extraction can solve this problem. Supercritical carbon dioxide extraction uses supercritical carbon dioxide, which has a special solubilizing effect on certain substances, so that components with different polarities, boiling point, and molecular weight of the ingredients can be extracted separately. Supercritical carbon dioxide extraction has the advantages over other traditional methods of no solvent residue, no pollution, can avoid thermal degradation of the extracted substance at high temperatures, and can maintain the natural activity of the extracted substance. It can be used to prepare lutein with less solvent residue and high activity.

Tong Wanbing et al. [22] used corn protein powder as a raw material and extracted lutein using supercritical carbon dioxide extraction technology. The optimal process conditions were determined to be an extraction time of 2.3 h, an extraction temperature of 42 ℃, an extraction pressure of 30 MPa, and an entraining agent of 90% ethanol (added at a rate of 5 mg/100 g). Under these conditions, the corn lutein purity predicted by response surface analysis can reach 46.5%. At present, many people have extracted lutein by supercritical extraction, and conditions are constantly being optimized. However, due to the relatively high cost of the supercritical extraction method, it has not been applied to the large-scale production of lutein. There is not much relevant literature, but as a green and efficient extraction technology, supercritical carbon dioxide extraction technology has great potential in the extraction of lutein.

4. Application of lutein in food processing

Lutein has been used as a green and healthy food additive in the fields of food and medicine. According to researchers at the University of Ljubljana in Slovenia, adding lutein to sunflower oil and then heating it can help reduce the trans fatty acids produced by the oil at high temperatures. This effect is significantly better than adding rosemary extract to the oil. The researchers added rosemary extract and lutein to sunflower oil, then heated the sample oil together with a control oil to 180 °C. Afterward, the trans fatty acid content of each oil after heating was measured. Compared with before heating, the control oil, the sample oil with rosemary extract, the sample oil with lutein added, the content of trans fatty acids with more than one trans double bond increased from 0.91% to 1.71%, 1.55%, and 1.43% respectively after heating.

Lutein is also used as a nutritional supplement and coloring agent in beverages and jellies. Adding lutein to orange juice drinks, dairy drinks, and carbonated drinks can maintain more than 90% of lutein after 6 months of storage. Li et al. [23] used xylitol and lutein as raw materials, and prepared a xylitol-lutein solid beverage through processes such as crushing, mixing, granulating, and whole grain processing. By combining low-energy xylitol with fatigue-fighting lutein, the health benefits of the beverage were enhanced. By preparing lutein into lingonberry lutein ester soft capsules, it was found through experiments that after 45 days of use, the test group had significant improvement in symptoms such as eye pain, eye swelling, photophobia, blurred vision, and dry eyes. Now this capsule has been successfully applied in the field of health food. [24］

5 Conclusion

Lutein is not only a natural coloring agent, but also has a variety of health functions such as protecting eyesight, anti-oxidation and slowing down aging, improving immunity, and anti-tumor. With the increase in consumer demand for natural, green, and healthy foods, the potential market sales value of natural lutein is huge. At present, a variety of lutein foods have been developed at home and abroad, such as Amway Bilberry Vision Protect and Improve Tablets (containing carotene, vitamin A and lutein) produced by Nutrilite in the United States, 2nd Generation Lutein Blueberry Capsules produced in Germany, lutein ester gummies produced by Xiuzheng Pharmaceutical, Lutein tablet candy produced by North China Pharmaceutical Group, Embilute lutein blueberry chewable tablets produced by Xuancheng Biowellness Bioengineering Co., Ltd., and the functional food supplement lutein for humans, the so-called “Super Vision Drink-Flora,” produced by Kemin Foods Inc. in the United States, has been launched. This is a water-soluble beverage product containing “GLO lutein.” American Hutz Manufacturing Company, Swiss Roche Company, and German MAR-CUS Company are also engaged in the research, development, and production of lutein health foods, and the market prospects are broad. However, China currently needs to strengthen its research on the functional mechanism, dose-effect relationship, and application of lutein.

(1) Although lutein and lutein esters are abundant, due to China's large population and limited land resources, the extraction of lutein from plant resources is limited. It is necessary to focus on the extraction of lutein from agricultural and sideline products such as corn yellow powder, fruit and vegetable processing by-products such as pomace, peels, and vegetable scraps. Lutein can be produced on a large scale and in an industrialized manner using efficient production methods such as algae cultivation and microbial fermentation.

(2) In addition to its good coloring function, lutein also has the functions of protecting eyesight, anti-oxidation, preventing tumors, inhibiting tumor growth, and delaying arteriosclerosis in the human body. It can also reduce the generation of trans fatty acids during the processing of vegetable oils. However, the specific mechanism of action and the quantitative effect need to be further explored.

(3) Study the synergistic effect of lutein and lutein esters with other antioxidants such as β-carotene, vitamin E, vitamin C, lycopene, polyphenols, etc., to develop highly effective food antioxidants and antioxidant anti-aging health foods; research the synergistic effect of lutein and other functional ingredients such as anthocyanins, vitamin A, β-carotene, bioactive polysaccharides, active peptides, etc., to develop health foods that protect eyesight, prevent tumors, and improve immunity.

 References

[1] Gu Kun, Chen Jingbo, Liu Mei, et al. Study on several degradation reactions of lutein [J]. Chemical Research and Application, 1999 (5): 543-544.

［2］Sommerburg O，KenunenJ E，Bird A C，et al.Fruits and vegetables that are sources for lutein and zeaxanthin：the macular pigment  in human eyes［J］.The British Journal of Ophthalmology，1998（8）：907-910.

［3］Li Wei，Gao Yanxiang，Zhao Jian，et al.Phenolic，flavonoid，and lutein ester  content   and  antioxidant  activity  of  11  cultivars  of  chinese  marigold ［J］.Journal of Agricultural and Food Chemistry，2007（21）： 8478-8484.

［4］Bhattacharyya Sugata，Datta Sanjukta，Mallick Bidisha.Lutein content and in vitro antioxidant activity of different cultivars of Indian marigold flower（Tagetespatula L.）extracts［J］.Journal of Agricultural and Food Chemistry，2010（14）：59-64.

[5] Zhou Liangjuan, Ji Cheng, Li Yuxin, et al. Study on the coloring effect of several natural lutein on three yellow broilers [J]. Feed Industry, 2003 (4): 36-40.

[6] Leng Xiangjun, Shi Yanzhi, Li Xiaoqin, et al. Effect of lutein added to feed on the body color of goldfish [J]. Journal of Zhejiang University: Agriculture and Life Sciences Edition, 2010 (2): 168-174.

[7] Wang Ruozhong, Shen Xinnan, Shi Dongyun, et al. Research on the inhibitory effect and mechanism of lutein on human liver cancer cells HepG2 [J]. Journal of Nutrition, 2012 (4): 332-335.

[8] Fu Lei, Liu Lei, Zhang Nan, et al. Lutein inhibits the proliferation of SGC-7901 cells and induces apoptosis [J]. Chinese Journal of Pharmacology, 2009 (7): 216-221.

［9］Moeller S，Parekh N，Tinker L,et al.Associations between intermediate  age -related macular degeneration and lutein and zeaxanthin in the  carotenoids in age-related eye disease study（CAREDS）［J］.Ancillary  Study of the Women's Health Initiative Arch Ophthalmic，2006（124）： 1151-1162.

［10］Lee Erica H，Faulhaber Dorothea，Hanson Kerry M，et al.Dietary lutein  reduces ultraviolet radiation -induced inflammatic and immunosup - pression［J］.The Journal of Investigative Dermatology，2004（2）：510-  517.

［11］Bone  R，Landrum  J，Mayne  S，et al.Twaroska macular pigment in donor eyes with and without AMD［J］.Invest Ophthalmol Vis Sci，2001 （42）：235-540.

［12］Curran Celentano J,Hammond B R,Jr,Ciulla T A,et al.Relation between dietary intake，serum concentrations，and retinal concentrations of lutein and zeaxanthin in adults in a midwest population［J］.Am J Clin Nutr，2001（74）：796-802.

[13] Li Jinsheng, Jin Ran, Chen Xia, et al. Research on the dose-effect relationship of the antioxidant effect of marigold lutein [J]. Chinese Journal of Traditional Chinese Medicine Information, 2013 (9): 26-27.

[14] Zhang  Z，Han  S，Wang   H，et  al.Lutein   extends  the  lifespan   of  Drosophila melanogaster［J］.Archives of Gerontology and Geriatrics， 2014（1）：153-159.

[15] Sheng Aiwu, Chen Cuiyun, Xie Yingyi, et al. Preliminary study on the extraction method and properties of marigold pigments [J]. Journal of Zhongkai University of Agriculture and Engineering, 2001 (4): 38-41.

[16] Li Dajing, Liu Chunquan, Fang Guizhen. Study on the extraction of lutein from marigold using enzyme as medium and organic solvent [J]. Transactions of the Chinese Society of Agricultural Engineering, 2007 (5): 232-236.

[17] Li Xiuxia, Han Lujia. Optimization of the ultrasonic extraction process of lutein from corn protein powder [J]. Transactions of the Chinese Society of Agricultural Engineering, 2008 (5): 81-85.

[18] Li Man, Wang Xianqing, Liang Ying. Study on the extraction process of lutein esters from marigolds [J]. Journal of Heilongjiang Bayi University of Agriculture and Forestry [J]. 2014 (4): 50-56.

[19] Li Dajing, Fang Guizhen, Liu Chunquan. Study on the extraction of lutein from marigold by ultrasonic-enhanced organic solvent extraction [J]. Forest Chemical Industry, 2006 (3): 128-130.

[20] Li Jianying, Deng Yu. Study on the extraction of lutein by microwave [J]. Food Industry Science and Technology, 2004 (8): 121-123.

［21］Ming Chang Chan，Shih Hsin，Duu Jong Lee，et al.Characterization， extraction and purification fo lutein produced by an indigenous microalga scenedesumsobliquus CNW-N［J］.Journal of Biochemical  Engineering，2012（78）：24-31.

[22] Tong Wanbing, Cao Longkui, Song Liang. Optimization of the process of extracting lutein from corn protein powder using supercritical CO2 by response surface methodology [J]. Food Science, 2013, 34 (4): 37-41.

[23] Li Yu, Wang Chengfu, Gao Yongxu. Development of xylitol lutein solid beverage [J]. Light Industry Science and Technology, 2013 (10): 15-16.

[24] Huang Yuanying. The health benefits of bilberry lutein soft capsules for relieving visual fatigue [J]. Sichuan Journal of Physiological Sciences, 2013 (4): 164-166.