What Is the Coloring Use of Lutein Powder?

Since entering the 21st century, people's living standards have improved significantly, and consumption habits have undergone fundamental changes along with the enrichment of material life. “Healthy, green, organic, and ecological” have become hot topics of discussion. Regarding the quality of aquatic products, people not only pursue delicious meat, but also demand that the color of aquatic products be close to natural. China has vast waters and a wide variety of aquatic animals, including many with bright colors, such as fish, shrimp and crabs. such as Pelteobagrus fulvidraco, Pelodiscus sinensis, Pseudosciaena crocea, Oncorhynchus mykiss, Brocarded carp, etc.

With the development of intensive artificial breeding, the scale of breeding these economically valuable fish has expanded, The breeding cycle is shortened. After being fed large amounts of artificial compound feed, the color of the fish often becomes lighter or abnormal, for example, the yellow catfish becomes “banana fish” and the Chinese soft-shelled turtle “turns white”. This phenomenon will greatly reduce the commercial value of aquatic products. In recent years, many scientific researchers and feed-related companies have devoted a great deal of energy to studying the coloring of aquatic animals. This article reviews the coloring principle of natural xanthophyll, which is widely used in yellow-colored aquatic animals, and its new application progress in aquatic animals, in order to help improve the theoretical level of xanthophyll research and production practices.

1. Chemical properties and functions of natural xanthophyll

Natural xanthophyll is a carotenoid widely found in vegetables, flowers and algae. Plants and microorganisms can synthesize xanthophyll themselves, while humans and animals can only obtain it from food. In the 1990s, scholars initially discovered that xanthophyll is an antioxidant in the body. and it was subsequently reported that lutein has physiological functions such as antioxidant, anti-tumor, and prevention of cardiovascular and cerebrovascular diseases, as well as the ability to enhance humoral immune response, stimulate lymphocyte proliferation, protect the skin, and prevent age-related macular degeneration. Lutein has physiological effects that other carotenoids do not have, and research on lutein has sparked a craze.

Lutein contains the elements C, H, and O, and has the molecular formula C40H56O2. It is a long chain with 40 carbon atoms and many conjugated double bonds, with a hydroxyl group at the end of the chain. This unique chemical structure not only gives lutein its bright color, but also gives it specific physical and chemical properties. Its hydrophobic long chain is buried in the phospholipid molecular layer of the cell membrane, and its hydrophilic hydroxyl group is present on both sides of the membrane, binding to the lipids of the cell membrane to the greatest extent. At the same time, studies have shown that lutein, as a monomer, is extremely unstable to heat, while its hydroxyl group is more stable to heat after esterification with fatty acids.

2 Extraction and analysis methods for natural lutein

The main methods of lutein extraction include organic solvent extraction, membrane separation technology, microwave heating and extraction. Lutein extracted from marigolds is mainly extracted using an extraction method. After fermentation, drying, granulation, hexane extraction and negative pressure evaporation, lutein resin is obtained. There is also a carbon dioxide extraction method.

3 The basis of coloring in aquatic animals and the mechanism of lutein absorption

The basis of the formation of the body color of aquatic animals is the type, quantity and distribution of pigment cells in the skin scales, as well as the corresponding content and position of pigment particles. There are four main types of pigment cells in bony fish: melanocytes, xanthocytes, erythrocytes and iridocytes. Melanocytes are divided into two types: epidermal melanocytes and dermal melanocytes. They contain melanin granules and appear black or brown under certain wavelengths of light. The chromophores of yellow and red pigment cells are carotenoids and porphyrins. Carotenoids cannot be synthesized in fish and must be obtained from food, while porphyrins can be synthesized.

The color changes in aquatic animals can be divided into morphological and physiological changes. Morphological and physiological changes mainly refer to the changes in the number of pigment cells in the epidermis and the migration of their position. For example, the patterned color on the surface of the yellow catfish is the result of the combined expression of pigments such as melanin and carotenoids. Melanin can be synthesized in the yellow catfish. Melanin is produced by the action of tyrosinease on tyrosine to form dopamine, which is then produced through a series of reactions. The shade of yellow is directly related to the total carotene and lutein content. Physiological body color changes mainly involve the aggregation and diffusion of pigment particles in the pigment cells of the dermis, as well as the regulation of nerves and hormones.

The metabolic pathway of pigments in animals has always been a difficult problem to study. So far, only Hate et al. have proposed a metabolic pathway hypothesis for the synthesis of astaxanthin from zeaxanthin: zeaxanthin β-carotene-3-ol → 4-oxozeaxanthin → astaxanthin. Natural lutein is easily soluble in fats and fat-soluble solvents. It needs to be absorbed and metabolized with the help of fats in food. It is therefore speculated that the absorption of lutein is similar to that of fat-soluble substances and occurs in the small intestine.

Wang Lubo et al. (2012) speculate that the absorption process of natural lutein from marigolds is as follows: in the chyme, lutein is accompanied by fat being emulsified into milk droplets, which are further digested by lipase and bile. Lutein is finally solubilized in mixed colloidal particles and absorbed by intestinal epithelial cells. Some of the absorbed lutein is secreted into the lymphatic system in the form of chylomicrons and enters the blood circulation. The chylomicrons are then degraded by lipoprotein lipase, and the lutein in the chylomicron residue is absorbed by the liver. The lutein absorbed by the liver is either stored in the liver or resecreted into very low-density lipoproteins and enters the blood circulation, where it is delivered to low-density lipoproteins. and finally, lutein is absorbed into tissues through lipoprotein receptors, but there is no other relevant data to verify this.

4 Research progress on lutein in special aquatic animals

4.1 Lutein addition levels in aquatic animals

Wu Huachang et al. (2005) compared the body color and skin color of wild and cultured yellow croakers (Pseudosciaena crocea) and the lutein content of their muscles by adding feed with different lutein levels. It was found that lutein extracted from marigolds can effectively color yellow croakers, and the optimal lutein addition level is 100 mg/kg. Shi Xiangyi et al. (2010) showed that adding 200 mg/kg lutein to the feed of hybrid catfish can effectively improve its body color. Leng Xiangjun et al. (2003) investigated the effect of adding lutein to the feed on the body color of the local bearded catfish, concluded that adding lutein products to the feed can effectively improve the body color of cultured mandarin catfish adults and fry, and the appropriate additive amounts are 100 mg/kg feed or 50 mg/kg feed, respectively. The effective additive amount in goldfish feed is 150 mg/kg lutein. When lutein is used to color fish, it should be added in the right amount for fish of different species, body colors, and pigment metabolism types.

Wang Lubo et al. (2014) studied the effect of the addition level of natural lutein (derived from marigolds, with a content of 4.64%) on the growth and skin coloration of yellow catfish. The results showed that 4.2~1 700 mg/kg of natural lutein significantly improved the growth performance of yellow catfish with an initial body weight of 21 g. The optimal dosage of natural lutein as a skin colorant for yellow catfish was 76.25 mg/kg feed. The coloring function of lutein is a gradual and cumulative process. The above research results show that the addition rate of lutein in feeds for different aquatic animals is different, and the addition amount is also different at different stages of the same animal's growth. In addition to the amount of additive, the coloring time is also a factor that must be considered during feed production and application.

4.2 Factors affecting the coloring effect of lutein in aquatic animals

The coloring process of lutein in aquatic animals is very complex, and is affected by both endogenous factors (heredity, physiological status of the animal, and regulation of the neuroendocrine system) and exogenous factors (type of pigment source in the feed, feed quality, feeding level, feeding time, etc.).

Fundamentally, the body color of aquatic animals is controlled by genetic factors. Different species of fish have different body shapes and colors, which is the result of long-term adaptation in nature. At the same time, fat, which is the main medium for the absorption and transport of pigments, has a significant effect on changes in fish color. An appropriate high fat content is conducive to the absorption and utilization of pigments in the feed. However, attention should be paid to the type and quality of fat. Oxidized fat does more harm than good to the absorption of pigments, which can cause problems with the deposition of melanin and lead to the lightening of the body color of aquatic animals or the appearance of “banana fish” in silver carp.

A higher content of fat-soluble vitamins A and E in the feed helps to enhance the coloring effect, mainly because the strong antioxidant properties of vitamins help to protect the lutein in the feed. Certain drugs such as sulfonamides and aflatoxin can have a certain side effect on the coloring function of lutein. At the same time, the transport of lutein in the blood depends on lipoproteins, and calcium has a greater affinity for lipoproteins than lutein. Therefore, a high calcium content will cause competitive inhibition of lutein absorption, reducing the coloring effect.

Xu Xia's (2005) research shows that lutein extracted from marigolds is relatively stable in slightly acidic, neutral and alkaline solutions. Lutein is relatively stable to heat, reducing agents and oxidants, but is sensitive to sunlight and should be stored away from light. Preservatives have basically no effect on the stability of lutein at low concentrations, but at high concentrations can reduce the stability of lutein. Citric acid and malic acid have a certain protective effect on lutein. Lutein is relatively tolerant of the metal ion Fe3+ and can be used together with these additives. Na+, Mg2+, Mn2+, Ca2+ and Fe2+ reduce the stability of the pigment, so contact with these ions should be avoided during production and use. Vitamin C has a clear protective effect on lutein in sunlight. In addition, aquatic animals are in a complex culture water body, and the conditions of the culture water body itself (such as water temperature), the breeding management of the breeder, and the light in the culture can also affect the deposition of pigments. When the body color of farmed animals is abnormal, a judgment should not be made lightly based on a single situation.

4.3 Effect of feed processing technology on lutein application

Lutein is very susceptible to light, stress, etc. Currently, feed is processed using extrusion to produce pellets or puffed to produce puffed pellet feed. Different feed processing technologies have different effects on the application of lutein in aquafeed. Shi Shaoyi et al. (2010) added 200 mg/kg lutein to the basic feed and used an extruder and a meat grinder to granulate the lutein-added feed. The two forms of granulation had no significant effect on the coloring effect.

Wang Lubo et al. (2012) used natural lutein derived from marigolds as the test subject and respectively, adding 0, 0.15%, 0.3%, 0.6%, and 8% to the basic feed. The theoretical values of lutein were 0, 69.6, 139.2, 278.4, and 3,700 mg/kg, respectively. After the raw materials were crushed and thoroughly mixed, they were extruded under the following process parameters: feed zone: 90°C for 5 s, kneading zone: 130°C for 3 seconds, maturing zone: 60°C for 4 seconds, under the process parameters of extrusion and puffing to make 2 mm puffed sinking granules. The extrusion process has an average loss rate of 43.40% for natural lutein.

4.4 Effect of lutein addition on special aquatic animals

Adding lutein to special aquatic animal feed not only has a good coloring effect, but as research progresses, lutein may also be shown to promote growth, improve the activity of digestive enzymes and to a certain extent reduce fat accumulation. Yang Wenping et al. (2008) showed that adding lutein (a natural extract, the main component of which is a carotenoid, of which the lutein content is ≥1.5% and zeaxanthin ≥ 35.0%) can help to improve the growth rate and survival rate of yellow catfish. An addition level of 0.8% can significantly increase the protease activity, amylase activity and lipase activity of yellow catfish.

Ding Xiaofeng et al. (2006) showed that adding canthaxanthin (a synthetic carotenoid, with 10% of the active ingredient being canthaxanthin), flavoxanthin and marigold yellow (both flavoxanthin and marigold yellow are marigold extracts, rich in lutein and zeaxanthin, with 2% of the active ingredient) had a certain effect on the fat content in the liver and pancreas of the fish. The fat content in the liver and pancreas of the fish in the flavoxanthin group decreased significantly by 18.2% compared to the control group. In Yang Wenping et al. (2010), the addition of 0.8% gold and safflower yellow to the feed also significantly reduced the feed conversion ratio (P<0.05), and the weight gain rate of the gold and safflower yellow group was higher than that of the control group.

4.5 Lutein toxicity study

Natural lutein additives used in feed are of low purity and often exist in the form of lutein esters in feed. Carriers are used for adsorption, and the carriers often contain some chemical substances and other impurities. Whether they will have a negative impact on aquatic animals is an urgent problem that needs to be solved when lutein additives are used in aquatic animal feed. So far, studies have reported that the addition of lutein additives to feed at certain doses can improve the body color of poultry and fish without causing adverse effects. At the same time, Liu Haiyan (2012) and others have evaluated the safety of natural lutein additives for soft-shelled turtles. Toxicity experiments of natural lutein additives were conducted using single and continuous oral administration of lutein additives, The results showed that the oral LD50 of the natural lutein additive (containing 4% lutein) was >18,831 [mg/(kgbw)], which is practically non-toxic; the maximum no-observed-adverse-effect dose for the Chinese soft-shelled turtle for 21 days.

Wang Lubo et al. (2012) found that natural lutein extracted from marigolds is safe for reasonable use in aquatic animals. Hu Xian et al. (2009) conducted tests in accordance with the Ministry of Health's “Procedures for Toxicological Evaluation of Food Safety and Inspection Methods” using acute toxicity tests, micronucleus tests in mouse bone marrow polychromatic erythrocytes, and mouse sperm deformity tests. The study showed that lutein is non-toxic and can be developed and used as a food additive and health food ingredient. These studies generally show that natural lutein is safe as a feed additive, but whether there are any other toxic side effects that have not been studied needs to be further investigated.

5 Conclusion

Natural lutein is a good colorant for aquatic animals and has broad prospects in the field of aquatic feed. There are many factors that affect its coloration, and its metabolic mechanism and the relationship with other factors are still difficult problems for us to study.

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