What Is the Use of Natural Lutein Powder in Aquafeed?

Natural xanthophyll is a large group of oxygenated carotenoids that are widely found in nature, mainly derived from plants and algae. Among them, the flowers of Tagetes erecta L. are rich in natural xanthophyll, and mature planting and processing techniques make it a high-quality raw material for extracting natural xanthophyll. Natural lutein derived from marigolds is a high-quality natural coloring agent for aquatic animals. It also has the nutritional value of improving the antioxidant capacity of aquatic animals and acting as a precursor to vitamins. It also has a certain effect on improving animal health and growth performance.

At present, there have been extensive studies at home and abroad. Lutein derived from marigolds is a natural plant extract that is not only safe and reliable, but also beneficial to human health. It is worth further developing and utilizing in aquafeed. Since 2013, the Ministry of Agriculture and Rural Affairs announced No. 2045, which expanded the scope of application of natural lutein (derived from marigolds) to aquatic animals, and its addition to aquatic feeds in China has become increasingly common. Natural lutein extracted from marigolds is safe and effective. Its main pigment component is similar to the carotenoid component in the bodies of many aquatic animals. Its addition to aquatic animal feed has played a key role in solving the body color problems of many aquatic animals. However, many industry insiders still have some uncertainties about the characteristics of natural lutein and its application in aquatic feeds. This article summarizes a large number of domestic and foreign research results to form a review, with the hope of providing a reference for related practitioners.

1 Introduction to natural lutein

Natural lutein refers to a large class of oxygenated carotenoids that are widely found in nature. They are reddish-orange or yellowish-orange in color and mainly derived from plants and algae. Representative components are lutein and zeaxanthin, and their structural formulas are shown in Figures 1 and 2. The natural lutein content in different plant bodies varies greatly. Among them, the natural lutein content in marigold flowers is much higher than that in ordinary plants. It can be cultivated on a large scale, and the extraction and processing technology is mature. At present, a complete industrial chain has been formed, and it is a high-quality raw material for the production of natural lutein. Natural lutein extracted from marigolds is safe and effective, and has been widely used in food, medicine, feed and other fields.

Natural lutein has important physiological functions in humans and animals. Studies have shown that the macula region of the retina is rich in carotenoids, mainly lutein and zeaxanthin, which play a vital role in protecting the eyes. The mechanism is to filter out blue light, which has phototoxic effects, and quench singlet oxygen. Natural lutein is an effective substance for scavenging oxygen free radicals, which can reduce oxidative damage to cells caused by toxic substances, and thus has significant biological activity in controlling cancer, cardiovascular disease and enhancing the body's immune system.

2 Safety of natural lutein

Most of the natural lutein raw materials currently produced and used on the market come from marigolds. Marigold is an ancient traditional flower native to Mexico. It is often cultivated as an ornamental flower and is also an important medicinal plant. Its petals have the effect of clearing away heat and detoxifying the body.

As a product for food and health product use, the safety of natural lutein has been evaluated and approved by domestic and foreign authorities such as the US Food and Drug Administration (FDA), and it was approved for use as a food supplement in food and beverages in 1995. Hu Xian et al. [1] showed that the acute oral median lethal dose (LD50) of lutein for mice and rats is >10,000 mg·kg-1. The results of the Ames test, micronucleus test in mouse bone marrow polychromatic erythrocytes, and mouse sperm deformity test were all negative. It is believed that lutein is a non-toxic substance that can be developed and used as a food additive and health food ingredient. In fact, natural lutein has many health benefits and is already widely used in foods and health products. For example, many high-end infant formulas contain natural lutein, and there are a wide range of chewable tablets, capsules, and lozenges on the market with natural lutein as the active ingredient.

Wang Lubo et al. [2] conducted a systematic evaluation at the National Aquatic Feed Safety Evaluation Base to determine the safety of natural lutein added to aquatic animal feed. Natural lutein extracted from marigolds was added to the feed of yellow catfish at a dosage of up to 1,700 mg·kg-1 (this dosage is 10 times the possible intake dose for yellow catfish). The results showed that the yellow croaker had no adverse reactions at this dose, and on the contrary, there was a significant improvement in growth performance indicators compared to the control group. Liu Haiyan et al. [3] evaluated the safety of natural lutein additives for Chinese softshell turtles. The test results showed that the oral LD50 of a natural lutein feed additive with a lutein content of 4% by weight was >18,831 mg·kg-1, which is practically non-toxic. The results of the above test studies show that natural lutein is safe and reliable for aquatic animals.

3. The application value of natural lutein in aquatic feeds

3.1. Overview of the application of natural lutein

Animals cannot synthesize lutein themselves. Adding natural lutein extracted from marigolds to feeds has a long history of improving the quality of animal products and production performance both domestically and abroad, and has been widely used in Europe for many years [4]. In the early days, China only allowed the addition of natural lutein to poultry feed. Later, Guangzhou Lydall Biotechnology Co., Ltd. commissioned the national aquatic feed safety evaluation agency to conduct research on the safety and efficacy of natural lutein in aquatic animals. After the expert review by the Ministry of Agriculture and Rural Affairs, the scope of application of natural lutein (derived from marigolds) was expanded to aquatic animals in the Feed Additive Catalogue (2013).

3.2 The effect of natural lutein on improving the body color of aquatic animals

In the wild, aquatic animals mainly feed on natural lutein-rich natural baits such as plankton, small fish and shrimp, which are deposited in their bodies through the food chain, giving the animals a beautiful, vibrant natural healthy color. Under high-density intensive farming conditions, the main food source for aquatic animals is artificial compound feed, and the availability of natural baits is extremely limited. However, the raw materials for conventional artificial compound feeds have low lutein content, and a large amount of it is also lost during storage and processing. For artificially farmed aquatic animals that are highly dependent on compound feeds, if natural lutein is not added, the final aquatic animals will be pale in color and it will be difficult to achieve the natural color that consumers demand.

The main pigment component of natural lutein is similar to the carotenoid component in the bodies of many aquatic animals. When added to animal feed, it is easily absorbed, deposited and utilized by aquatic animals, and the coloring effect is natural and beautiful, similar to that of aquatic animals in the wild. Leng Xiangjun et al. [5] concluded that adding 100 mg·kg-1 of natural lutein to the feed can effectively improve the body color of farmed mandarin fish, making it similar to the body color of wild mandarin fish.

Wu Huachang et al. [6] showed that lutein extracted from marigolds can effectively color yellow catfish, and the body color of the test group supplemented with lutein is basically the same as that of wild yellow catfish. Hu B. et al. [7-8] found through multiple studies that natural lutein has a good coloring effect on American catfish, and achieved satisfactory test results. B. Yuangsoi et al. [9] found that lutein can effectively increase the redness of the skin and the pigment content of koi carp when coloring koi carp. Liu X. D. et al. [10] found that natural lutein has a significant coloring effect on rainbow fish, especially on the dorsal fin, which is better than astaxanthin. Wang P. et al. [11] found that the content of carotenoids in the liver and carapace of the Chinese soft-shelled turtle was found to be linearly related to the amount of natural lutein added to the feed, and the yellowing of its carapace and pectoral skin was also proportional to the amount of natural lutein added to the feed, indicating that the addition of natural lutein to the feed has a good deposition effect in the Chinese soft-shelled turtle. In addition, there are also many other reports on the use of natural lutein in yellow or red-colored species such as yellow croaker, red sea bream, and ornamental fish. The research results all show a good coloring effect [12-19].

When natural lutein is added to shrimp and crab feed, some of it can be converted into astaxanthin, effectively improving the body color of shrimp and crab. E. J. Vernon-Carter et al. [20] found that natural lutein has a good coloring effect on vannamei shrimp, and speculated that its main components, lutein and zeaxanthin, can be metabolized by shrimp into astaxanthin and deposited in the body. M. Gocer et al. [21] found that red peppers and marigolds can significantly increase the carotenoid content of short-gutted shrimp. E. Aguirre-Hinojosa et al. [22] found that marigold extract natural lutein is effective in improving the body color of Penaeus vannamei. The astaxanthin content of the carapace and muscles of the experimental group was significantly higher than that of the control group. K. Mondal et al. [23] found that feeding Penaeus monodon with spirulina enriched with natural lutein can significantly increase the astaxanthin content of P. monodon muscle tissue.

However, some aquatic animals have a certain degree of selectivity in the absorption and utilization of pigments, which requires attention in practical applications. According to R. E. Olsen et al. [24], when the astaxanthin:lutein ratio in the test feed was 2.5:1, the ratio in the muscle and plasma of Atlantic salmon at the end of the experiment reached 25:1, indicating that the absorption and utilization of astaxanthin by Atlantic salmon was much higher than that of lutein.

3.3 The effect of natural lutein on improving the antioxidant capacity of aquatic animals

Like many plant extracts, natural lutein has the effect of improving the body's resistance to oxidation. Adding it to aquatic animal feed can improve the antioxidant indicators of some aquatic animals. Guan Xian Tao's[25] research confirmed that natural lutein can improve the antioxidant-related indicators of the liver of the Eastern star grouper, such as superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), total antioxidant capacity (T-AOC), and malondialdehyde (MDA). Han Xingxing et al. [18] found that adding a mixture of lutein and astaxanthin (1:1) to the feed can improve the body color of adult yellow croaker and enhance its antioxidant capacity. Liu Cui et al. [26] showed that the blood SOD activity of yellow croaker fed with natural lutein was significantly higher than that of the control group.

3.4 Nutritional value of natural lutein for aquatic animals

The nutritional value of natural lutein for aquatic animals is often overlooked, but studies have shown that natural lutein has a certain role as a vitamin A precursor for aquatic animals, especially freshwater fish. J. Gross et al. [27] confirmed the role of natural lutein as a vitamin A precursor in their study of two freshwater fish species, guppies and swordtails. A. B. Barua [28] showed in his study of the Indian freshwater catfish that the fish can convert lutein, the most common component of natural lutein, into dehydroepi-retinol (VA2), but β-carotene and zeaxanthin cannot be converted.

3.5 The effect of natural lutein on improving the growth performance of aquatic animals

Natural lutein also has a certain effect on improving the growth performance of animals. A study by Yang Wenping et al. [29] showed that natural lutein products have a positive effect on improving the growth performance of yellow catfish, and can help to improve survival rates and growth rates. Further research found that adding 0.4% to 0.8% of natural lutein products to the feed can improve the activity of trypsin, amylase and lipase in the stomach, intestines, liver and pancreas of yellow catfish to varying degrees.

Wang Lubo et al. [2] found that the addition of natural lutein to the feed can significantly improve the growth performance of yellow catfish. Feeding yellow catfish with a feed containing 118 mg·kg-1 natural lutein increased the specific growth rate (SGR) by 0.19 compared to the control group, reduced the feed coefficient by 0.5, and improved the protein and energy deposition rate also improved. It is speculated that natural lutein can significantly stimulate the activity of certain gastrointestinal digestive enzymes in yellow catfish, thereby improving the utilization rate of feed and the digestibility of nutrients, and ultimately exhibiting a growth-promoting effect. K. P. Besen et al. [19] found that the main component of natural lutein, lutein, not only has a good coloring effect on goldfish, but also increased the survival rate of the fish. Wang P. et al. [11] found that adding 80 mg·kg-1 natural lutein to the feed of Chinese soft-shelled turtles significantly improved growth performance, feed conversion rate and amino acid content of muscle tissue.

4 Precautions for the use of natural lutein

The coloring of aquatic animals is a systematic project closely related to the animals themselves and feed formulation technology, while the regulation and management of pigment cells is a key element.

Pigment cells in aquatic animals include melanocytes, red pigment cells, yellow pigment cells and iridescent cells. Natural xanthophylls are mainly deposited in red pigment cells and yellow pigment cells, and a small amount is also deposited in fat and muscle. The development, differentiation and regulation of pigment cells are affected by multiple factors. Therefore, the deposition of pigments in aquatic animals is not simply a matter of adding pigments. More importantly, the characteristics of the cultured species and the management of pigment cells need to be fully considered. The way in which different pigments are deposited, the deposition sites and the deposition efficiency of different aquatic animals at different stages are all different, and more attention must be paid when applying them.

The deposition effect of natural lutein can be seriously affected by feed formulation, processing and storage techniques. Common toxic substances in feed, such as oxidized lipids, mycotoxins, non-protein nitrogen and histamine, can cause damage to fish organs, metabolic disorders and affect the growth and development of pigment cells, which can hinder the absorption, transport and deposition of pigments, ultimately leading to abnormal body coloration. The levels of added oil, vitamins (especially vitamin A and vitamin E), and antioxidants in the feed can also affect the transport, deposition, and stability of natural xanthophylls. In addition, since natural carotenoids are sensitive to light, heat, and oxygen, attention needs to be paid to losses caused by processing and storage.

Since the deposition of natural xanthophylls mainly depends on the growth and development of pigment cells, and the growth and development of pigment cells needs to go through a physiological development process, it takes a certain amount of time for natural xanthophylls to be stably deposited in the body, and they cannot be deposited indefinitely. There is a phenomenon of “saturation”. Wang Lubo et al. [2] found that the amount of natural xanthophyll added to yellow croaker to achieve a 90-day saturation of yellow color was 118 mg·kg-1 feed. Analysis of the natural coloring mechanism and practical application experience shows that a small amount of natural xanthophyll added over a long period of time is conducive to achieving a better and more stable deposition effect.

5 Summary

In the past 30 years, the global capture production of aquatic products has shown a negative growth trend, while aquaculture has grown rapidly year by year, and the aquaculture industry has made a huge contribution to solving human food security. After the problem of satiety has been solved, people have higher requirements for the “color, flavor and fragrance” of food, and the natural and healthy body color of aquatic animals is an important factor influencing consumers' purchase decisions. Compared to wild aquatic animals, farmed aquatic animals are prone to poor body color. Natural lutein extracted from marigolds, the main pigment component of which is similar to the carotenoid component in many aquatic animals, plays a key role in solving the body color problem of many aquatic animals when added to the feed of aquatic animals. Natural lutein also has the effect of improving the antioxidant capacity of aquatic animals, and has nutritional value as a precursor of vitamins. It also has a certain effect on improving animal health and growth performance. As a purely natural plant extract, it is not only safe and reliable, but also beneficial to human health, and is worth further in-depth development and utilization in aquatic feeds.

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