Is Astaxanthin in Salmon Safe?

3. Natural Systems as a Source of Astaxanthin

Astaxanthin is obtained from primary sources such as higher plants; microscopic phytoplankton algae Haematococcus pluvialis [2], Chlorella zofingiensis, Chlorococcum sp. [66]; and some microorganisms, i.e., Xanthophyllomyces dendrorhous (anamorph Phaffia rhodozyma) yeasts and bacteria such as Mycobacterium lacticola, Brevibacterium, Agrobacterium aurantiacum, Alcaligens sp. strain PC-1. and Paracoccus carotinifaciens [10,67]. The industrial production of natural astaxanthin started in the 1980s. Cynotech Corporation (Kona, HI, USA) is the oldest and largest producer of the pigment from microalgae. The trade name of the product is BioAstin®. It is oleoresin extracted from Haematococcus pluvialis. It includes a minimum of 4 milligrams of astaxanthin per gel cap. In China, astaxanthin in industrial production is extracted from krill and crustacean byproducts.

Species of the Adonis genus, i.e., A. aestivalis and A. annua (Figure 3a), are the richest sources of astaxanthin. According to Cunningham and Gantt [68], this pigment makes up about 1% of the dry matter of petals of these plants.

Natural sources of astaxanthin; (a) Adonis plants, (b) photo of H. pluvialis alge, (c) was adapted from [69].

However, due to the low yield of flower biomass from the cultivation area, this plant is not a cost-effective source of the pigment. Early studies on using Adonis species as industrial sources of astaxanthin concerned the obtaining of cultivars with a larger number of petals in the flower head [70]. Later studies concerned the isolation of genes encoding the astaxanthin biosynthesis pathway from Adonis plants and their transfer to other plants, e.g., marigolds, which guaranteed a high yield of biomass with carotenoids [71]. As the synthesis of carotenoids depends on the content of precursors and the possibility of converting them in the conversion pathway, researchers became particularly interested in plants that can produce large amounts of β-carotene, such as marigolds, various oil palm species, canola rapeseed, sweet potatoes and maize because it is possible to insert DNA fragments responsible for the conversion of β-carotene into astaxanthin from Adonis plants into the genome of these plants [72,73]. Typically, the biosynthesis of astaxanthin from β-carotene requires ketolase and hydroxylase to add carbonyl and hydroxyl at positions 4 and 3 of each terminal β-ionone ring, respectively. Researchers successfully produced transgenic tomatoes with a high concentration of free astaxanthin in leaves (3.12 mg/g) and its esterified form in fruit (16.1 mg/g). The success was achieved through co-expression of two genes from microalgae, i.e., β-carotene ketolase from Chlamydomonas reinhardtii and β-carotene hydroxylase from Haematoccocus pluvialis [74]. There are also studies on genetic modification of marigolds (Tagetes) and their use as a source of astaxanthin for feeding animals [75].

At present, microbiological synthesis of astaxanthin is one of the most intensely developing research areas. It has more advantages than plant production. It is easy to culture microorganisms, which grow fast on cheap culture media. Their development does not depend on weather conditions, and the shade of the pigment is stable [76]. However, the use of microbial systems for astaxanthin production is not very economical. The pigment is an intracellular metabolite. Therefore, the cost of biosynthesis depends on the cost of biomass production, the concentration of the pigment in cells, the metabolic activity of the cells producing the pigment and the need to isolate the pigment from the cells and purify it [53].

Haematoccocus pluvialis freshwater microalgae are a basic source of natural astaxanthin on the market. They accumulate up to 4% of the pigment in dry biomass. It is the highest natural concentration of astaxanthin. The predominant form of astaxanthin in H. pluvialis is monoester [2]. Researchers stress the fact that it is particularly difficult to breed microalgae in open systems, e.g., in ponds, due to the risk of contamination with unwanted species of algae, bacteria, fungi, etc. For this reason, it is necessary to use expensive, high-capacity photobioreactors [77]. Another problem is that Haematoccocus pluvialis grow slowly, and their yield of biomass is low when they are grown on traditional media. Apart from that, they accumulate astaxanthin only when they are exposed to environmental stress, i.e., a nitrogen or phosphorus deficit, the presence of salicylic acid and ethanol, high salinity of the growth medium or intensive light [2,78,79]. In such cases, they form immotile thick-walled hematocysts that contain the pigment (Figure 3b). Thirdly, in order to isolate astaxanthin from hematocysts, it is necessary to disintegrate the thick cell wall. All these procedures make astaxanthin very expensive. Its production is limited to specialized markets, chiefly the pharmaceutical market. Astaxanthin is produced from Haematoccocus pluvialis microalgae in the United States, Japan and India [80]. It is a component of vitamin preparations, dietary supplements and protective creams. It is also used in organic farming. In 2014, the EFSA Panel on Dietetic Products, Nutrition and Allergies of the European Commission issued a positive opinion about the safety of astaxanthin-rich ingredients of AstaREAL preparations made from Haematoccocus pluvialis. According to the opinion, their consumption was not considered to be nutritionally disadvantageous and there were no safety concerns regarding genotoxicity [36]. In December 2017, astaxanthin-rich oleoresin from Haematococcus pluvialis algae was on the European Commission list of novel foods [81]. H. pluvialis cultivation can be carried out both in closed systems exposed to the sunlight or strictly controlled lighting, or in open ponds. Supercritical fluid extraction (SFE) is used to remove astaxanthin oleoresin from dried algal cells with supercritical CO2 or ethyl acetate as solvents The technique for SFE is described below. The astaxanthin is diluted in edible oils such as olive oil, safflower oil, sunflower oil or MCT (Medium Chain Triglycerides) at six levels: 2.5%, 5.0%, 7.0%, 10.0%, 15.0% and 20.0%. These preparations are intended to be used in fermented and non-fermented liquid dairy products, fermented soya products and fruit drinks for healthy adults [36].

For many years, scientific researchers and industrial producers have been particularly interested in red Xanthophyllomyces dendrorhous yeasts (Figure 3c), which synthesize unesterified astaxanthin, predominantly in the (3R, 3R′) form, which is different from that of Haematoccocus pluvialis algae. It is concentrated with other carotenoids in lipid droplets suspended in the cytoplasm or in cytoplasmic membranes in the lipid layer (it is not visible in microscopic studies). This form is very stable [82].

Studies indicated that unesterified astaxanthin was more efficiently taken up and utilized for pigmentation in rainbow trout than astaxanthin dipalmitates, probably due to the limited capacity of intestinal esterases to hydrolyze these esters [83]. It is particularly important because inactivated yeast biomass can be a ready product, which is not only rich in assimilable astaxanthin, but also necessary nutrients—proteins, lipids and B vitamins [11].

Low cellular concentration of astaxanthin is an essential problem while using Xanthophyllomyces dendrorhous yeasts for industrial production of the pigment. The content of astaxanthin in wild strains ranges from 0.01 to 0.03% of dry matter. As the cellular concentration of the pigment is so low, it is necessary to add a few percent of yeast to feeds so as to give the right color to salmon or trout meat. However, it is not advisable in aquaculture due to the high content of polysaccharides in the yeast cell walls [84]. Only the Xanthophyllomyces dendrorhous strains capable of astaxanthin synthesis 5- to 10-fold higher than in wild strains may be used for industrial production of the pigment and greatly reduce its market price [82,85]. Such strains can be obtained with chemical mutagenesis [86] or with a combination of classical mutagenesis and genetic pathway engineering [87,88].

Inedible parts of shrimp, crabs and other crustaceans, i.e., heads, shells, tails, etc., can be used as sources of natural astaxanthin in aquaculture. According to Mezzomo et al. [89], the annual worldwide capture of marine crustaceans was 3.2 million tons. Inedible byproducts made up 40–56% of the raw material weight, depending on the species, size and shelling procedure [90,91]. Non-polar solvents and vegetable oil are routinely used for industrial extraction of carotenoids, including astaxanthin, from crustacean byproducts. The choice of solvent is very important because it affects the astaxanthin extract quality. The solvent must be non-flammable, non-toxic, non-volatile and effective at low temperatures. Sunflower, groundnut, coconut and rice bran oils seem to be the most adequate. In recent years, flaxseed oil has gained considerable attention as a potential astaxanthin extractant due to the high content of omega-3 acids, i.e., alpha-linolenic acid and linoleic acid [92]. These acids have been shown to provide protection against cardiovascular disease and inflammation. Dispersed natural astaxanthin in flaxseed oil may provide healthier food options for consumers. Pu et al. [91] indicated that astaxanthin extracted from shrimp byproducts by means of flaxseed oil effectively protected the fatty acids it contained from oxidation during heating from 40 to 60 °C for 4 h. Nevertheless, the rate of astaxanthin degradation in flaxseed oil was significantly influenced by temperature. Astaxanthin was stable in flaxseed oil only at 30 and 40 °C but exhibited substantial degradation at 50 and 60 °C. In the near future, astaxanthin preparations in flaxseed oil may become as popular as krill oil (e.g., Gold Krill, Mega Red Omega 3, Krill Oil), which is a source of astaxanthin and omega-3 acids. These preparations are recommended to prevent atherosclerosis, cardiovascular, eye and neurodegenerative diseases caused by aging [91].

Higher efficiency of astaxanthin extraction from crustacean byproducts can be achieved by using organic solvents such as chlorinated ones. However, they are toxic and potentially carcinogenic. On the other hand, solvents used for industrial production such as n-hexane, n-heptane, acetone, methanol and petroleum ether require high temperatures, affecting thermolabile astaxanthin. Otherwise, the pigment extraction efficiency is low [90,93].

Supercritical fluid extraction (SFE) can be used as an alternative to conventional techniques of carotenoid extraction from crustacean byproducts. The use of nonpolar supercritical carbon dioxide (SC-CO2) as the solvent is the most commonly employed in SFE for extracting low-polarity and heat-sensitive bioactive compounds due to its low critical properties (Tc = 31.1 °C; Pc = 73.8 bar) [94]. SC-CO2 is chemically inactive, available, economical and non-toxic. It is not necessary to remove the solvent when CO2 is used in a supercritical state because this gas is at a normal temperature and atmospheric pressure. Apart from that, CO2 has GRAS status, and it is not expensive [89,90]. Currently, SC-CO2 is the most modern and effective method of obtaining essential oils, polyunsaturated oils, phytosterols, carotenoids, flavonoids and anthocyanins [95]. Sánchez-Camargo et al. [90] extracted astaxanthin from freeze-dried red spotted shrimp (Farfantepenaeus paulensis) waste (including the head, tail and shell) using SC-CO2 and evaluated the effects of the extraction conditions of pressure (200–400 bar) and temperature (40–60 °C) on the total extraction yield, astaxanthin extraction yield and astaxanthin concentration in the extract. It was shown that temperature, and especially pressure, had a significant effect on the astaxanthin extraction yield. The highest amount of the extract (with 39% astaxanthin recovery) was obtained at 43 °C and 370 bar. At low pressures, an increase in temperature resulted in a decrease in the amount of astaxanthin extracted.

Mezzomo et al. [89] studied SFE efficiency in order to concentrate carotenoids from pink shrimp (Penaeus brasiliensis and Penaeus paulensis) processing waste (composed essentially of head, carapace). The process efficiency was studied by the effects of the operational conditions and co-solvents, hexane:isopropanol solution (50:50, v/v) and sunflower oil (as co-solvents mixed to the supercritical CO2 in concentrations of 2 and 5% (w/w)). The highest astaxanthin yield was obtained with SC-CO2 at 300 bar and 60 °C. Although the use of hexane:isopropanol solution in SFE was successful to enhance the extraction yield compared to SFE with SC-CO2, the system selectivity did not increase carotenoid concentration. The authors of both studies indicated that carotenoid extraction increased along with CO2 density. The pigment extraction efficiency was lower at lower pressures and higher temperatures.

However, there are some limitations to the use of crustacean byproducts as a basic source of astaxanthin for aquaculture. Apart from the seasonal availability of crustacean byproducts (e.g., in Asian countries), the high costs of their storage and the need to protect them from decay (usually by mild lactic acid fermentation or with organic acids), these byproducts have a low content of astaxanthin—about 0.15%. Therefore, their content in feeds must be high (10–25%) to achieve adequate color of animal tissues. Unfortunately, they contain large amounts of water, ash and chitin, which limit their quantitative share in feed [2]. Additionally, even low concentrations of organic acids used for preservation cause the conversion of astaxanthin monoesters into diesters and reduce the amount of carotenoids recovered from byproducts. However, Sachindra et al. [96] indicated that lactic acid fermentation reduced the amount of solvent (organic compound or vegetable oil) used for the isolation of carotenoids from shrimp byproducts.

The Occurrence, Structure and Industrial Potential of Astaxanthin

In nature, astaxanthin can be found in aquatic environments. It gives pink and red colors to the meat of fish such as Atlantic salmon, rainbow trout, Arctic char and red bream and to the shells of crustaceans such as krill, shrimp and lobster, etc. as well as the feathers of some wading birds, e.g., flamingo, scarlet ibis [9,10]. In the natural environment, the color of these animals is the result of bioconcentration of the pigment at consecutive trophic levels in the food chain [11]. In the aquatic environment, astaxanthin can be found in algae, which can synthesize this pigment, as well as in plankton crustaceans, which are capable of astaxanthin conversion from carotenoid precursors (chiefly from β-carotene and zeaxanthin). Thus, the color intensity of animal tissues mostly depends on the presence of astaxanthin in these animals’ diets. This fact significantly influences the use of this pigment in the feed industry.

Like most carotenoids, astaxanthin is a 40-carbon tetraterpene consisting of linked isoprene units. The molecular structure of astaxanthin is composed of a linear polyene chain and two terminal β rings (Figure 1) [12]. The system of 11 conjugated double bonds determines the pink and red color of astaxanthin (absorption maximum: in dimethyl sulfoxide (DMSO)—492 nm, in acetone—477 nm, in methanol—477 nm, in dimethylformamide—486 nm, in chloroform—86 nm) and is responsible for its anti-oxidative potential [13]. Apart from that, both terminal rings of astaxanthin contain two polar function groups: hydroxyl (OH) located at the two asymmetric carbons C3 and C3′ and keto (=O) at carbons C4 (Figure 1).

Configurational stereoisomers of astaxanthin.

The presence of these groups is typical of astaxanthin and makes it unique among other carotenoids. Thanks to the polar–non-polar structure, astaxanthin can fit the hydrophobic polyene carbon chain inside the bilayer lipid cell membrane, and its polar terminal rings can be located near its surface (Figure 2). In consequence, in comparison with other carotenoids, astaxanthin exhibits very high anti-oxidative activity in lipid systems [14].

The location of astaxanthin and other antioxidants in the cell membrane (adapted from [15]).

Astaxanthin was found to protect membrane phospholipids and other lipids from peroxidation more effectively than β-carotene and lutein [16,17]. Its anti-oxidative activity is 10 and 100 times higher than that of β-carotene and vitamin E, respectively [18,19]. The outstanding anti-oxidative potential of astaxanthin has encouraged numerous investigations which indicated its potential clinical use in the prevention and treatment of diseases associated with reactive oxygen species such as cancers [20,21], neurodegenerative diseases [22,23,24], eye diseases (cataract, macular degeneration, asthenopia) [25,26], atherosclerosis and type 2 diabetes [15,27,28,29]. Astaxanthin counteracts gastric inflammations caused by Helicobacter pylori (chronic type B gastritis, peptic ulcer disease and gastric carcinoma) [30] and inflammations of the vocal folds [31]. It might be used to treat clinical sepsis [32]. It exhibits an immunomodulatory effect [33,34]. In contrast to β-carotene, astaxanthin easily permeates the blood–brain barrier as well as the blood–retinal barrier and prevents inflammations of these organs [12]. Astaxanthin may prevent photooxidative processes caused by UV radiation [17]. It improves the condition of men’s and women’s skin when administered orally. It reduces the depth of wrinkles, reduces age spot size and improves elasticity, skin texture, moisture content in the corneocyte layer and the corneocyte condition [35]. It is a bioactive component of cosmetics (creams, balms, oils, anti-aging serums), providing protection from solar radiation. Natural astaxanthin producers recommend a daily dose of 4–12 mg for health benefits, which is similar to other carotenoids. The immunomodulatory effect was achieved in clinical trials when the daily dose of astaxanthin was 2 mg [33]. The EFSA Panel on Dietetic Products, Nutrition and Allergies recommends that the maximum daily dose of astaxanthin from alga Haematococcus pluvialis (AstaREAL supplements) should not exceed 4 mg (0.06 mg/kg bw per day for a 70-kg person) [36]. Research has not shown that it is possible to overdose on astaxanthin. For example, Buesen et al. [37] did not observe any negative effects of the pigment when it was applied to rats at doses of 700–920 mg/kg/bw. Contrary to other antioxidants, astaxanthin never becomes a pro-oxidant [38].

Depending on the configuration of hydroxyl groups at the asymmetric carbons C3, different configurational isomers of astaxanthin can be formed: the (3R, 3′R) and (3S, 3′S), which are enantiomers, and the meso form (3R, 3′S) (Figure 1). Astaxanthin diastereoisomers differ in their physicochemical and biological properties as well as bioavailability. All of the aforementioned astaxanthin stereoisomers can be commonly found in nature. Their share depends on the source where they are found. The accumulation of astaxanthin isomers in aquatic animals is related to the isomer configuration of dietary astaxanthin (Table 1).

Astaxanthin sources in nature and its configurational isomers.

Astaxanthin Source	Configurational Isomer [%]			References
	3S, 3′S	3R, 3′R	Meso Form
Xanthophyllomyces dendrorhous (yeast)	–	100	–	[42]
Hematococcus pluvialis (algae)	100	–	–	[43]
Petels of Adonis spp.	100	–	–	[44,45]
Crustacyanine (lobster)	33	39	28	[39]
Pandalus borealis (shrimp)	12–25	–	50–53	[39]
Atlantic/Pacific salmon	78–85	12–17	2–6	[39]

The presence of hydroxyl groups in benzoid rings enables esterification of astaxanthin. Esterified astaxanthin is more resistant to temperature fluctuations and photochemical reactions (photolysis, photosensitized oxidation) than free astaxanthin. In nature, astaxanthin can usually be found in the form of mono- and diesters, e.g., in algae and crustaceans’ shells [39]. According to Snoeijs and Häubner [40], in natural zooplankton communities in the Baltic Sea, diesters prevailed during the cold season, but monoesters prevailed in the warm season. Astaxanthin can naturally be found in complexes with proteins or fats. The shells of lobsters, shrimps and other crustaceans contain a bright blue astaxanthin complex with a protein, i.e., crustacyanin. Only after thermal processing (after protein denaturation) is astaxanthin released, and the typical pink color can be seen. The dark green color is astaxanthin lipoglycoprotein, present in lobster ovaries and eggs. Ovorubin is a complex of astaxanthin ester with glycoprotein that gives the red color to the eggs of channeled apple snails (Pomacea canaliculata) [41].

Long thermal processing, even at low temperature, promotes the hydrolysis of esterified astaxanthin and yields free astaxanthin. This fact is very important during the production of smoked salmonoids and dried salted shrimp. Studies showed that the astaxanthin content in cooked shrimp decreased by 78% after four days of direct sun drying due to photodegradation [46]. The content of this pigment was much lower than the content obtained in a jet-spouted bed-drier at 80, 100 and 120 °C [47].

Apart from pigmentation of animal organisms, like other carotenoids, astaxanthin has other metabolic and physiological functions. It has a positive influence on the growth and reproduction of crustaceans [48], sea urchins (Pseudocentrotus depressus) [49], guppies (Poecilia reticulata) [50] and salmonids. A positive effect of astaxanthin supplementation on the reproductive traits of rainbow trout was found. In this case, the astaxanthin content in the eggs and the fertilization rate, the percentage of eyed eggs and hatching were significantly correlated [51]. Studies have shown that astaxanthin supplementation contributes to the health of laying hens by influencing the activity of antioxidant enzymes as well as anti-inflammatory and immunomodulating interleukins. Astaxanthin improves superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px) activities and diminishes malondialdehyde (MDA) content in both the liver and serum. Additionally, astaxanthin alleviates interleukin 2, 4, and 6 (IL-2, IL-4 and IL-6, respectively) in serum [52].

What is Astaxanthin, Its Sources & Benefits – Dr. Berg

FAQ

Is astaxanthin in fish safe?

Nutritional Overshadowing: While astaxanthin offers numerous benefits, it shouldn’t dominate a fish’s diet. Overemphasis can lead to deficiencies in other vital nutrients. Potential Overdose: While astaxanthin is generally considered safe, like any substance, it’s possible for fish to have too much.

Is it safe to eat salmon with color added?

It’s called astaxanthin and it is produced by a photosynthetic microorganism. Farmed salmon typically use this exact pigment as an additive in their food, and it is totally safe (although salmon food has been found to be bad for the environment, that’s another discussion.)

What is the highest source of astaxanthin?

The microalgae Haematococcus pluvialis contains high levels of astaxanthin (about 3.8% of dry weight), and is the primary industrial source of natural astaxanthin.

Is synthetic astaxanthin in farmed salmon?

In farmed salmon, they’re not fed the same diet, so they don’t get the same colour (they’d be grey or off-white). So farms feed them synthetic astaxanthin to give their flesh a red/pink colour. This says that humans that eat the farmed salmon end up consuming the synthetic astaxanthin via the salmon’s flesh.

Do wild salmon eat astaxanthin?

While wild salmon obtain astaxanthin from the algae that they eat, farmed salmon obtain natural or added astaxanthin from their formulated feed. Studies have found that mercury, antibiotics and polychlorinated biphenyls (PCBs) in wild and farmed salmon are relatively low and unlikely to be a health concern.

How much Astaxanthin is in salmon?

“Among the wild salmonids, the maximum astaxanthin content in wild Oncorhynchus species was reported in the range of 26–38 mg/kg flesh in sockeye salmon whereas low astaxanthin content was reported in chum. Astaxanthin content in farmed Atlantic salmon was reported as 6–8 mg/kg flesh.

Are astaxanthin supplements safe?

While moderation is advised, current evidence indicates consuming astaxanthin via salmon is safe. High-dose astaxanthin supplements as tanning pills were linked to retinal toxicity in the 1990s. This raised concerns about eye safety.

Is astaxanthin poisonous?

Yes, the FDA has determined that astaxanthin is “generally recognized as safe” (GRAS), at 0.15 mg/serving. This doesn’t indicate whether there are any health considerations associated with it (that’s not on topic for this site), but it’s not poisonous.

Is astaxanthin legal?

one company has announced it will bring a synthetic astaxanthin supplement to market for human use. Their argument for its legality is that it’s already approved as a color additive in food (salmon). This may be a legal loophole that could potentially bring this far inferior supplement onto health food store shelves sometime in the future.

Does astaxanthin have side effects?

As with many medications and natural products, astaxanthin supplements may have side effects. Astaxanthin is generally safe with no side effects when taken with food. The FDA has placed astaxanthin on the GRAS (generally recognized as safe) list. But astaxanthin is only GRAS at 6 to 7 milligrams (mg) daily.