Astaxanthin: Sources, Extraction, Stability, Biological Activities and Its Commercial Applications—A Review

There is currently much interest in biological active compounds derived from natural resources, especially compounds that can efficiently act on molecular targets, which are involved in various diseases. Astaxanthin (3,3′-dihydroxy-β, β′-carotene-4,4′-dione) is a xanthophyll carotenoid, contained in Haematococcus pluvialis, Chlorella zofingiensis, Chlorococcum, and Phaffia rhodozyma. It accumulates up to 3.8% on the dry weight basis in H. pluvialis. Our recent published data on astaxanthin extraction, analysis, stability studies, and its biological activities results were added to this review paper. Based on our results and current literature, astaxanthin showed potential biological activity in in vitro and in vivo models. These studies emphasize the influence of astaxanthin and its beneficial effects on the metabolism in animals and humans. Bioavailability of astaxanthin in animals was enhanced after feeding Haematococcus biomass as a source of astaxanthin. Astaxanthin, used as a nutritional supplement, antioxidant and anticancer agent, prevents diabetes, cardiovascular diseases, and neurodegenerative disorders, and also stimulates immunization. Astaxanthin products are used for commercial applications in the dosage forms as tablets, capsules, syrups, oils, soft gels, creams, biomass and granulated powders. Astaxanthin patent applications are available in food, feed and nutraceutical applications. The current review provides up-to-date information on astaxanthin sources, extraction, analysis, stability, biological activities, health benefits and special attention paid to its commercial applications.

The current review provides up-to-date information on astaxanthin sources, extraction, analysis, stability, biological activities, health benefits and special attention paid to its commercial applications.

Introduction
Astaxanthin is a xanthophyll carotenoid which is found in various microorganisms and marine animals [1]. It is a red fat-soluble pigment which does not have pro-Vitamin A activity in the human body, although some of the studies reported that astaxanthin has more potent biological activity than other carotenoids. The United States Food and Drug Administration (USFDA) has approved the use of astaxanthin as food colorant in animal and fish feed [2]. The European Commission considers natural astaxanthin as a food dye [3]. Haematococcus pluvialis is a green microalga, which accumulates high astaxanthin content under stress conditions such as high salinity, nitrogen deficiency, high temperature and light [4][5][6]. Astaxanthin produced from H. pluvialis is a main source for human consumption [7]. It is used as a source of pigment in the feed for salmon, trout and shrimp [1,3]. For dietary supplement in humans and animals, astaxanthin is obtained from seafood or extracted from H. pluvialis [8]. The consumption of astaxanthin can prevent or reduce risk of various disorders in humans and animals [7,8]. The effects of astaxanthin on human health nutrition have been published by various authors [7][8][9][10][11][12][13]. In our previous reviews, we included recent findings on the potential effects of astaxanthin and its esters on biological activities [14][15][16][17][18]. The use of astaxanthin as a nutritional supplement has been rapidly growing in foods, feeds, nutraceuticals and pharmaceuticals. This present review paper provides information on astaxanthin sources, extraction methods, storage stability, biological activities, and health benefits for the prevention of various diseases and use in commercial applications.

Source of Astaxanthin
The natural sources of astaxanthin are algae, yeast, salmon, trout, krill, shrimp and crayfish. Astaxanthin from various microorganism sources are presented in Table 1. The commercial astaxanthin is mainly from Phaffia yeast, Haematococcus and through chemical synthesis. Haematococcus pluvialis is one of the best sources of natural astaxanthin [17][18][19][20]. Astaxanthin content in wild and farmed salmonids are shown in Figure 1. 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 [20]. Astaxanthin content in farmed Atlantic salmon was reported as 6-8 mg/kg flesh. Astaxanthin is available in the European (6 mg/kg flesh) and Japanese market (25 mg/kg flesh) from large trout. Shrimp, crab and salmon can serve as dietary sources of astaxanthin [20]. Wild caught salmon is a good source of astaxanthin. In order to get 3.6 mg of astaxanthin one can eat 165 grams of salmon per day. Astaxanthin supplement at 3.6 mg per day can be beneficial to health as reported by Iwamoto et al. [21].

Structure of Astaxanthin
Astaxanthin is a member of the xanthophylls, because it contains not only carbon and hydrogen but also oxygen atoms ( Figure 2). Astaxanthin consists of two terminal rings joined by a polyene chain. This molecule has two asymmetric carbons located at the 3, 3′ positions of the β-ionone ring with hydroxyl group (-OH) on either end of the molecule. In case one, hydroxyl group reacts with a fatty acid then it forms mono-ester, whereas when both hydroxyl groups are reacted with fatty acids the result is termed a di-ester. Astaxanthin exists in stereoisomers, geometric isomers, free and esterified forms [1]. All of these forms are found in natural sources. The stereoisomers (3S, 3′S) and (3R 3′R) are the most abundant in nature. Haematococcus biosynthesizes the (3S, 3′S)-isomer whereas yeast Xanthophyllomyces dendrorhous produces (3R, 3′R)-isomer [10]. Synthetic astaxanthin comprises isomers of (3S, 3′S) (3R, 3′S) and (3R, 3′R). The primary stereoisomer of astaxanthin found in the Antarctic krill Euphausia superba is 3R, 3′R which contains mainly esterified form, whereas in wild Atlantic salmon it is 3S, 3′S which occurs as the free form [37]. The relative percentage of astaxanthin and its esters in krill, copepod, shrimp and shell is shown in Figure 3. Astaxanthin has the molecular formula C 40 H 52 O 4 . Its molar mass is 596.84 g/mol.   [19,20].

Extraction and Analysis of Astaxanthin
Astaxanthin is a lipophilic compound and can be dissolved in solvents and oils. Solvents, acids, edible oils, microwave assisted and enzymatic methods are used for astaxanthin extraction. Astaxanthin is accumulated in encysted cells of Haematococcus. Astaxanthin in Haematococcus was extracted with different acid treatments, hydrochloric acid giving up to 80% recovery of the pigment [38]. When encysted cells were treated with 40% acetone at 80 °C for 2 min followed by kitalase, cellulose, abalone and acetone powder, 70% recovery of astaxanthin was obtained [39]. High astaxanthin yield was observed with treatment of hydrochloric acid at various temperatures for 15 and 30 min using sonication [40]. In another study, vegetable oils (soyabean, corn, olive and grape seed) were used to extract astaxanthin from Haematococcus. The culture was mixed with oils, and the astaxanthin inside the cell was extracted into the oils, with the highest recovery of 93% with olive oil [41]. Astaxanthin (1.3 mg/g) was extracted from Phaffia rhodozyma under acid conditions [42]. Microwave assisted extraction at 75 °C for 5 min resulted in 75% of astaxanthin; however, astaxanthin content was high in acetone extract [43,44]. Astaxanthin yield from Haematococcus was 80%-90% using supercritical fluid extraction with ethanol and sunflower oil as co-solvent [45][46][47]. Astaxanthin was extracted repeatedly with solvents, pooled and evaporated by rotary evaporator, then re-dissolved in solvent and absorbance of extract was measured at 476-480 nm to estimate the astaxanthin content [17]. Further the extract can be analyzed for quantification of astaxanthin using high pressure liquid chromatography and identified by mass spectra [18].

Storage and Stability of Astaxanthin
Astaxanthin stability was assessed in various carriers and storage conditions. Astaxanthin derived from Haematococcus and its stability in various edible oils was determined [48]. Astaxanthin was stable at 70-90 °C in ricebran, gingelly and palm oils with 84%-90% of retention of astaxanthin content which can be used in food, pharmaceutical and nutraceutical applications, whereas astaxanthin content was reduced at 120 and 150 °C [48]. Astaxanthin nanodispersions' stability was evaluated in skimmed milk, orange juice and deionized water was used as a control [49]. It was found that degradation of astaxanthin was significantly higher in skimmed milk than orange juice. In another study, stability of astaxanthin biomass was examined after drying and storage at various conditions for nine weeks [50]. The results showed that degradation of astaxanthin was as low as 10% in biomass dried at 180/110 °C and stored at −21 °C under nitrogen after nine weeks of storage. The stability of astaxanthin from Phaffia rhodozyma was studied and it was found that stability was high at pH 4.0 and at a lower temperature [51]. The storage stability of astaxanthin was enhanced at 4 °C and 25 °C in a complex mixture of hydroxyproply-β-cyclodextrin and water [52]. Astaxanthin stability was investigated using microencapsulation with chitosan, polymeric nanospheres, emulsions and β-cyclodextrin as reported by various authors [53][54][55][56].

Biochemistry of Astaxanthin
Astaxanthin contains conjugated double bonds, hydroxyl and keto groups. It has both lipophilic and hydrophilic properties [1]. The red color is due to the conjugated double bonds at the center of the compound. This type of conjugated double bond acts as a strong antioxidant by donating the electrons and reacting with free radicals to convert them to be more stable product and terminate free radical chain reaction in a wide variety of living organisms [8]. Astaxanthin showed better biological activity than other antioxidants [11], because it could link with cell membrane from inside to outside ( Figure 4).

Bioavailability
Dietary oils may enhance the absorption of astaxanthin. Astaxanthin with combination of fish oil promoted hypolipidemic/hypocholesterolemic effects in plasma and its increased phagocytic activity of activated neutrophils when compared with astaxanthin and fish oil alone [57]. Astaxanthin was superior to fish oil in particular by improving immune response and lowering the risk of vascular and infectious diseases. The proliferation activity of T-and B-lymphocytes was diminished followed by lower levels of O 2 , H 2 O 2 and NO production, increased antioxidant enzymes superoxide dismutase, catalase and glutathione peroxidase (GPx), and calcium release in cytosol after administration of astaxanthin with fish oil [58]. Bioavailability and antioxidant properties of astaxanthin were enhanced in rat plasma and liver tissues after administration of Haematococcus biomass dispersed in olive oil [14,15,17].
Astaxanthin is a fat soluble compound, with increased absorption when consumed with dietary oils. Astaxanthin was shown to significantly influence immune function in several in vitro and in vivo assays [14,15,17]. Lipophilic compounds such as astaxanthin are usually transformed metabolically before they are excreted, and metabolites of astaxanthin have been detected in various rat tissues [59]. Astaxanthin bioavailability in human plasma was confirmed with single dosage of 100 mg [60]. Its accumulation in humans was found after administration of Haematococcus biomass as source of astaxanthin [61]. Astaxanthin bioavailability in humans was enhanced by lipid based formulations; high amounts of carotenes solubilized into the oil phase of the food matrix can lead to greater bioavailability [62]. A recent study reported that astaxanthin accumulation in rat plasma and liver was observed after feeding of Haematococcus biomass as source of astaxanthin [14,15,17].

Pharmacokinetics
Carotenoids are absorbed into the body like lipids and transported via the lymphatic system into the liver. The absorption of carotenoids is dependent on the accompanying dietary components. A high cholesterol diet may increase carotenoid absorption while a low fat diet reduces its absorption. Astaxanthin mixes with bile acid after ingestion and make micelles in the intestinum tenue. The micelles with astaxanthin are partially absorbed by intestinal mucosal cells. Intestinal mucosal cells incorporate astaxanthin into chylomicra. Chylomicra with astaxanthin are digested by lipoprotein lipase after releasing into the lymph within the systemic circulation, and chylomicron remnants are rapidly removed by the liver and other tissues. Astaxanthin is assimilated with lipoproteins and transported into the tissues [62]. Of several naturally occurring carotenoids, astaxanthin is considered one of the best carotenoids being able to protect cells, lipids and membrane lipoproteins against oxidative damage.

Antioxidant Effects
An antioxidant is a molecule which can inhibit oxidation. Oxidative damage is initiated by free radicals and reactive oxygen species (ROS). These molecules have very high reactivity and are produced by normal aerobic metabolism in organisms. Excess oxidative molecules may react with proteins, lipids and DNA through chain reaction, to cause protein and lipid oxidation and DNA damage which are associated with various disorders. This type of oxidative molecules can be inhibited by endogenous and exogenous antioxidants such as carotenoids. Carotenoids contain polyene chain, long conjugated double bonds, which carry out antioxidant activities by quenching singlet oxygen and scavenging radicals to terminate chain reactions. The biological benefits of carotenoids may be due to their antioxidant properties attributed to their physical and chemical interactions with cell membranes. Astaxanthin had higher antioxidant activity when compared to various carotenoids such as lutein, lycopene, α-carotene and β-carotene reported by Naguib et al. [63]. The antioxidant enzymes catalase, superoxide dismutase, peroxidase and thiobarbituric acid reactive substances (TBARS) were high in rat plasma and liver after feeding Haematococcus biomass as source of astaxanthin [17]. Astaxanthin in H. pluvialis offered the best protection from free radicals in rats followed by β-carotene and lutein [15,17]. Astaxanthin contains a unique molecular structure in the presence of hydroxyl and keto moieties on each ionone ring, which are responsible for the high antioxidant properties [10,64]. Antioxidant activity of astaxanthin was 10 times more than zeaxanthin, lutein, canthaxanthin, β-carotene and 100 times higher than α-tocopherol [65]. The oxo functional group in carotenoids has higher antioxidant activity without pro-oxidative contribution [66]. The polyene chain in astaxanthin traps radicals in the cell membrane, while the terminal ring of astaxanthin could scavenge radicals at the outer and inner parts of cell membrane (Figure 4). Antioxidant enzyme activities were evaluated in the serum after astaxanthin was supplemented in the diet of rabbits, showing enhanced activity of superoxide dismutase and thioredoxin reductase whereas paraoxonase was inhibited in the oxidative-induced rabbits [67]. Antioxidant enzyme levels were increased when astaxanthin fed to ethanol-induced gastric ulcer rats [68].

Anti-Lipid Peroxidation Activity
Astaxanthin has a unique molecular structure which enables it to stay both in and outside the cell membrane. It gives better protection than β-carotene and Vitamin C which can be positioned inside the lipid bilayer. It serves as a safeguard against oxidative damage by various mechanisms, like quenching of singlet oxygen; scavenging of radicals to prevent chain reactions; preservation of membrane structure by inhibiting lipid peroxidation; enhancement of immune system function and regulation of gene expression. Astaxanthin and its esters showed 80% anti-lipid peroxidation activity in ethanol induced gastric ulcer rats and skin cancer rats [14,68]. Astaxanthin inhibited lipid peroxidation in biological samples reported by various authors [14,15,17,18,68,69].

Anti-Inflammation
Astaxanthin is a potent antioxidant to terminate the induction of inflammation in biological systems. Astaxanthin acts against inflammation. Algal cell extracts of Haematococcus and Chlorococcum significantly reduced bacterial load and gastric inflammation in H. pylori-infected mice [16,70,71]. Park et al. [72] reported astaxanthin reduced the DNA oxidative damage biomarker inflammation, thus enhancing immune response in young healthy adult female human subjects. Haines et al. [73] reported lowered bronchoalveolar lavage fluid inflammatory cell numbers, and enhanced cAMP, cGMP levels in lung tissues after feeding astaxanthin with Ginkgo biloba extract and Vitamin C. Another study showed astaxanthin esters and total carotenoids from Haematococcus exerted a dose-dependent gastroprotective effect on acute, gastric lesions in ethanol-induced gastric ulcers in rats. This may be due to inhibition of H 1 , K 1 ATPase, upregulation of mucin content and an increase in antioxidant activities [68]. Astaxanthin showed protective effect on high glucose induced oxidative stress, inflammation and apoptosis in proximal tubular epithelial cells. Astaxanthin is a promising molecule for the treatment of ocular inflammation in eyes as reported by the Japanese researchers [74,75]. Astaxanthin can prevent skin thickening and reduce collagen reduction against UV induced skin damage [14,76,77].

Anti-Diabetic Activity
Generally, oxidative stress levels are very high in diabetes mellitus patients. It is induced by hyperglycemia, due to the dysfunction of pancreatic β-cells and tissue damage in patients. Astaxanthin could reduce the oxidative stress caused by hyperglycemia in pancreatic β-cells and also improve glucose and serum insulin levels [78]. Astaxanthin can protect pancreatic β-cells against glucose toxicity. It was also shown to be a good immunological agent in the recovery of lymphocyte dysfunctions associated with diabetic rats [79]. In another study, ameliorate oxidative stress in streptozotocin-diabetes rats were inhibited by the combination of astaxanthin with α-tocopherol [80]. It is also inhibited glycation and glycated protein induced cytotoxicity in human umbilical vein endothelial cells by preventing lipid/protein oxidation [81]. Improved insulin sensitivity in both spontaneously hypertensive corpulent rats and mice on high fat plus high fructose diets was observed after feeding with astaxanthin [82][83][84]. The urinary albumin level in astaxanthin treated diabetic mice was significantly lower than the control group [78]. Some of the studies demonstrated that astaxanthin prevents diabetic nephropathy by reduction of the oxidative stress and renal cell damage [85][86][87].

Cardiovascular Disease Prevention
Astaxanthin is a potent antioxidant with anti-inflammatory activity and its effect examined in both experimental animals and human subjects. Oxidative stress and inflammation are pathophysiological features of atherosclerotic cardiovascular disease. Astaxanthin is a potential therapeutic agent against atherosclerotic cardiovascular disease [88]. The efficacy of disodium disuccinate astaxanthin (DDA) in protecting mycocardium using mycocardial ischemia reperfusion model in animals was evaluated. Myocardial infarct size was reduced in Sprague Dawley rats, and improved in myocardial salvage in rabbits after four days of pre-treatment with DDA at 25, 50 and 75 mg/kg body weight [89,90]. Astaxanthin was found in rat mycocardial tissues after pretreatment with DDA at dosage of 150 and 500 mg/kg/day for seven days [91]. Astaxanthin effects on blood pressure in spontaneously hypertensive rats (SHR), normotensive Wistar Kyoto rats (NWKR) and stroke prone spontaneously hypertensive rats (SPSHR) were reported [92]. Astaxanthin was found in the plasma, heart, liver, platelets, and increased basal arterial blood flow in mice fed with astaxanthin derivative [93]. Human umbilical vien endothelial cells and platelets treated with the astaxanthin showed increased nitric oxide levels and decrease in peroxynitrite levels [93]. Mice fed 0.08% astaxanthin had higher heart mitochondrial membrane potential and contractility index compared to the control group [94]. Astaxanthin effects on paraoxonase, thioredoxin reductase activities, oxidative stress parameters and lipid profile in hypercholesterolemic rabbits were evaluated. Astaxanthin prevented the activities of those enzymes from hypercholesterolemia induced protein oxidation at the dosages of 100 mg and 500 mg/100 g [67].

Anticancer Activity
The specific antioxidant dose may be helpful for the early detection of various degenerative disorders. Reactive oxygen species such as superoxide, hydrogen peroxide and hydroxyl radical are generated in normal aerobic metabolism. Singlet oxygen is generated by photochemical events whereas peroxyl radicals are produced by lipid peroxidation. These oxidants contribute to aging and degenerative diseases such as cancer and atherosclerosis through oxidation of DNA, proteins and lipids [95]. Antioxidant compounds decrease mutagenesis and carcinogenesis by inhibiting oxidative damage to cells. Cell-cell communication through gap junctions is lacking in human tumors and its restoration tends to decrease tumor cell proliferation. Gap junctional communication occurs due to an increase in the connexin-43 protein via upregulation of the connexin-43 gene. Gap junctional communication was improved in between the cells by natural carotenoids and retinoids [96].
Canthaxanthin and astaxanthin derivatives enhanced gap junctional communication between mouse embryo fibroblasts [97][98][99]. Increased connexin-43 expression in murine fibroblast cells by β-carotene was reported [100,101]. Astaxanthin showed significant antitumor activity when compared to other carotenoids like canthaxanthin and β-carotene [102,103]. It also inhibited the growth of fibrosarcoma, breast, and prostate cancer cells and embryonic fibroblasts [104]. Increased gap junctional intercellular communication in primary human skin fibroblasts cells were observed when treated with astaxanthin [99]. Astaxanthin inhibited cell death, cell proliferation and mammary tumors in chemically induced male/female rats and mice [105][106][107][108][109]. H. pluvialis extract inhibited the growth of human colon cancer cells by arresting cell cycle progression and promoting apoptosis reported by Palozza et al. [104]. Nitroastaxanthin and 15-nitroastaxanthin are the products of astaxanthin with peroxynitrite, 15-nitroastaxanthin anticancer properties were evaluated in a mouse model. Epstein-Barr virus and carcinogenesis in mouse skin papillomas were significantly inhibited by astaxanthin treatment [110].

Immuno-Modulation
Immune system cells are very sensitive to free radical damage. The cell membrane contains poly unsaturated fatty acids (PUFA). Antioxidants in particular astaxanthin offer protection against free radical damage to preserve immune-system defenses. There are reports on astaxanthin and its effect on immunity in animals under laboratory conditions however clinical research is lacking in humans. Astaxanthin showed higher immuno-modulating effects in mouse model when compared to β-carotene [111]. Enhanced antibody production and decreased humoral immune response in older animals after dietary supplementation of astaxanthin was reported [111,112]. Astaxanthin produced immunoglobulins in human cells in a laboratory study [113]. Eight week-supplementation of astaxanthin in humans [72] resulted in increased blood levels of astaxanthin and improved activity of natural killer cells which targeted and destroyed cells infected with viruses. In this study, T and B cells were increased, DNA damage was low, and C-reactive protein (CRP) was significantly lower in the astaxanthin supplemented group [67,102,114]. Recent reports on astaxanthin biological activities are presented in Table 2.

Safety and Dose of Astaxanthin
Astaxanthin is safe, with no side effects when it is consumed with food. It is lipid soluble, accumulates in animal tissues after feeding of astaxanthin to rats and no toxic effects were found [15,17,133]. Excessive astaxanthin consumption leads to yellow to reddish pigmentation of the skin in animals. Astaxanthin is incorporated into fish feed, resulting in the fish skin becoming reddish in color. Antioxidant enzymes such as superoxide dismutase, catalase, and glutathione peroxidase levels significantly increased in rats after oral dosage of astaxanthin [14,15]. A study reported that blood pressure (bp) was reduced in stroke prone rats and in hypertensive rats by feeding 50 mg/kg astaxanthin for five weeks and 14 days, respectively [134]. Astaxanthin was also shown significant protection against naproxen induced gastric, antral ulcer and inhibited lipid peroxidation levels in gastric mucosa [67,135]. Astaxanthin accumulation in eyes was observed when astaxanthin was fed to rats [136]. Astaxanthin extracted from Paracoccus carotinifaciens showed potential antioxidant and also anti-ulcer properties in murine models as reported by Murata et al. [137]. Astaxanthin bioavailability was increased with supplement of lipid based formulations [14,15,17,138]. Supratherapeutic concentrations of astaxanthin had no adverse effects on platelet, coagulation and fibrinolytic function [139]. Research has so far reported no significant side effects of astaxanthin consumption in animals and humans. These results support the safety of astaxanthin for future clinical studies.
It is recommended to administer astaxanthin with omega-3 rich seed oils such as chia, flaxseed, fish, nutella, walnuts and almonds. The combination of astaxanthin (4-8 mg) with foods, soft gels and capsules and cream is available in the market. Recommended dose of astaxanthin is 2-4 mg/day. A study reported that no adverse effects were found with the administration of astaxanthin (6 mg/day) in adult human subjects [140]. Astaxanthin effects on human blood rheology were investigated in adult men subjects with a single-blind method after administration of astaxanthin at 6 mg/day for 10 days [141]. Recent studies on astaxanthin dosage effects on human health benefits were presented in Table 3. Table 3. Health benefits of astaxanthin in human subjects.  Improved superoxide scavenging activity and lowered hydroperoxides in the human aqueous humor [146] LDL, Low-density lipoproteins, VLDL, Very low-density lipoprotein, CRP, C-reactive protein.

Commercial Applications of Astaxanthin
In the present scenario, production of astaxanthin from natural sources has become one of the most successful activities in biotechnology. Astaxanthin has great demand in food, feed, nutraceutical and pharmaceutical applications. This has promoted major efforts to improve astaxanthin production from biological sources instead of synthetic ones. According to the current literature, astaxanthin is used in various commercial applications in the market. Astaxanthin products are available in the form of capsule, soft gel, tablet, powder, biomass, cream, energy drink, oil and extract in the market ( Table 4). Some of the astaxanthin products were made with combination of other carotenoids, multivitamins, herbal extracts and omega-3, 6 fatty acids. Patent applications are available on astaxanthin for preventing bacterial infection, inflammation, vascular failure, cancer, cardiovascular diseases, inhibiting lipid peroxidation, reducing cell damage and body fat, and improving brain function and skin thickness (Table 5). Astaxanthin containing microorganisms or animals find many applications in a wide range of commercial activities, the reason for which astaxanthin enriched microalgae production can provide more attractive benefits.   US20130004582 Composition and method to alleviate joint pain Reduced joint pain and symptoms of osteoarthritis [164] US20130108764 Baked food produced from astaxanthin containing dough Astaxanthin used in baked food [165]

Conclusion
The current research data on astaxanthin is encouraging and have resulted from well controlled trials in in vitro and in vivo models. Astaxanthin showed potential effects on various diseases including cancers, hypertension, diabetes, cardiovascular, gastrointestinal, liver, neurodegenerative, and skin diseases. Its antioxidant properties are used against oxidative damage in diseased cells. Recently, our laboratory isolated and characterized astaxanthin and its esters from Haematococcus and checked their biological activities in in vitro and in vivo models, confirming that astaxanthin and its esters show potential biological activities in animal models. However, there is a lack of research on astaxanthin esters (mono-di) and their metabolic pathways in biological systems. Future research should focus on effects of astaxanthin esters on various biological activities and their uses in nutraceutical and pharmaceutical applications. Astaxanthin mono-diesters may increase biological activities better than the free form which can be easily absorbed into the metabolism. Further research requires to be investigated on their metabolic pathways and also molecular studies in in vitro and in vivo models for their use in commercial purposes.