How to Prepare Natural Astaxanthin Powder？

Astaxanthin is a fat-soluble pigment [1] that is reddish-orange in color. It is widely found in crustaceans such as shrimp and crab, and is also an oxygen-containing derivative of carotenoids [2]. In general, a special structure tends to produce special biological functions. A large number of studies have shown that astaxanthin has many physiological activities, such as effectively scavenging free radicals in the body, anti-aging [3], anti-tumor [4], preventing cardiovascular and cerebrovascular diseases [5], cardiovascular diseases [6], protecting the liver [7], anti-diabetes [8], etc. In addition, astaxanthin is a carotenoid that can penetrate the blood-brain and blood-retina barriers, and has a positive effect on improving the central nervous system and brain function [9].

1 Preparation method of natural astaxanthin powder

1.1 Organic solvent extraction method

A large number of studies have shown that acetone has a better effect on the extraction of astaxanthin, because it contains a carbonyl group that is highly similar to astaxanthin. Compared with organic solvents such as methanol, ethanol, and acetonitrile, acetone has the highest recovery rate for astaxanthin extraction [10]. In addition, Sachindra et al. found that a mixed solvent (isopropanol:hexane volume ratio = 1:1) has a higher extraction rate for astaxanthin than a single organic solvent [11]. However, organic solvents such as acetone have the characteristics of low boiling point, volatility, and moderate toxicity, which may pose food safety risks in food processing.

1.2 Microwave-assisted extraction

Microwave-assisted extraction is a new type of extraction technology developed on the basis of traditional organic solvent extraction. Studies have shown that the extraction of astaxanthin from Haematococcus pluvialis using microwave-assisted extraction is an economical and effective method. Microwaves can be transmitted through the microalgal biomass, increasing the intracellular kinetic energy and causing the liquid particles to vibrate. The subsequent increase in cell temperature and cell wall pressure leads to cell lysis. In addition, the microwave-assisted process can shorten the extraction time by breaking the chemical bonds between the molecules of the extraction solvent and promoting the dissolution of ions through the pores in the cell matrix [12]. The microwave-assisted technique can not only improve the extraction efficiency of astaxanthin, but also increase the extraction rate.

1.3 Ultrasonic-assisted extraction

Ultrasonic-assisted extraction is a modern technique for the efficient recovery of astaxanthin from Haematococcus pluvialis. Ultrasonic waves cause cavitation, which rapidly destroys cell walls and enhances the transfer of the extraction agent in the cell matrix [13]. The power of the ultrasonic waves, the temperature and the concentration of the solution are the key parameters for the extraction of astaxanthin. Zou et al. achieved an astaxanthin yield of 27.58 mg/g from Haematococcus pluvialis biomass using ultrasonically assisted extraction under the following conditions: 200 W ultrasonic power, 48% ethanol/ethyl acetate (liquid-to-solid ratio 20:1), 41.1 °C temperature and 16.0 min extraction time.  1 °C, extraction time 16.0 min. Under these conditions, ultrasonic-assisted extraction was used to achieve an astaxanthin yield of 27.58 mg/g from Haematococcus pluvialis biomass [14]. 

1.4 Enzymatic hydrolysis

Natural astaxanthin exists in three forms: free astaxanthin, astaxanthin monoesters and diesters. The main form is the more stable astaxanthin lipid, i.e., astaxanthin monoesters and diesters [15-16]. The methods for deglycerolizing astaxanthin esters are saponification and enzymatic hydrolysis. In order to evaluate the relative efficiency of enzymatic and saponification on the demethylation of natural astaxanthin esters, Su et al. found that the use of cholesterol esterase can completely hydrolyze astaxanthin esters, and its degradation and isomerization are significantly reduced [17].

1.5 Supercritical fluid extraction

Supercritical fluid extraction involves using supercritical CO2 as an extraction solvent to contact the raw material containing astaxanthin. The optimal conditions for extracting astaxanthin are obtained by adjusting different extraction parameters (temperature, time, pressure, additives, etc.). Supercritical CO2 extraction can be used to maximise the retention of the biological activity of astaxanthin, and the extraction and separation processes can be combined into one.

Supercritical fluids are a special fluid state of matter. They refer to substances that can be extracted from solids like a gas and dissolve substances like a liquid at temperatures and pressures above the critical point. Supercritical fluid extraction is an environmentally friendly extraction method because when CO2 is used as a supercritical fluid, solvent-free extraction can be achieved. At the same time, adding hydrocarbons such as ethanol or methanol and natural oils to the system can increase the affinity of CO2 for different solutes, thereby increasing the extraction rate of astaxanthin [1 8]. Cheng et al. used low-pressure supercritical CO2 extraction in a microfluidic reactor to extract broken blood cells extracted with supercritical fluid extraction and an ethanol co-solvent in 30 s. The extraction process was monitored in real time using an optical channel. Approximately 98% astaxanthin was rapidly extracted within 30 s using supercritical fluid extraction and an ethanol co-solvent [19].

1.6 Oil extraction method

The oil extraction method is commonly used to extract natural astaxanthin. Sunflower seed oil and coconut oil can extract up to 26.3 μg/g and 24.7 μg/g astaxanthin, respectively[20]. 7 μg/g [20]. Temperature has a significant effect on the extraction of astaxanthin from linseed oil. At high temperatures (60–90 °C), the oil extraction method can obtain a high recovery rate of astaxanthin. However, the higher the temperature, the more unstable astaxanthin is and is prone to degradation. Therefore, it is crucial to choose the appropriate extraction temperature. In addition, when linseed oil contains astaxanthin, the strong antioxidant effect of astaxanthin can significantly reduce the oxidation rate of linseed oil [21].

2. Functional studies of natural astaxanthin powder

Astaxanthin has a special molecular structure and exhibits biological activities including antioxidant, anti-aging and inhibition of chemical mutagenesis. Numerous studies have shown that astaxanthin has potential beneficial effects in the prevention and treatment of tumors, diabetes, cardiovascular disease, eye disease, skin disease, exercise fatigue, and immunity enhancement [22-58].

2.1 Lowering blood pressure

According to statistics, hypertension is the single largest contributor to the global burden of disease and global mortality. Astaxanthin can effectively treat vascular remodeling by inhibiting vascular smooth muscle cell proliferation and restoring mitochondrial function. In vitro, astaxanthin can reduce the proliferation and migration of vascular smooth muscle cells, lower the level of reactive oxygen species in cells, and balance the activity of enzymes related to reactive oxygen species, including reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, xanthine oxidase, and superoxide dismutase. Chen et al. found that astaxanthin can lower blood pressure and reduce vascular remodeling in spontaneously hypertensive rats through serological tests [22]. A diet supplemented with astaxanthin has a therapeutic effect on hypertension by lowering blood pressure, improving cardiovascular remodeling and oxidative stress status [23].

2.2 Anti-aging

Ultraviolet aging is an important factor leading to aging. Ultraviolet rays reach human skin and produce reactive oxygen species and matrix metalloproteinases, which destroy collagen and elastin, cause melanin deposition and produce skin wrinkles [24]. Astaxanthin has been reported to prevent skin thickening and a decrease in collagen protein to combat UV-induced skin damage [25-27] and slow down the physiological changes caused by UV aging [28]. It has been reported that the addition of astaxanthin to the diet can improve the barrier damage and lack of elasticity of the facial skin caused by ultraviolet light aging, and has good tolerance [29].

2.3 Anti-fatigue

Anti-fatigue effects include delaying the onset of fatigue and speeding up recovery from fatigue [30]. Due to their special molecular structure, natural astaxanthin is highly effective in scavenging free radicals, reducing peroxide levels and strengthening the body's antioxidant system [31]. Astaxanthin can cross the blood-brain barrier and protect the brain from both acute injury and chronic neurodegeneration [32]. The neuroprotective properties of astaxanthin are due to its antioxidant, anti-apoptotic and anti-inflammatory effects [33-34].

In the case of oxidative stress caused by strenuous exercise, natural astaxanthin has the effect of counteracting the production of free radicals and accelerating their removal, showing excellent antioxidant effects. Analysis of the correlation between antioxidant and anti-fatigue effects has found that an increase in antioxidant capacity can enhance anti-fatigue capacity, and the two complement each other. Dietary supplementation with astaxanthin can improve lipid metabolism, carbohydrate metabolism and amino acid metabolism, and has a significant effect on scavenging free radicals and reducing muscle damage [35].

2.4 Eye protection

Studies have shown that astaxanthin can reduce the content of retinal protein oxides in the retina of rats through its antioxidant effect, inhibit ischemia-induced retinal cell death, and reduce high blood pressure-induced retinal cell apoptosis, playing a key role in repairing retinal damage [36]. Astaxanthin can therefore play a beneficial role in a variety of eye diseases, including delaying the development of metabolic cataracts [37] and improving tear stability in patients with dry eyes and relieving eye fatigue [38].

The neuroprotective effect of astaxanthin can also be used in the treatment of glaucoma. Elevated intraocular pressure can cause deformation of the sieve plate and disrupt blood flow, leading to loss of axons and apoptosis of retinal ganglion cells, accompanied by typical optic nerve damage [39]. In addition, astaxanthin has good safety and no adverse events have been reported in clinical studies [40-41].

2.5 Boosts immunity

The immune system is highly sensitive to damage caused by free radicals. Astaxanthin not only donates electrons to free radicals, but also binds to them to form harmless compounds, thereby scavenging free radicals or terminating the chain reaction of free radicals and restoring the immune system's defense mechanisms.

To investigate the effect of astaxanthin on the immune system, Park et al. used female domestic cats as a model animal. The study showed that astaxanthin-fed cats had increased proliferation of peripheral blood mononuclear cells and natural killer cell activity [42]. Zhu et al. showed that dietary astaxanthin supplementation improved growth performance, enhanced antioxidant and immune responses, and regulated the expression of relative inflammation-related genes [43]. Jeong et al. confirmed the maturation-inducing and functional-modulating activities of astaxanthin on immune cells, suggesting that the antioxidant effect of astaxanthin may enhance immune system function in cancer therapy [44].

2.6 Anti-diabetic activity

Diabetes is closely related to oxidative stress, which may be the result of increased free radicals, reduced antioxidant defences or both. Generally, the level of oxidative stress in diabetic patients is very high. It is caused by hyperglycaemia, pancreatic β-cell dysfunction and tissue damage [45]. Astaxanthin can lower plasma glucose and insulin levels and improve systemic insulin sensitivity and insulin-stimulated glucose uptake.

Astaxanthin treatment significantly improves glucose tolerance and alleviates pancreatic islet beta cell dysfunction, inhibits dyslipidemia and oxidative stress, increases the activity of antioxidant enzymes, and ultimately improves reproductive outcomes [46]. Astaxanthin is also a promising immunomodulatory agent in the recovery of lymphocyte dysfunction in diabetic rats [47]. The addition of astaxanthin can significantly reduce blood glucose and increase insulin levels in mice due to a high-fat, high-fructose diet [48].

2.7 Antitumor

Astaxanthin can inhibit the tumorigenic activity of stress-induced natural killer cells through its own antioxidant properties. Astaxanthin effectively improves stress-induced immune dysfunction and can even regulate the activity of some genes to inhibit the metastasis of malignant tumors [49]. Faraone et al. showed that astaxanthin induces cell cycle arrest in tumor cells, inhibits tumor metastasis, enhances the sensitivity of tumor cells to chemotherapy, and limits its adverse reactions [50]. Although astaxanthin, canthaxanthin and β-carotene all inhibit tumor growth, astaxanthin has the highest antitumor activity [51].

Astaxanthin modulates immune responses, inhibits cancer cell growth, reduces bacterial load and relieves inflammation of the gastric mucosa, and prevents oxidative stress caused by ultraviolet light [52]. Zhang et al. showed that astaxanthin can inhibit the proliferation and growth [53]. Yasui et al. showed that the pro-tumor necrosis factor and anti-inflammatory factors secreted by astaxanthin can effectively inhibit the growth of colon cancer cells and induce apoptosis of cancer cells [54]. In addition, astaxanthin can effectively prevent stomach cancer and bladder cancer [55], as well as effectively remove free radicals produced in the body by light radiation, reduce photochemical damage to the skin, and prevent skin cancer. Inflammation is an effective means of preventing and treating cancer. In this way, inhibiting the expression of inflammatory cytokines leads to the cessation of the cancerous process [56]. Studies have shown that astaxanthin has a significant inhibitory effect on a variety of cancer cells, possibly due to their anti-inflammatory effects [57-58].

3 Outlook

In summary, astaxanthin is a carotenoid that is a natural antioxidant with good free radical scavenging ability. The excellent biological activity of natural astaxanthin makes it have broad application prospects and huge market potential, especially in the fields of medicine, cosmetics, health care products, aquaculture, feed additives, etc., which have great value for utilization. At present, research on the relationship between astaxanthin and human nutrition and health is relatively late, and it is mainly focused on in vitro or preclinical levels. Therefore, it is urgent to conduct in-depth research on the mechanism of astaxanthin's effect on human nutrition and health, develop related functional foods, health-care cosmetics, pet feeds, etc., and expand the scope of application and market of natural astaxanthin.

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