Microalgae and Its Use in Nutraceuticals and Food Supplements

3.1 Spirulina

Spirulina is a prokaryotic cyanobacterium that has been commercially produced for over 30 years for uses including fish food, vitamin supplements, food dyes, aquaculture, pharmaceuticals, and nutraceuticals [15, 16]. Spirulina is manufactured by many pharmaceutical companies. This alga is thought of as a super food and is widely cultured, primarily in specifically designed raceway ponds and photobioreactors, to meet the current demand.

Spirulina is one of the algae studied for large-scale commercial culture. It grows best at a high pH (9–11) and high bicarbonate concentrations. Generally raceway ponds are used to culture Spirulina. The water depth in the pond is generally 300–500 mm depending on the physical–chemical parameters and density of microalgae. The depth is also dependent on pond size, water flow velocity, and light absorption by the algal culture. Water temperature and pH have a large effect on the productivity of this species. It grows well between the temperatures of 35 and 37°C [17]. Spirulina is a filamentous microalga; hence, its harvesting is relatively easy.

Spirulina contains 60–70% protein by weight (including many amino acids) and contains up to 10 times more beta-carotene than carrots per unit mass [18]. Spirulina is rich in nutrients such as B vitamins, phycocyanin, chlorophyll, vitamin E, omega 6 fatty acids, and many minerals [19]. Spirulina is used for weight loss [20], diabetes [21], high blood pressure, and hypertension [22]. It has documented antiviral [23, 24] and anticancer properties [25]. Spirulina positively affects cholesterol metabolism by increasing HDL levels, which can lead to healthy cardiovascular functions [26]. Romay et al. [27] described the antioxidant and anti-inflammatory properties of C-phycocyanin, which is a prevalent pigment in Spirulina. Essential amino acids like leucine, isoleucine, and valine are significantly present in Spirulina. Spirulina contains fatty acids like linolenic and γ-linolenic acid and ω-3 and ω-6 polyunsaturated fatty acids. Spirulina platensis is a natural source of DHA accounting up to 9.1% of the total fatty acids. The mineral content of Spirulina depends on the water in which it was grown, and its content of iron, calcium, and magnesium provides high nutritional value [16]. Belay et al. [18] reported that Spirulina powder contains provitamin A (2.330 × 10³ IU/kg), β-carotene (140 mg 100/g), vitamin E (100 mg 100/g), thiamin B1 (3.5 mg 100/g), riboflavin B2 (4.0 mg 100/g), niacin B3 (14.0 mg 100/g), vitamin B6 (0.8 mg 100/g), inositol (64 mg 100/g), vitamin B12 (0.32 mg 100/g), biotin (0.005 mg 100/g), folic acid (0.01 mg 100/g), pantothenic acid (0.1 mg 100/g), and vitamin K (2.2 mg 100/g). The amino acid composition of Spirulina is given in Table 2.

3.2 Chlorella

Chlorella is a single-cell, spherical shaped (2–10 μm in diameter), and photoautotrophic green microalga with no flagella. It multiplies rapidly requiring only CO₂, water, sunlight, and a small amount of minerals. Chlorella has been grown commercially cultured in photobioreactors [28] and harvested by centrifugation or autoflocculation. After harvesting the biomass is spray-dried, and the cell powder is sold directly. Chlorella contains 11–58% protein, 12–28% carbohydrate, and 2–46% lipids of its dry weight [29]. It also contains various vitamins such as β-carotene (180 mg 100/g), provitamin A (55,500 IU/kg), thiamin B1 (1.5 mg 100/g), vitamin E (<1 mg 100/g), riboflavin B2 (4.8 mg 100/g), niacin B3 (23.8 mg 100/g), vitamin B6 (1.7 mg 100/g), inositol (165.0 mg 100/g), vitamin B12 (125.9 mg 100/g), biotin (191.6 mg 100/g), folic acid (26.9 mg 100/g), and pantothenic acid (1.3 mg 100/g) [18, 30]. The amino acid composition of Chlorella is shown in Table 2.

Chlorella is able to decrease blood pressure, lower cholesterol levels, and enhance the immune system [16]. It also has the potential to relieve fibromyalgia, hypertension, or ulcerative colitis [31, 32]. The presence of aortic atheromatous lesions was significantly inhibited, and low-density lipoprotein (LDL) cholesterol levels were greatly suppressed upon consumption of Chlorella [33]. Some Chlorella consumers have mentioned a potential correlation between some brands of Chlorella tablets and nausea, vomiting, and other gastrointestinal issues. Chlorella has been labeled as a weak allergen and may be of clinical significance to certain types of people [34].

3.3 Dunaliella

Dunaliella (D. salina) is a unicellular green alga which contains large amounts of β-carotene, glycerol, and protein that can easily be extracted through its thin cell wall. Dunaliella does not required waters appropriate for agricultural and domestic uses and can be cultured in brackish water, marine water, and highly saline water. Global production of Dunaliella is estimated to be 1200 tons dry weight per year [16]. The dominant companies that produce Dunaliella, mainly for beta-carotene production, are located in Israel, China, the USA, and Australia and include Betatene, Western Biotechnology, AquaCarotene Ltd., Cyanotech Corp., and Nature Beta Technologies [35].

Dunaliella produces many carotenoid pigments with the dominant being beta-carotene and smaller amounts of lutein and lycopene [36]. Some strains of Dunaliella contain up to 14% of beta-carotene on dry weight basis. The total carotenoid content of Dunaliella varies with the physicochemical parameters and growth conditions. In optimal environmental condition, it can yield around 400 mg beta-carotene/m² of cultivation area [37]. Carotenoids from Dunaliella are potent free radical scavengers that reduce levels of lipid peroxidation and enzyme inactivation, thereby restoring enzyme activity. Research has shown beta-carotene to prevent cancer of various organs like the lungs, cervix, pancreas, colon, rectum, breast, prostate, and ovary by means of antioxidant activity [36]. It has also been shown to promote regression of certain types of cancer. Supplements of Dunaliella have also shown excellent hepatoprotective effects and reduced the occurrence of liver lesions [38].

3.4 Haematococcus pluvialis

Haematococcus pluvialis (H. pluvialis) is unicellular biflagellate freshwater green microalga. This species is known for its ability to accumulate large quantities of strong antioxidant astaxanthin (up to 2–3% on dry weight) under any conditions. The principal commercial astaxanthin-producing microalga is H. pluvialis [9, 26]. Astaxanthin is used as a nutritional supplement and anti-inflammatory and anticancer agent for cardiovascular diseases and is recently recorded to prevent diabetes and neurodegenerative disorders and stimulates immunization. It also has anti-inflammatory properties and is used for various commercial applications in the dosage forms as biomass, capsules, creams, granulated powders, oils, soft gels, syrups, and tablets [39].

Photoautotrophic culture of H. pluvialis is mainly carried out in open raceway ponds or closed photobioreactors. The accumulation of astaxanthin is affected by environmental factors such as light, temperature, pH, salt concentration, and nutritional stresses. The cellular composition of H. pluvialis varies notably between its “green” and “red” stages of cultivation [40]. Specific biochemical characters of green and red stage of H. pluvialis are described in Table 3. The table shows that carbohydrate content in the green stage is approximately half of the red stage. H. pluvialis can accumulate approximately 5% DW of astaxanthin which is considered as a natural source of this high-value carotenoid protein [37].

3.5 Aphanizomenon

Aphanizomenon is a prokaryotic cyanobacterium commonly found in freshwater systems. There are approximately 500 tons of dried Aphanizomenon produced annually for use in food and pharmaceutical industries [41]. The dominant production source of Aphanizomenon in North America is Upper Klamath Lake and Klamath Falls, Oregon, and currently constitutes a significant part of the health food supplement industry throughout North America. Aphanizomenon contains a significant amount of C-phycocyanin, a light-harvesting pigment. It has antioxidant and anti-inflammatory properties [42]. Aphanizomenon also exhibits high hypo-cholesterolemic activity, significantly greater than soybean oil, which decreases blood cholesterol and triglyceride levels [43, 44, 45]. It also produces polyunsaturated fatty acids (i.e., omega 3 and omega 6), a deficiency of which has been linked to immunosuppression, arthritis, cardiovascular diseases, mental health issues, and dermatological problems [16]. A summary on biochemical characters of all these economically important species is described in Table 4.